Useful Notes / Stock Dinosaurs (Non-Dinosaurs)

Woolly Mammoth by James Havens

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The following extinct animals, to quote Lore Sjöberg, "are not, technically speaking, dinosaurs, but end up in the dinosaur section of the plush toy aisle nonetheless."

This can get quite confusing, as no matter what your dictionary tells you, scientists have been waffling on the subject of dinosaurs for as long as there has been a name for them, although none of the iconic animals have ever been considered dinosaurs.

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Flying Reptiles

Pterosaurs (usually called pterodactyls in media and in pop language) are often referred as the "flying dinosaurs". They were closely related to them, but were not true dinosaurs.

Pterosaurs in Media

In Real Life, pterosaurs were the dominant large flying creatures in the Age of Dinosaurs. They coexisted with their land-dwelling relatives for 160 million years, and eventually went extinct together with the last nonbird dinosaurs. As with dinosaurs, there are many common mistakes when it comes to pterosaur portrayals in media — and we're not just talking about simple Anachronism Stew and Misplaced Wildlife here.

• In fiction, these reptiles usually act as airborne terrors to menace humans and/or other animals, usually grabbing them with eagle-like feet and being strong enough to lift and carry their victims in flight, often giving them to their nestlings just like eagles. In Real Life, pterosaurs had very weak legs with non-opposable digits and caught their food with their mouths instead. And they didn't have any nestlings to feed: pterosaurs reproduced like sea turtles, burying and abandoning their soft eggs, until the hatchlings (termed "flaplings" by some paleontologists) emerged, strong-boned and ready to fly on their own.
• Especially in older media, they are often portrayed with bat wings, tying into the whole Dinosaurs Are Dragons thing. Actually, their wing membranes were sustained by only one overly-long digit, the fourth one (not the fifth as sometimes shown), which was as robust as the rest of the forelimb. The first, second and third fingers were normal-sized and protruded from the anterior wing-edge like the first digit of modern bats. While most media nowadays have done away with the bat wings, more persistent is the depiction of the wings as loose, bat-like flaps of skin — in Real Life, the wing membranes were thin but taut sheets of muscle, containing several distinct layers of complex muscle fibers that could be slacked and tightened for on-the-fly adjustments.
• We don’t know at all what kind of sounds they emitted in Real Life, but expect to hear them screeching loudly and continuously (usually in a mixed crow-vulture-seagull manner), and also fanning their wings as noisily as possible.
• They tend to be represented as always huge. In Real Life there were many types of pterosaurs (just like modern birds) and they were astonishingly diverse in size, ranging from the size of a crow up to a small airplane.
• They weren't dinosaurs, nor were they birds. Furthermore, they were not even the ancestors of any modern flier^note Dinosaurs were the ancestors of birds; synapsids (below), being the ancestors of all mammals, were the ancestors of modern bats, and invertebrates aren't even worth mentioning in this note: instead, they were only relatives of dinosaurs (and thus birds, of course).

It's worth noting, however, that Science Marches On has been a crucial factor in pterosaur portrayals. Like dinosaurs, pterosaurs have undergone a sort of scientific "renaissance" since the 70s. Before that, they were considered cold-blooded creatures covered in scales and very unlike modern birds. Scientists used to think pterosaurs had weak wing muscles and fragile wing membranes; this would've meant pterosaurs were only awkward gliders — contrasting with the popular view of them as powerful fliers. Since their "renaissance", paleontologists now believe pterosaurs were the first ever vertebrates to be able to fly properly, and nowadays it's clear they were active and efficient fliers with large brains, good eyesight, an excellent sense of balance, skin covered in down-like structures (just like the most bird-like theropods), and high metabolic rates. Due to the structure of their wings, pterosaurs would have been particularly adept at soaring (a bit like modern albatrosses), but they were also able to flap their wings.

Most pterosaurs discovered thus far appear to have lived in marine, coastal, or other watery habitats, but more dry land-loving kinds surely existed as well: some of the smallest species were probably able to climb trees. They were mainly predators of small prey (insects, fish, small land vertebrates etc. according to the species), but some may have been fruit-eaters. Some (especially Pterodaustro) were flamingo-like filter feeders. Like dinosaurs, we don't know what coloration they had, though different kinds of pterosaurs surely had different colors. Modern artists often depict them with motifs reminiscent of those of modern birds, but may also portray them with duller colors (as happens with dinosaurs). Pterosaur locomotion on land has long been a mystery; their footprints were only first discovered in the 1990s. Scientists now think most or all pterosaurs were quadrupedal. Despite all these discoveries and theories, even today the pterosaurs remain one of the most enigmatic groups of prehistoric beasts, as their fossil record has always been one of the scarcest.

Stock Pterosaurs

Very few pterosaurs have been portrayed in non-documentary media, despite their notable variety in Real Life. Among pterosaurs listed here, only four can be called pterodactyls (or more correctly, pterodactyloids) without being totally wrong: Pteranodon, Quetzalcoatlus, Hatzegopteryx, and of course Pterodactylus. The other three, Rhamphorhynchus, Dimorphodon, and Sordes, were more primitive than the former and are usually called rhamphorhynchoids.

Surprisingly, stock pterosaurs are not (necessarily) the biggest/coolest-looking ones — four out of seven are no bigger than an eagle or a stork. Instead, four of them were among the very first scientifically-described species, in the 19th century.

Pterodactylus, Rhamphorhynchus, and Dimorphodon (all mid-sized) were discovered in Europe before the 1820s, the decade in which the first dinosaurs were named. The last two were initially classified as Pterodactylus and recognized as distinct only after the 1820s. Initially, scientists were doubtful if pterosaurs were really fliers: since no modern reptile (in the traditional sense) can fly, some thought they were swimmers using their membranes as flippers, while others believed they were terrestrial. And some, surprisingly, already postulated they were furry like mammals (even though most classical depictions show them scaly). The notion that they were covered with filamentous structures has re-emerged only in The '70s, thanks to new fossil finds of that period, such as Sordes.

With its 7m/24ft wingspan, Pteranodon was found in the USA in the last quarter of the 19th century, during the "Bone Wars."^note Oddly, it too was initially classified as Pterodactylus. Its sheer size ("Whoa the biggest flier ever!") and its crest soon made it the new iconic pterosaur, and it still holds that status today.

Several interesting new pterosaurs were discovered in the second half of the 20th century: among them, Dsungaripterus, Pterodaustro, Tropeognathus, Anhanguera, Tapejara, Eudimorphodon, and the aforementioned "hairy" Sordes; but only one managed to achieve some consideration in the media: Quetzalcoatlus, because it was the only one clearly bigger than Pteranodon, and the new "biggest flying animal ever." In the 2000s, Tropeognathus gained some popularity as well thanks to a memorable appearance in Walking with Dinosaurs (as "Ornithocheirus"), but only because it was (wrongly) described as the biggest flying animal that ever existed, but not enough to be listed here. In the 2010s, Hatzegopteryx, found in year 2003 in Romania, also gained some fame thanks to its size, being possibly bigger than Quetzalcoatlus itself.

Giant Flier, but not Toothy: Pteranodon ***

Pteranodon lived 86-84 million years ago on the shorelines of the inland sea that covers what is today Kansas, Nebraska, and other midwestern U.S. states. It had the typical traits of the most evolved pterosaurs, the pterodactyloids (aka literal pterodactyls). It had an elongated head, weak hindlimbs, only a hint of a tail, and very long wings with a huge "wing-finger," while the other digits were very small and may have been almost useless. It was one of the most specialized flying animals that ever lived, but very clumsy on land, where it walked slowly on all fours. With a wingspan of 6m/20ft, it was once considered the largest animal to ever fly, and the absolute limit for flying animal size.

It was thought pteranodonts lived a bit like modern seashore birds, laying their eggs on cliffs and using ascendant winds to take off. However, the takeoff method is now known to have been wrong; rather, pteranodonts, like all pterosaurs, could vault from the ground with their wings, like bats do. Roosting on cliffs is not entirely unlikely, though. Like the modern albatross, they may have been vagrant or migratory. Contrary to what is sometimes said, Pteranodon probably didn’t survive enough to see the meteorite — its fossil record ends a dozen million years before the mass extinction. Until 2018, only azhdarchids were known from fossils as late as 66 mya; one of them was Quetzalcoatlus (see below). Findings early in 2018 revealed that pteranodontids and their smaller, more derived relatives, the nyctosaurids, also reached that point, though Pteranodon itself still hasn't left any fossils from that time.

The backwards-pointing crest is the most striking feature of Pteranodon. It was laterally flattened in Real Life, but in media expect to see it with a conical shape, often resembling a horn. The real purpose of this crest is still unclear. It is traditionally described as a sort of balancing pole to better balance the long head, or as a rudder to keep it stabilized during flight. However, this doesn’t explain why only males had such a big crest, while the females’ one was extremely shortened. It was once thought long- and short-crested individuals belonged to different species.^note Astonishingly, short-crested pteranodonts are almost never shown even in documentary media! This bony protrusion may have simply been a display device, as is also hypothesized for Stegosaurus’ plates, Triceratops’ horns and frill, Spinosaurus’ "sail", and so on. This could explain why the males’ one was so big compared with the females.

In popular portrayals, an ever-present mistake is to show Pteranodon as toothed. When present, these teeth usually resemble those of the other well-known pterosaur, Rhamphorhynchus (see below). The fact that the genus’ name ends in -odon (meaning tooth in Greek) may mislead people. Actually, -odon is preceded by the Greek "privative a-" (becoming an- when followed by a vowel). Thus, anodon means toothless (see also Ludodactylus).

In Real Life, Pteranodon was basically a giant pelican in behavior. Its long toothless beak was useful for catching fish, and the shape of its lower jaws seem to show a sort of "pouch" to store fish in flight, though this is not certain. It was once thought that Pteranodon would snatch fish on the fly with its beak, but now it's believed that it would have dived into the water and swam for food (again, much like a brown pelican; the other species of pelicans don't dive). If alive today, Pteranodon wouldn't be the danger for humans that it usually is in media. Weighing only about 50kg/110 lbs and having bones even hollower than those of birds, it was too light to lift a 70kg man off the ground. And even if it could, it wouldn't have used its weak hindlimbs, but its mouth instead. Finally, since its beak was straight and smooth-edged, a child could easily have escaped it by wriggling.

Pteranodon’s nifty crest, along with the fact that it held the size record for almost a century, has made it THE pterosaur in popular imagination. Its iconic status among pterosaurs could be partially justified. It’s not only one of the first-discovered pterosaurs, but perhaps also the most common in the fossil record. Hundreds of specimens are known, while most other pterosaur genera are much, much rarer, often known from a single individual. The vast majority of pteranodonts belong to the species everyone knows, Pteranodon longiceps, the latter word meaning "long head" for its slender, pointy crest. The other species Pteranodon sternbergi had a somewhat more rectangular crest, which has lead some scientists to classify it as its own genus, Geosternbergia.

1. Entry Time: 1925
2. Trope Maker: The Lost World (film)

Smaller Flier, but Toothy: Rhamphorhynchus **

Rhamphorhynchus longicaudus ("long-tailed sharp beak") was first found in Germany in the 19th century, and lived in the Late Jurassic in the same location as several other pterosaurs, as well as Archaeopteryx and Compsognathus. It was the second named pterosaur after the prototypical Pterodactylus (see below), and the first one known with a long tail. It’s the namesake of the primitive pterosaurs called rhamphorhynchoids. Like Archaeopteryx, Rhamphorhynchus has left exquisite remains. Some specimens with prints of wing membranes have been known since the 19th century. It was just these Rhamphorhynchus that definitively showed pterosaurs were airborne critters, not water-dwelling as believed by some at the time.

Rhamphorhynchus had a wingspan of about 2m/6ft, relatively short wings, a narrow snout slightly pointing upwards^note Even though classic portraits show it with a straight snout, robust hindlimbs, and long tail. Two recognizable traits are the protruding teeth and the diamond-shaped "fin" set vertically on the tip of its tail. As Rhamphorhynchus lived in coastal lagoons, the teeth were probably apt to catch fish by swimming and diving, much like Pteranodon did. The typical tailfin was made of soft tissue (it’s known only thanks to prints in the rocks).

Rhamphorhynchus’ tail has often been compared with a dragon’s or a devil’s, and the large teeth give it a deceptively "menacing" look (it wouldn’t be more dangerous than a gull if alive today). We also now know it was covered in hair-like structures, like its relative Sordes pilosus (which just means "hairy devil").

Its striking look, the earliness of its discovery, and the completeness of many remains have contributed to making Rhamphorhynchus the second most commonly portrayed pterosaur in media — especially older media. In particular, the Pellucidar series by Tarzan creator Edgar Rice Burroughs features the Mahars — an evil, intelligent race of psychic Rhamphorhynchus. And Ray Harryhausen's movie One Million Years B.C. shows a huge, short-tailed (and tailfin-lacking) "rhampho" winning an aerial battle against an equally huge (but correctly toothless just for once) Pteranodon. The species has become quite rare today — pterosaurs shown in the most recent movies generally are Pteranodon or (more commonly) a fictional species.

Like Pteranodon, Rhamphorhynchus tends to be portrayed incorrectly in fiction, often as big as a Pteranodon or even bigger. Another classic mistake is to show the "rhampho" with a flexible tail (a bit like what happens to the "raptor" dinosaurs) and often ending with triangular, arrow-like fins, like here. In reality, their tail was stiffened by bony tendons and was a steering device during flight.^note It's been suggested that only males had the "fin", butthis cannot be proven. But if this is true, then this thing could have been for display. Finally, a very Undead Horse subtrope is to apply the "dragonish" rhamphorhynchoid tail to every other pterosaur, especially Pteranodon. Actually, pterodactyloid pterosaurs had stubby tails without distinction. Some specialized rhamphorhynchoids had also short tails, like the tiny Anurognathus.

1. Entry Time: 1910s
2. Trope Maker: E. R. Burroughs' Pellucidar

Huge, Mythical Beast: Quetzalcoatlus **

This has been considered the ultimate Giant Flyer among prehistoric animals. Living in North America at the very end of the Cretaceous, 68-66 mya (but some think its distribution was worldwide), Quetzalcoatlus northropi was discovered in the 1970s in Texas from incomplete remains. Its wingspan was estimated from 10m/35ft up to 16m/50ft, with the lower range being the most likely. Of course, pop-media has often followed the higher one. This "living airplane" took Pteranodon's reputation over as "the biggest flier ever" in those years. Its describer named it from an Aztec divinity, Quetzalcoatl, the "feathered snake" — the animal itself is often called "the quetzalcoatl". Its name also recalls that of the modern Quetzal, the long-tailed bird sacred to the Aztecs. In 2021, a second smaller-sized (6m/20ft wingspan) Quetzalcoatlus species, Quetzalcoatlus lawsoni, was described.

Weighing about 200 kg, Quetzalcoatlus was long described as similar to an upscaled Pteranodon (which weighed less than half that). Indeed, both animals had a long toothless beak and an atrophied tail. Some depictions show Quetzalcoatlus with a small cranial crest, others show it crestless. Compared to Pteranodon, Quetzalcoatlus had much longer, stronger hindlimbs, a bigger body, a longer, stiffer neck, and shorter, wider wings with the "hands" closer to the wingtips than to the shoulders. Its diet has long been an enigma (Fish? Carrion?), but in the 2000s, scientists re-studied its anatomy, and today Quetzalcoatlus is thought to have been a mainly terrestrial animal, walking on its four long limbs, and eating small land critters like a stork. ^note It's worth noting that the terrestrial hypothesis was already postulated just after the first find, but initially not demonstrated.

The astonishing thing is, in spite of being as tall as a giraffe when on land, Quetzalcoatlus could still fly. As absurd as this sounds, pterosaurs had two key traits that allowed them to grow massive without becoming flightless. The first is that for their body size, pterosaurs were even lighter than birds, having totally hollow bones like straws and air sacs in their wing membranes; Quetzalcoatlus itself was about the size of a giraffe yet was only a quarter of the weight. Secondly, the quadrupedal stance of pterosaurs allowed them to take off on all fours, starting with the wings — a much more cost-efficient method of takeoff compared to the two-legged strategy used by birds. Given its size, it should have been an extremely powerful flier, capable of frequenting several habitats, and maybe even traveling worldwide.

Despite its impressiveness, Quetzalcoatlus has only received great attention in dino-books and documentaries, with being rare in films and dino-stories. This is especially unusual given that with its size, diet, and terrestrial habits, it would have been the only of the classic five stock pterosaurs capable of killing and eating humans if alive today. However, Quetzalcoatlus still has some notable pop-culture appearances under its belt, such as being one of the central characters of Dinoverse and being regularly ridden by the characters in Dinotopia, where they are known as "skybaxes" — it even appeared in the Captain Underpants series as the Kid Heroes' Team Pet in the later books! The "quetz" wouldn't make its Hollywood debut however until 2022's Jurassic World Dominion, being one of the most accurate designs in the franchise and possibly its first pop-media depiction as a dangerous creature rather than the Gentle Giant of the abovementioned literary appearances. A downsized Quetzalcoatlus flying robot capable of flapping its wing was built in the 1990s, although it did not have the proportions that the animal is now known to have had (a case of Science Marches On). Another less-complex flying robot built in the same years represented Pteranodon.

1. Entry Time: 1990s
2. Trope Maker: Dinotopia books

The first-named Reptile of the Mesozoic: Pterodactylus **

Rarely will you see any other pterosaur in fiction, but if you do, it will either be Pterodactylus or Dimorphodon. In the original novel The Lost World, the two scientists argue if the pterosaurs they meet are one of the two. Whatever kind they were, they are enormously oversized — even bigger than a Pteranodon. In Real Life both were not bigger than a large seagull. In recent stories, Pterodactylus and Dimorphodon are rarely portrayed, but have traditionally been common in documentary media due to their historical relevance.

Discovered in 1784, Pterodactylus was not only the first pterosaur ever found, but the second Mesozoic reptile known to science (the first being the sea reptile Mosasaurus; see below) and the first fossil animal to be recognized as being like nothing alive today (well before the first dinosaurs) — and this was back when concepts like "extinct" and "antediluvian" (the word "prehistoric" came later) were still highly controversial. Obviously, Pterodactylus was the very first flying reptile ever found, and even early paleontologists tended to refer to the whole group as 'pterodactyls' long before the word "pterosaur" was coined; this explains why 'pterodactyl' has become the stock name of pterosaurs.

Over 50 Pterodactylus species were recognized in the past, but most are now under different genera (some of which actually lived alongside it), including Rhamphorhynchus, Dimorphodon, Pteranodon, Dsungaripterus, Germanodactylus, Aerodactylus^note yes, this one is named after that pterosaur Pokémon, Gnathosaurus, Campylognathoides, Lonchodraco, Ardeadactylus, Dorygnathus, Scaphognathus, and Ctenochasma. Today, only one (the original) has remained valid, Pterodactylus antiquus ("ancient winged finger"), about the same size of a Rhamphorhynchus. Some alleged Pterodactylus species were described from individuals no bigger than a sparrow: this led the genus to be described as "one of the tiniest pterosaurs ever." Recent research suggests these specimens were actually newborns, which deceptively resemble miniaturized adults. The fact that newborn pterosaurs were virtually identical to adults is a very recent discovery (made in the 2000s) that astonished scientists: none of the extant fliers shows powered flight soon after its birth. This tells us that pterosaurs were fully independent at birth, and thus did not care for their young.

Pterodactylus was one of the first pterodactyloid pterosaurs to appear (Late Jurassic Europe), and shared its habitat with the more archaic Rhamphorhynchus. Its body shape was more similar to a miniaturized pteranodont than to a rhamphorhynch, with long, thin jaws, elongated wings, weak hindlimbs, small "wing-hands," and a stubby tail. Usually depicted as a generic-as-it-gets pterosaur, the latest findings show it had a small crest made of skin on the back of its head. Moreover, its apparently generic teeth could have been specialized for something — traditionally described as a fish- or insect-hunter, Pterodactylus could have been a filter feeder in coastal lagoons (though not so specialized as its cousin, Pterodaustro) or perhaps a wader/prober like a shorebird.

1. Entry Time: 1854
2. Trope Maker: Crystal Palace Park

Primitive Bighead: Dimorphodon **

Dimorphodon was a rhamphorhynchoid that lived in Early Jurassic, 195-190 mya — the most ancient of the stock pterosaurs. Found in England, it shared with Rhamphorhynchus the elongated stiffened tail, but we don't know if it had a "fin." Its most striking trait was its oversized skull, even bigger than the body itself! Despite appearances, the head of Dimorphodon was lightened by wide openings in the skull, and the animal couldn’t have had trouble lifting it, a bit like modern toucans and hornbills with their beaks.

Its name, "two-shaped teeth," recalls that of the famous Dimetrodon ("two-measured teeth"). It had two kinds of teeth (while most pterosaurs had only one or none). Some teeth were bigger and sparse among the smaller ones. With this kind of dentition, the feeding habits of Dimorphodon have always been matter of speculation. It could have been a fisher, a hunter of small land animals, or an insectivore. Newer evidence reveals that the latter two were more likely, however, as it has few to no adaptations for fishing, but many for terrestrial hunting and leaf-litter grubbing.

Dimorphodon is often depicted as a frequent flyer (the Dinotopia books even portray it as an Instant Messenger Pigeon!), but later research suggests that it was quite the opposite. While Dimorphodon could fly, it was also rather heavy for such a small animal, making flight rather strenuous for it. It's believed that, like similarly loaded birds, Dimorphodon would have only flown in times of emergency. Interestingly, this is not an illustration of Dimorphodon's primitiveness, as many pterosaurs before it were excellent flyers. This likely means that Dimorphodon's poor flight ability was actually an evolutionary adaptation for chasing bugs, lizards, and small mammals through the undergrowth.

More archaic than Rhamphorhynchus, Dimorphodon shows several primitive traits which betray how dinosaurs and pterosaurs were closely related. The three free wing-fingers were strong and large-clawed, not unlike those of a feathered theropod (indeed, its species name, macronyx, means "large claw"), and the hindlegs were long and powerful. Its stocky skull was more similar to a theropod dinosaur than to a pterosaur, with nasal openings on the tip of the nose (most pterosaurs had nostrils just in front of the eyes). A strange anatomical feature is one elongated digit in each hindfoot, which could have been attached to the wing membrane. If so, the dimorphodont could have used it to better control its flight, like modern bats do with their feet. More evolved pterosaurs lost this super-toe altogether. Despite its primitive anatomy, Dimorphodon was a true pterosaur with all the pterosaurian traits (see also Eudimorphodon).

Dimorphodon was discovered in 1828 by the famed Mary Anning, who also found the first plesiosaurs and icthyosaurs (see below). These same rocks, found along the coast of southwest England in Dorset, also produced Scelidosaurus and are today a World Heritage Site known as the Jurassic Coast. Despite its historical significance, it doesn't typically appear in the media beyond dinosaur books. However, this might be due for a change with the release of Jurassic World, which had Dimorphodon as a featured creature (naturally in the "winged menace" role).

1. Entry Time: 1912
2. Trope Maker: The Lost World

Giant Among Dinosaurs: Hatzegopteryx *

Quetzalcoatlus was not the only gigantic azhdarchid. Since the 90s, others have been discovered with a similar estimated wingspan, e.g. Arambourgiania. But at an estimated 250 kg, Hatzegopteryx thambema was the heaviest of them, and quite possibly the biggest pterosaur (and flying animal in general) of all time, a real "Badassodactylus".

Hatzegopteryx lived on and was named after the Late Cretaceous "Hateg Island", which existed in what is today Transylvania, Romania.

Here, dinosaurs a fraction of the size of their mainland cousins lived: cow-sized sauropods (Magyarosaurus), human-sized hadrosaurs (Telmatosaurus), sheep-sized ankylosaurs (Struthiosaurus), and dog-sized iguanodontians (Zalmoxes), but no big predatory dinosaurs. Hatzegopteryx was a peculiar creature for many reasons; while the island was home to dinosaurs that were subject to island dwarfism, Hatzegopteryx went the opposite direction and was subject to island gigantism, being as tall as a giraffe. This would have put Hatzegopteryx on the top of the island's food chain. Additionally, unlike most other azhdarchids, Hatzegopteryx likely had an extremely thick and muscular build and a relatively short neck. This implies that Hatzegopteryx hunted significantly larger prey than other azhdarchids (potentially up to the size of a cow). It could have swallowed a whole Struthiosaurus, armor and all, or speared a Magyarosaurus with its huge beak. Even though the Hatzegopteryx's wingspan was probably not wider than that of Quetzalcoatlus, its skull was much bulkier, and was probably as massive and long as the skull of a large theropod or ceratopsid dinosaur, and thus one of the biggest skulls among non-marine animals that has ever existed.

Hatzegopteryx is the most recent pterosaur to attain "stock" status, at least as far as nonfiction works are concerned (hence the one star above). First described in 2002, it made its media debut in the 2011 documentary Planet Dinosaur, which was unfortunately made before the species' robust body plan was known. It has since appeared in The Isle, as an unlockable creature in Jurassic World: The Game, and in Prehistoric Planet.

1. Entry Time: 2011
2. Trope Maker Planet Dinosaur (documentary)

Revolutionary Hairs: Sordes *

Among the numerous pterosaurs outside the classic five — Pteranodon, Rhamphorhynchus, Quetzalcoatlus, Pterodactylus, Dimorphodon — we might also mention the very short-named Sordes pilosus. Even though its name is usually translated into "hairy devil", but technically "sordes" is Latin for "filth" or "scum" and is a feminine word under the Latin rules of grammar, meaning its species name should be rewritten as pilosa (Latin feminine of hairy) according to some.

Very similar to Rhamphorhynchus, this small (2 ft of wingspan) Late Jurassic rhamphorhynchoid from Kazakhstan, in the former U.S.S.R., has nonetheless had an enormous relevance in ptero-science; it was the first pterosaur ever discovered with fur-like covering (20 years before the description of the first feathered non-bird dinosaur), and thus led the start to the "Pterosaur Renaissance" briefly described above. Today, many scientists believe all ornithodirans (dinosaurs, pterosaurs, and their common ancestors) were originally covered in filamentous skin structures — feathers and proto-feathers in the case of dinosaurs, "pycnofibres" in the case of pterosaurs. Both dinosaurs and pterosaurs could have inherited this trait from their earliest Triassic ancestors like Lagosuchus and Scleromochlus. The other main archosaurian lineage, the pseudosuchians (crocs and their extinct relatives) never developed these filamentous elements on their skin during their evolution.

In paleoart Sordes can be either shown with or without the classic Rhamphorhynchus fin on its tail, but it is the only one among the pterosaurs found before the Turn of the Millennium that has always been shown "furred" and not naked or scaled like all the others (see also Avimimus for its non-bird-dinosaur equivalent).

1. Entry Time: undetermined
2. Trope Maker: its status as the "first-known furred pterosaur"

Other pterosaurs

Sorry, these ones aren't here. If you're looking for Dsungaripterus, Nyctosaurus, Pterodaustro, Tropeognathus, Cearadactylus, Anhanguera, Tupandactylus, Anurognathus, Eudimorphodon, Harpactognathus, Preondactylus, and others, see here.

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Marine Reptiles

Similarly, these animals are often collectively referred to as "marine dinosaurs," but this time, they were not close relatives of true dinosaurs; most of them were not even related to each other. There were semiaquatic dinosaurs (Spinosaurus, for one), not to mention modern-day diving birds such as penguins, but none of them were completely marine in the way that these reptiles were.

Sea Reptiles in Media

Four main groups of sea reptiles can be recognized in media: plesiosaurs, ichthyosaurs, mosasaurs, and pliosaurs. In Real Life, there were other sea-going reptiles in the Mesozoic, but being less impressive than the above, they don’t gain much attention (except for the giant turtle Archelon, which shows up occasionally). As with most prehistoric animals, only the largest will be mentioned from each group, with the exception of the ichthyosaurs. Ichthyosaurs will be represented only by Ichthyosaurus, which was actually small for the group, though that won't stop writers from making it bigger. However, in old media, Plesiosaurus is frequent as well, even though it, too, was a very small member of its group (although it is regularly shown oversized as well).

Interestingly, unlike dinosaurs, marine reptiles were already well-known to science at the beginning of the 19th century. Their fossil record is overall wealthier and better-preserved than that of the dinosaurs. Significantly, the very first "antediluvian" reptiles to enter into narrative media were not dinosaurs, but the ichthyosaur and the plesiosaur, which battle each other in the novel Journey to the Center of the Earth written by Jules Verne in 1864. Both animals were enormously oversized and depicted in a very fanciful way: more like Mix-and-Match Critter-type sea monsters than their Real Life counterparts. The "ichthyosaur" is similar to a mix-up of whales, crocodiles, dragons and snakes, and doesn't have the familiar fish-like shape of a real Ichthyosaurus. The plesiosaur is a bit more realistic, but has a serpentine neck and the shell of a sea turtle. However, some of these errors are due to Science Marches On, as we’ll see in the individual sections below.

Possibly thanks to Verne, the battle between prehistoric marine reptiles has become stock in paleo-art and pop culture, just like its land-based equivalent of the carnivorous vs. herbivorous dinosaur. One of the opponents is always a long-necked plesiosaur, while the other may alternate between a mosasaur (known plesiosaur predators), an oversized Ichthyosaurus (other ichthyosaurs were plesiosaur predators, but not this one), or a pliosaur (graphic Real Life evidence exists in the form of a decapitated plesiosaur). In these portrayals, ichthyosaurs, mosasaurs, and pliosaurs tend to be used indifferently, often confused each other and portrayed as generic giant swimmers.

Another long-standing cliché makes sea reptiles the pterosaurs' archenemies. You've probably already seen the scene of a prehistoric leviathan emerging abruptly from the surface of the sea, grabbing a giant flying reptile with its jaws (the victim is usually Pteranodon), and dragging it underwater to eat it^note Dougal Dixon once speculated that long-necked plesiosaurs would be specialist seabird/pterosaur hunters if they survived to the present. A good example of this is in Disney's Fantasia, but the cliché itself is much older — an 1830 painting depicts a plesiosaur reaching its neck out of the water to seize a pterosaur. In Real Life, this would be possible only for the biggest mosasaurs and pliosaurs, and even then, we don't have any evidence that either of these preyed on pterosaurs; in fact, we have more evidence that large fish, predatory dinosaurs, and marine crocodiles would have fancied a leathery-winged snack. Giant ichthyosaurs did roam the seas, but in their time, pterosaurs were still very small. Even though giant plesiosaurs like Elasmosaurus could have interacted with giant pterosaurs, their small mouths were unable to swallow Giant Fliers like Pteranodon. Fossils of a juvenile Pteranodon have been discovered in the belly of a plesiosaur fossil, but given what is known about plesiosaur ecology, they were probably scavenged.

Stock Sea Reptiles

Flippered Brontosaurs: Elasmosaurus & Plesiosaurus ***

Plesiosaurs (more correctly, plesiosauroids) are among the most distinctive marine reptiles, and lived worldwide throughout the Mesozoic, 203-66 mya. With their long necks, massive bodies, short tails, small heads, and four paddle-like limbs, their appearance may recall that of a flippered brontosaur, but they were actually very different from sauropod dinosaurs.^note Some plesiosauroids, such as the polycotylids, did not have long necks, instead resembling pliosaurs They were carnivorous, like all known marine reptiles. Their small mouths combined with fossilized stomach contents tell us that they ate only small prey, like fish and squid (although some species might have been specialized to different diets). Their hunting techniques are still a matter of discussion — active hunting, ambush predation, bottom-feeding or even partial filter-feeding are all possible. They had pointed teeth which protruded from their jaws, but whether they had lips is a matter of question; crocodiles don't have lips, as their teeth are lubricated by their watery environment, so it might have been the same with plesiosaurs. For obvious reasons, most go with lipless reconstructions, although the teeth are often oversized and more protruding than in Real Life, resembling the fangs of boa or python snakes.

The association with snakes and turtles seems a constant when describing plesiosaurs. Even scientists used to describe these animals as "a turtle in a snake’s body" or "a snake in a turtle’s body." Their bodies were actually shaped somewhat like sea turtles' (though lacking a shell, of course), and their necks had a huge number of vertebrae (76 in Elasmosaurus!). Classic depictions show plesiosaurs with extremely flexible necks capable of coiling and darting like a snake. Science Marches On however, and it was discovered in the 2000s (thanks to simulations in CGI) that their necks were much more rigid than previously thought, a bit like what has happened to sauropod dinosaurs. Unlike ichthyosaurs (see below) their skin still seemingly preserved small scales, but we don't know how they were colored.

These animals are traditionally described as slow swimmers, using their four flippers as oars and awkwardly propelling their bulk through the water. In classic art, plesiosaurs are usually portrayed in a swan-like posture when surfacing, and often use their necks as periscopes when swimming underwater. According to biomechanical studies, they'd have kept their neck straight to better plough the water, and used their flippers to literally "fly" underwater, alternating movement of the front and back flippers to generate extra lift. Plesiosaurs may have been among the most skilled swimming animals of all time. Like whales compared to dolphins, larger species may have been less agile than smaller ones. There is also evidence of plesiosaurs having a fluke on their tail that acted as a rudder.

The most commonly shown species in recent media is Elasmosaurus platyurus, while Plesiosaurus dolichodeirus is more common in older works. Elasmosaurus was one of the largest plesiosauroids, 40ft/13m long (about as long as a grey whale), but since only a small portion of its length was the body, it weighed "only" 8-10 tons (about as heavy as a large killer whale). The 20ft/7m long neck made more than half the entire length, and was actually longer than the body. Living during the Late Cretaceous in the inland Western Interior Seaway of North America, Elasmosaurus was discovered in the USA shortly before the famous Bone Wars. Its describer, Edward Cope, made an astounding mistake in his first attempt to rebuild its skeleton by putting the head at the end of the tail, and this explains why the animal in the oldest paleo-art has a short neck and an extremely long tail◊. The prototypical Plesiosaurus was the first described plesiosaur (1821), before even the earliest-discovered dinosaurs, Megalosaurus and Iguanodon. First found in Dorset, England by Mary Anning, it was much smaller (16ft long), lived earlier (at beginning of the Jurassic) and was proportionally shorter-necked and longer-headed than Elasmosaurus — though popular portrayals sometimes show it as a miniature elasmosaur, with a longer neck and smaller head than in Real Life.

Possibly thanks to their dinosaurian look and the association with snakes, plesiosaurs have been the most iconic and depicted sea reptiles in media. Like dinosaurs and pterosaurs, expect to see them as scary monsters with a killing attitude. If alive today, even the biggest Elasmosaurus wouldn't be more aggressive than most whales (although they could unintentionally overturn your tiny boat or raft). Needless to say, almost every time a plesiosaur shows up, someone will bring up the Loch Ness Monster (which, if it exists, is extremely unlikely to be a plesiosaur).

1. Entry Time: 1854 (Plesiosaurus); 1933 (Elasmosaurus)
2. Trope Maker: Crystal Palace Park (Plesiosaurus); The Son of Kong (Elasmosaurus)

Flippered Tyrannosaurs: Kronosaurus & Liopleurodon **

The long-necked plesiosauroids belong to the Sauropterygia supergroup, which also includes the Pliosaurs (or pliosauroids, so-called from their traditionally obscure namesake, Pliosaurus; see below) and other lesser-known groups of sea reptiles, like the nothosaurs and placodonts. Together, plesiosauroids and pliosauroids make the group Plesiosauria, a.k.a. "plesiosaurs" in broader sense, originating from the same common ancestor in the Triassic seas. The relationship of sauropterygians to modern reptiles has long been unclear. Once, they were placed with the ichthyosaurs in their own group, and were not believed to be related to any still-living reptilian group. Today, plesiosaurs sensu lato (pliosaurs included) are not thought to be closely related to ichthyosaurs. Instead, they seem distantly related to modern turtles (which actually doesn't help matters that much since turtles themselves are of equally unclear relationship to the other modern reptile lineages).

Pliosauroids first appeared around the same time as plesiosauroids, but did not last as long, going extinct about 95 mya (about 30 mya before the asteroid). Regardless, both subgroups shared the same body plan, with rigid bodies, short tails, and two pairs of powerful flippers — perhaps moved alternately to produce a typical "double-wing" swimming effect (as seen in Walking with Dinosaurs). The difference was in front of their shoulders. Pliosauroids had very short, stocky necks, and their heads were far bigger than that of an Elasmosaurus.^note The earliest pliosauroids still had long necks though, making them strongly resemble plesiosauroids Their teeth were less numerous, but much longer and stronger: like elasmosaurs, expect to see them visible when the mouth is closed. Despite the differences in proportion, the head anatomy of plesiosaurs and pliosaurs was the same. Both had eyes and nostrils placed above to see out of water when the rest of the head was submerged. Both also shared a singular trait: each nostril had two chambers like fish, possibly giving them a directional sense of smell. We don’t know if they passed more time near the surface or in the deeps, but some think pliosaurs were more deep-sea creatures than plesiosaurs.

Pliosaurs were variably-sized, some were no bigger than dolphins, but the biggest ones are candidates for the title of largest sea reptile ever — though their size has often been exaggerated. Among the latter, Liopleurodon ferox and Kronosaurus queenslandicus were some of the top predators of the Late Jurassic and Early Cretaceous oceans respectively. First found in Australia in 1924 and once estimated at 16m/52ft long (10m/33ft is more likely), Kronosaurus is named for Cronus, a Greek Titan who devoured his own offspring (most of the Olympians among them). Liopleurodon was found in Europe in the late 19th century and was very similar to the former, but more primitive, slightly longer-necked, and with less teeth. As is usual with marine superpredators, both are usually depicted as merciless, ever-hungry killing machines. For some reason, unlike dinosaurs and pterosaurs, marine reptiles are usually shown with dull colors, even in modern portrayals. However, some of them might have been very colorful, like modern tropical seagoing animals.

Despite this, pliosaurs have been the least-portrayed group of sea reptiles, and still remain mainly creatures of non-fiction. Kronosaurus was long the most commonly-shown pliosaur in books and documentaries until 1999, when a memorable appearance of an extraordinarily oversized^note The fictional length 80ft/25m was based on misidentified bone fragments; in reality, the species maxed out at 25ft/7m long. Liopleurodon on Walking with Dinosaurs rapidly made it the new iconic member of the family. In the show, an old male Liopleurodon was described weighing 150 tons (a bit less than the blue whale) and the biggest predator of all time. In particular, the scene in which he chomps an ichthyosaur to pieces disturbed many viewers, though the sad final scene where he’s stranded like a whale and slowly dies is shown in a very heartbreaking way. To give an idea about how the animal remained impressed in pop consciousness: all successive depictions have shown Liopleurodons with the WWD mottled blue-and-white color pattern. Another species that is starting to rise in popularity is Pliosaurus funkei, known in popular culture as "Predator X". At an estimated 10m/33ft and 25 tons in weight (originally it was 15m/49ft and 45 tons but Science Marches On), it's likely that it was the largest of this group, and this was coupled with a bite that was estimated to be four times that of T. rex. "Predator X" was featured on 2011's Planet Dinosaur, about a year before it was given its official name by science, making Pliosaurus much more visible in the popular consciousness nearly 200 years after it was first described. And the validity of Kronosaurus falling into question in 2021 (due to the fragmentary nature of the original remains and several specimens being reassigned to new genera, like Monquirasaurus and Eiectus), it is likely Pliosaurus funkei will continue to rise in popularity.

1. Entry Time: undetermined (Kronosaurus); 1999 (Liopleurodon)
2. Trope Maker: Paleo-art (Kronosaurus); Walking with Dinosaurs (Liopleurodon)

Fish, Dolphin, or Lizard? Ichthyosaurus **

Ichthyosaurs have the very evocative name of "fish-lizards": they really resembled large fish in shape and swimming style, but recall modern dolphins as well, thanks to their flippers and their long snouts. Like fishes and unlike dolphins, they had four flippers (their foreflippers were usually bigger) and an upright tail fin.

As a group, ichthyosaurs were the most ancient marine reptiles, and were widespread from the Early Triassic until the Late Cretaceous, 245-90 mya, but went extinct 25 million years before theCtreaceous Extinction for unclear reasons. Once, ichthyosaurs, plesiosaurs and pliosaurs were put together in their own group, the "euryapsids", unified by having a single pair of fenestrae on the top of the skull. Today, "euryapsids" are firmly put in the diapsid group (which also included dinosaurs, pterosaurs and all living reptiles). Ichthyosaurs were among the very first diapsids to have evolved: since they are not related to any modern animal group (thus preventing good comparisons), they still remain quite mysterious critters.

Descended from a still-unknown land-dwelling ancestor (remember, every lineage of marine reptiles descended from four-limbed terrestrial reptiles), ichthyosaurs were the most marine of all marine reptiles and never came onto land, not even to lay eggs. In fact, their young were born alive just like modern dolphins, as we can see in some fossils of mothers dead with their offspring just getting out of their body. We now know that plesiosaurs also reproduced in the same way and probably never left the water either — even though the scene of a long-necked plesiosaur which crawls on the seashore like a sea lion is a staple in artwork. But whereas ichthyoaurs gave birth to multiple tiny young, plesiosaurs only had a single massive baby (up to a third of the mother's size), suggesting the latter took care of their young, like whales do. Ichthyosaurs are extremely abundant in the fossil record: several individuals are preserved with soft tissue and, sometimes, even the imprint of the whole body. Thanks to the latter, we know they had a dorsal fin, a crescent-shaped caudal fin, and four paired "flippers". A strange thing is the backbone curved downwards at the tail level, and filled the lower lobe of the caudal fin, not the upper one — the exact opposite of modern sharks.

Their eyes were notably large for good vision; most portrayals show ichthyosaurs with round pupils and no eyelids, like a typical fish. The skull nasal openings were just in front of the eyes, but the nostrils might have been on top of the head like modern whales (though this is totally speculative). Their skin was smooth and hydrodynamic like a dolphin, as shown in fossil prints: they were perhaps the only reptiles ever whose skin was totally scaleless, convergently with cetaceans. The mouth was usually filled with acute teeth: most ichthyosaurs ate fish, but ammonites and squid were also on their menu. We don't know what percent of time they passed underwater; they may have been able to extract some oxygen directly from the water like modern sea turtles, but they certainly did breathe air like every reptile.

The resemblance to dolphins has classically led artists to show ichthyosaurs jumping out of water in a dolphin-ish style, but this is not proven. Unusually for extinct reptiles, "fish-lizards" often escape the fate of being portrayed as "Sea Monsters"... at least in modern documentaries. Originally, ichthyosaurs were depicted as more crocodile- or mosasaur-like, with no caudal or dorsal fins. The famous ichthyosaur in Journey to the Centre of the Earth is based on this early interpretation. Several other fictional ichthyosaurs have then been inspired by the original.

Today, more updated ichthyosaurs are a regular sight in dino-books. They’re very useful for showing evolutionary mechanisms, providing a classic example of convergent evolution with fish and cetaceans. On the other hand, they're rarely seen in recent stories, much less than the long-necked plesiosaurs. Maybe they're not that exotic-looking, or just not impressive enough to attract writers’ interest. The species shown is always the Early Jurassic Ichthyosaurus communis, because it was the first discovered, back in 1814, before the first known dinosaurs. Like Plesiosaurus and the pterosaur Dimorphodon, it was found in Dorset, England by Mary Anning along what is today known as the Jurassic Coast, the rocks of which date back to the very start of the Jurassic. While it was only 8-10ft long in Real Life, expect to see it oversized (which actually makes it more like its contemporary, the 33ft long apex predator Temnodontosaurus). If shown to proper scale, expect to see its resemblance to dolphins played up heavily; it's likely that its dolphin-like appearance is precisely why Ichthyosaurus maintained "stock" status instead of being displaced by bigger, less dolphinish ichthyosaurs that more closely resemble the leviathan of Jules Verne's story. Some of them, like Cymbospondylus and Shonisaurus, were over 50ft long, and may be the biggest sea reptiles ever, dwarfing even than the much-hyped pliosaurs and mosasaurs.

1. Entry Time: 1854
2. Trope Maker: Crystal Palace Park

Giant Sea-Serpents?: Tylosaurus & Mosasaurus **

The most recent group of Mesozoic sea reptiles, mosasaurs, more properly the Mosasaurids, lived worldwide in the Late Cretaceous, at the end of the Age of Dinosaurs. They replaced ichthyosaurs and pliosaurs in their ecological niches and coexisted with the last plesiosaurs. While ichthyosaurs and plesiosaurs were not closely related to any modern reptile, mosasaurs are the only group of Mesozoic reptiles that literally deserve the title of "giant lizards". They belong to the Squamates (lit. "the scaly ones"), the clade containing modern lizards and snakes^note Never forget, snakes are legless lizards, just as birds are flying dinosaurs, and were closely related to modern snakes and monitor lizards. Indeed, due to their elongated shape, they have often been compared with Sea Serpents, and are often depicted with a speculative dragon-like crest running along their back in old art.

Descended from amphibious monitor-like lizards, mosasaurs often reached gigantic sizes, but exaggerations tend to be common. Some sources speak of 20m long animals, though most giant mosasaurs were probably no more than 14m long. With their slender bodies, they were also less heavy than the robust plesiosaurs and pliosaurs. To be more hydrodynamic, they may have lost the original lizard scales and developed a smooth skin texture (like ichthyosaurs but unlike plesiosaurs), but some skin prints seemingly show they preserved scales on their bodies. Their tails were long and laterally-flattened: like sharks and ichthyosaurs and unlike plesiosaurs, they swam by swinging their tails side-to-side. It's been confirmed that at least some were ovoviviparous (that is, producing eggs that hatch inside the mother’s body). Thus, they would have had no need to come ashore to reproduce, and could live entirely in water. Their fin-like limbs may be further proof. All marine reptiles described here obtained their flipper-like limbs in the same way as modern cetaceans, embedding their original digits in one single fleshy mass, and enormously multiplying the number of phalanges (ichthyosaurs took this to an extreme).

Mosasaur heads were similar to those of modern lizards, but with longer snouts. Like all living lizards and snakes, they'd have had fleshy lips. Like modern snakes, their mouths had notably loose hinges between the jaws; this allowed mosasaurs to swallow large prey without tearing them into pieces (not that they weren't capable of doing so). The teeth were conical or specialized for crushing smaller species and serrated on the three largest species (the 40+-foot giants that are most often depicted), the upper ones placed in two rows on each half-jaw, again like modern snakes and monitors. According to stomach contents, mosasaurs were very generalist feeders: fish, sharks, squids, pterosaurs, early birds like Hesperornis and even smaller mosasaurs have been found.^note This doesn’t necessarily mean they were cannibals, though: the preyed-upon mosasaurs might've been from different species than their predators. After all, modern orcas eat smaller dolphins. We don’t know if mosasaurs had a forked tongue and eyes that didn't close, like many modern squamates, nor if they had heat-sensors like some boas and rattlesnakes; these things usually don't preserve in fossils. Older depictions of mosasaurs usually gave them a rather crocodilian profile, with sword-shaped tails, but reevaluations of the body shape together with the discovery of a shark-like tail fluke on some exquisitely preserved specimens have led to newer reconstructions being more whale-like or ichthyosaurian in appearance, with a more massive upper torso and neck.

Like pliosaurs and ichthyosaurs, mosasaurs are a staple in documentaries, but are not so common in fiction. Most giant leviathans with huge jaws seen in fiction tend to be generic monsters a la Verne, rather than exact species of sea reptiles. Tylosaurus and the clade's namesake Mosasaurus are the stock members of the mosasaur family; needless to say, they're among the largest, up to 10-15m long. The former was first found during the Bone Wars in the USA. The latter has a much more fascinating story. Found in the Netherlands near the Meuse river in 1764 (hence its name), Mosasaurus was the first fossil recognized by science as belonging to a Mesozoic reptile (the second being the pterosaur Pterodactylus). Initially assumed to be a whale or a crocodile, it was eventually recognized as being an extinct lizard unlike any alive today — in fact, it was this animal, along with Pterodactylus, that lead scientists to first propose the concept of "extinction".

In 2015, a (slightly oversized) Mosasaurus received top billing alongside a pack of trained Velociraptors, the already-iconic Tyrannosaurus rex and Chris Pratt in the hit film Jurassic World. The image of her leaping out of the water to be fed a shark was the second major marketing image used for the film (the first being Chris Pratt riding a motorcycle alongside the raptors), and it's been suspected that this film might help contribute to the species becoming more popular among a whole new generation of paleontology geeks. It was also regarded as the most accurate animal in the film despite being slightly oversized, which is quite an achievement in a film that openly acknowledged its own lack of scientific accuracy.

1. Entry Time: 1854 (Mosasaurus); 1940 (Tylosaurus)
2. Trope Maker: Crystal Palace Park (Mosasaurus); Fantasia (Tylosaurus)

The Biggest Sea-Reptiles?: Shonisaurus & Shastasaurus *

Among the rarely-seen marine reptiles in Fictionland, the giant ichthyosaur Shonisaurus deserves special mention because it's been frequently depicted in popular dinosaur books since its relatively recent discover.

In a sense, Shonisaurus ("Shoshone lizard") could be considered the ichthyosaurian equivalent of the giant pterosaur Quetzalcoatlus. Both were discovered in The '70s in the central USA, but their geological epochs were widely different: Quetzalcoatlus lived at the end of the Dinosaur Age, Shonisaurus at the start of it, in the Late Triassic.

Shonisaurus popularis was commonly accepted to have been the biggest ichthyosaur ever, and also the largest animal of the Triassic period — up to 15m/50ft in length and 30 tons in weight, comparable to a humpback whale or a medium-sized sauropod. But in 2004, a new Triassic ichthyosaur entered the fray, Shastasaurus sikanniensis (a species of the traditionally smaller (7m/23ft) ichthyosaur Shastasaurus), a 21m/69ft long leviathan and the new biggest sea-reptile known to science. However, Shastasaurus sikanniensis was originally considered a species of Shonisaurus, and some still argue that it should be considered so; if true, Shonisaurus would detain the record of "Largest Ichthyosaur". However, this could be blown out of the water if and when a more complete specimen of the 2018 "Lilstock ichthyosaur" is found; the current fragmentary remains were estimated via comparison to Shastasaurus to possibly result in a length of 26m/80ft, which if correct puts it within the size range of the blue whale, and thus the second largest animal to ever live.

Shonisaurus and its relatives together comprise the shastasaurians, an early lineage of basal ichthyosaurs that went extinct in the mass extinction at the end of the Triassic, along with numerous non-dinosaur reptiles and mammal ancestors. Shastasaurians had the typical ichthyosaurian fishy or dolphinish shape, but with a more primitive tail rather similar to that of the mosasaurs, longer hind flippers than most ichthyosaurs, few or no teeth in their mouths, and no dorsal fin. Shonisaurus popularis had small teeth only in the front mouth, Shastasaurus sikanniensis totally lacked them. Their lifestyle is uncertain: they may have been to smaller ichthyosaurs as sperm whales are to dolphins and orcas, which is to say slow-swimming hunters of small or medium-sized fish and cephalopods. Some even suspect they could have also been partially filter-feeders, like modern baleen whales.

1. Entry Time: 1980s
2. Trope Maker: Documentary media

Other sea reptiles

Sorry, these aren't here. If you're looking for Stenopterygius, Eurhinosaurus, Opthalmosaurus, Cryptoclidus, Muraenosaurus, Peloneustes, Macroplata, Plotosaurus, Clidastes, Globidens, Opetiosaurus, and others, see here.

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Other Extinct Reptiles

Extinct relatives of modern reptilians are not as common as the above, but some have gained attention in the media. Ancestral extinct reptiles are even rarer sights, but many of them are very interesting and peculiar.

Extant Reptiles in Media

Ancient Colossal Turtle: Archelon **

Archelon ischyros lived in the Late Cretaceous inland shallow sea that once covered the Great Plains of the US. Discovered at the start of the 20th century, it shared its habitat with Elasmosaurus, Tylosaurus, and the flying Pteranodon. Its size and armor made adults virtually immune to most predators.

Not all Mesozoic reptiles were exotic by modern standards; Archelon was simply a sea turtle. But it perfectly fits the subtrope that everything was huge in dinosaur times: it's among the largest known fossil turtles — 4m/13ft long and weighing several tons, Archelon was two to three times bigger than the biggest modern turtle, the leatherback sea turtle). However, it was not the ancestor of modern sea turtles: it belonged to a different lineage, the Protostegids, which went extinct alongside the other giant reptiles at the end of the Cretaceous. Its name is a Portmanteau of arche- (primeval) and -chelon (turtle).

As turtles and tortoises have remained virtually unchanged since their first appearance in the Triassic, Archelon had the same traits seen in modern chelonians: beaked jaws, forelimbs transformed into strong flippers (with multiple phalanges, as usual for sea reptiles), weaker hind flippers and a short tail. However, its armor was lighter than most modern turtles, and the shell may have been leathery instead of horny. The modern turtle which mostly resembles Archelon might just be the aforementioned leatherback. As modern species of sea turtles eat very different items (some eat shellfish, others seaweed, and some jellyfish), we don’t know what Archelon’s preferences were. Almost certainly, it came ashore to lay its eggs like its relatives.

Among Archelon’s appearances in fiction, the most remembered is in Creator/Harryhausen's One Million Years B.C., although upsized to be as big as a house. Surprisingly, many viewers think it was live-acted by a Real Life turtle, but it too is stop-motion like most other animals here. An Archelon named Archie also appears in The Land Before Time film series, in the usual role of the old wise counselor typical for fictional talking turtles. Two fossil Pokémon based on Archelon made their debut in Pokémon Black and White; interestingly, said Pokémon, Tirtouga and its evolved form Carracosta, are actually smaller than their real-world inspiration (4ft tall and 178lbs for Carracosta).

1. Entry Time: 1966
2. Trope Maker: One Million Years B.C.

The Super Crocs of the Mesozoic: Deinosuchus & Sarcosuchus **

Deinosuchus ("terrible crocodile", also called Phobosuchus "fearsome crocodile") was part of the order that contains modern crocodilians. This gigantic alligator (thus more correctly called "Super Gator" than "Super Croc") lived in the Late Cretaceous, but had the same anatomy we see today. Like modern gators, Deinosuchus' skull had wide strong jaws and relatively blunt teeth, contrasting with the narrower jaws and more acute teeth of true crocs and gharials. Its head was as long as a full-grown man, but the length of its body is unknown because little more than the skull has thus far been found. By comparison with modern American alligators, Deinosuchus may have reached 12m in length and weighed up to 8 tons.

Its home was freshwater basins in Late Cretaceous North America, but it could also have frequented the inland sea that divided the continent at the time. Since its fossils date to around 82-73 mya, Deinosuchus probably didn't live long enough to meet T. rex in Real Life, but only the latter's smaller, earlier relatives, like Gorgosaurus and Daspletosaurus. It is usually shown in docu-media ambushing giant dinosaurs like a Nile Croc does with zebras, especially hadrosaurs like Parasaurolophus or Corythosaurus, which is supported by hadrosaur fossils with bite marks from it, but it was likely opportunistic enough to feed on other water creatures, including large fish and turtles (numerous turtle specimens from the time possess Deinosuchus bite marks on their shells). Its reproductive methods are unknown, but it probably built nests on riverbanks for its eggs like modern crocodilians.

Sarcosuchus imperator ("Emperor meat-eating croc") lived earlier than Deinosuchus, in the Early Cretaceous. It was found originally in Brazil and named "Crocodylus" hartii (the genus that includes most modern crocodiles) in 1869, but it was only recognized as a new genus from remains found a century later in Niger, where it lived alongside dinosaurs like Ouranosaurus that could have been its prey. It was a much more primitive animal than modern crocs and not part of the living order of crocodilians, but it resembled today's crocs in shape: with its long thin jaws, it closely recalled the modern gharial of India. It was about the same size of Deinosuchus but slenderer. Its diet is a bit of a mystery — it might have been a generalist, hunting both large fish and dinosaurs (despite appearances, its snout is broader than that of fish-specialist crocodilians, like the previously mentioned gharial).

For obvious reasons, Deinosuchus and Sarcosuchus are popular crocodilian choices in the world of Dinosaur Media, though they're not quite as common in mainstream works as they are in educational ones. Naturally, their size and abilities will usually be exaggerated, though curiously, they tend to avoid Prehistoric Monster territory due to the fact that they were essentially scaled-up alligators/gharials, and we have plenty of them in the modern day to use as points of reference^note Interestingly, sufficiently giant American alligators exist even today — the largest on record was a whopping 15 feet in length and reportedly another one was caught that was around 19 feet — though none of them are as massive as Deinosuchus. Also, some gharials are said to reach similar sizes to the former gators, but never the level of Sarcosuchus.. One noteworthy appearance of Deinosuchus was the fourth The Land Before Time film, in which a cantankerous Deinosuchus appears as one of the two main villains (partnered with an equally disagreeable proto-bird, Ichthyornis), while another was the focus animal of the last episode of Prehistoric Park, wherein Nigel brings one back to the present for his dinosaur zoo — and is considered by him the hardest animal to catch in the whole series, even more than the Tyrannosaurus rex of the first episode. Sarcosuchus appeared in the 2003 miniseries Chased by Dinosaurs, with a rather minor role in the story and incorrectly living alongside Giganotosaurus and Argentinosaurus — basically, its only purpose was an excuse for the programmers was to add another giant reptile for Nigel to meet. Both Deinosuchus and Sarcosuchus reappear in Planet Dinosaur, both with minor roles (and the latter erroneously living alongside Spinosaurus, which actually appeared 10 mya after it went extinct) — useless to say, dinosaurs are the main characters as usual.

1. Entry Time: the 1990s/2000s
2. Trope Maker: The Walking with… franchise and The Land Before Time sequels

Titan Snake and Mega Lizard: Titanoboa & Megalania *

It's not common to see snakes in prehistory media, even documentaries; but in recent years, Titanoboa cerrejonensis ("Cerrejon's titanic boa") has been gaining in popularity.

This huge snake was found only in 2009, and lived in the swamps of Paleocene Colombia just a few million years after the extinction of the nonbird dinosaurs. It was one of the top predators of its world (unlike the famous bird Gastornis, which recent research indicates was a herbivore), hunting huge fish and crocodiles. Although it was not as big as sometimes reported ("only" one or two meters longer than the biggest green anacondas or reticulated pythons), Titanoboa was more heavily-built, and may have weighed an impressive 1 ton; green anacondas reach 200 kg at the most, reticulated pythons slightly less so. Despite the early period at which it lived, Titanoboa was part of the same family as modern boa constrictors and anacondas, and like them, it probably preserved vestigial hindlimbs in the form of small "spurs". As a constrictor, it was not venomous, and it probably gave birth to live offspring as all boas and anacondas do (pythons lay eggs and take care of them by coiling around them).

Megalania ("big tearer") has been known far longer; it was described by Richard Owen (the dinosaurs' Trope Namer) in the 19th century. It was a type of monitor lizard, extremely closely related to modern goannas and Komodo dragons, to the point that in 2004, it was put in the same genus as modern monitors, Varanus, after spending nearly a century-and-a-half as its own genus, "Megalania" prisca (and thus renamed Varanus priscus^note the change to the species name was to comply to the Latin rules of grammar, as Varanus is masculine and "Megalania" is feminine); Megalania still remains in use as a common informal name for it though. It was one of the top predators of Ice Age Australia, in competition with the marsupial lion Thylacoleo (see below) and some land-dwelling crocodilians (the Mekosuchines). Megalania is the largest-known fully terrestrial lizard of all time, but due to the lack of complete or near-complete skeletons, its exact size is controversial (estimates range between 10-25 feet long; pop-media tends to exaggerate it). Its behavior was arguably similar to that of modern goannas, and like them, it had a snake-like forked tongue to detect odors from the soil, laid eggs, and was likely an intelligent animal with complex behavior. We don't know, however, if it was venomous like the Komodo dragon, but if it was, it would have been the largest venomous animal ever. Megalania went extinct only a few thousand years ago, along with most of the Australian megafauna, at about the same time as the extinction of the mammoths and sabertooths; it may have been killed at least indirectly by the fires created by the first prehistoric human colonizers of the Land Down Under.

1. Entry Time: the 2000s for Megalania and 2010s for Titanoboa
2. Trope Maker: Monsters We Met (Megalania), Primeval: New World (Titanoboa)

Other extinct modern reptiles

Sorry, these aren't here. If you're looking for Protosuchus, Goniopholis, Kaprosuchus, Colossochelys, Meiolania, Homoeosaurus, Bavarisaurus, Gigantophis, Dinilysia, and others, see here.

Primitive Reptiles in Media

Crocodiles or Dinosaurs?: the "Thecodonts" **

"Thecodont" ("teeth in sockets") is a now-abandoned term (at least in cladistics) for basal archosaurs and their close relatives that were neither dinosaurs, nor pterosaurs, nor crocodilians. They were all from the Triassic, and were the real dominant reptiles of this geological period, to the point that dinosaurs are often quoted as their natural successors in the following Jurassic and Cretaceous periods. However, at least initially, they were in competition with Triassic mammal-ancestors. Many "thecodonts" went extinct at the mass extinction at the end of the Triassic: the latest ones lived alongside the first dinosaurs like Coelophysis and Plateosaurus, but others went extinct earlier.

The most striking ones were perhaps the giant rauisuchians^note who may not be a natural grouping, but a miscellany of similar-looking reptiles of the Late Triassic, because they were theropod-like predators, top carnivores lording over the first carnivorous dinosaurs. Walking with Dinosaurs popularized one of them, the North American Postosuchus ("Post's crocodile", after a town in Texas), which shared its environment with Coelophysis; depicted as a quadruped in that show, it's now believed to have been bipedal. Another noted group were the herbivorous, heavily armored aetosaurs, with the North American Desmatosuchus being the most famous, due to its impressive shoulder spikes. There's also the aquatic and extremely crocodile-like phytosaurs, who are most easily distinguished from modern crocodiles by how their nostrils are positioned just in front of their eyes, like a whale's blowhole; the most-often portrayed phytosaur is Rutiodon. Both the aetosaurs and phytosaurs were also often of large size and lived in the Late Triassic (Desmatosuchus' was in fact a contemporary of Postosuchus and Coelophysis'', but sadly missed out on appearing in WWD). Rauisuchians and aetosaurs were more closely related to crocodilians than to dinosaurs and pterosaurs, together forming with the crocodilians one of the two main lineages of the archosaur family tree, Pseudosuchia (the other is Ornithodira, which contains birds and nonbird dinosaurs, pterosaurs, and their ancestors). Phytosaurs, on the other hand, were long believed to be direct crocodile ancestors, but are much more basal ("primitive") animals just outside of the true archosaurs. All of them are sometimes wrongly presented as true crocodiles in media.

The start of the Triassic presented a wholly different set of "theocodonts" in the form of the protersouchids, and later the erythrosuchids. The former group, named after their archetypal and most famous member Proterosuchus (also known as Chasmatosaurus), had uncinated upper jaws like some dinosaurs like Dilophosaurus or Spinosaurus; the first large predators to emerge after the Permian Mass Extinction, they are traditionally thought of as semi-aquatic ambush predators, but may have been terrestrial. Meanwhile, the erythrosuchids, who replaced the proterosuchids as top predators a few million years later, are distinguished by their disproportionately huge heads and their forward-pointing eyes; the namesake of this group was the South African Erythrosuchus. Many of these early carnivorous "thecodonts" were as large as many modern crocodilians. Both of these groups were extremely primitive relatives of the true archosaurs — quasi-archosaurs, if you will.

Perhaps the most common "thecodont" in popular dinosaur books and documentaries has been Euparkeria, often wrongly cited as an ancestor of the dinosaurs because of its partially bipedal shape (in reality, it was a much more primitive animal, much like the phytosaurs, proterosuchuids, and erythrosuchids). Just 3ft long, this small reptile lived in the Early Triassic of South Africa alongside the aforementioned Erythrosuchus, as well as other much larger "theocodonts", mammal-ancestors, and giant amphibians (some of whom likely ate Euparkeria for breakfast).

The even smaller Lagosuchus, only one foot long, and thus called "rabbit-croc", was an actual ancestor of dinosaurs, but it lived in Middle Triassic Argentina. In fact, some sources have even wrongly classified it as "the first dinosaur" when it actually lived just before the appearance of the first true dinosaurs. It may have had some feather-like or hair-like structures in its body, like the related pterosaurs and dinosaurs, but this cannot be proven at the moment. Some slightly larger specimens of Lagosuchus have been classified as their own animal called Marasuchus, but the validity of the latter has been debated.

Before the discovery of Lagosuchus in the 1970s, other "thecodonts" were considered the direct ancestors of dinosaurs, especially the European Saltoposuchus and to a lesser degree Scleromochlus^note The latter could be an ancestor of pterosaurs, though. — and some were often even considered early proper dinosaurs (more precisely, early theropods), notably the 12ft long Ornithosuchus, the 2ft long Saltopus, and the 20ft long Teratosaurus. It is now understood however that Ornithosuchus, Teratosaurus and Saltoposuchus were Pseudosuchians; Teratosaurus was in fact a rauisuchian like Postosuchus above — Saltopus meanwhile was an Ornithodiran just like Lagosuchus, a dino-ancestor but still not a true dinosaur.

1. Entry Time: undetermined
2. Trope Maker: Popular dinosaur books and other media

Giant Neck and Scissor Beak: Tanystropheus & Hyperodapedon *

These guys were among the oddest and most specialized reptiles ever, despite their smaller size compared to many other reptiles of the Mesozoic. They were primitive archosaur-relatives, just like Euparkeria, Rutiodon, Proterosuchus, and Erythrosuchus, but unlike them, they have never been considered "thecodonts", not even in the past. Both lived in the Late Triassic around the same time the first dinosaurs appeared.

Tanystropheus was 6m long and notable for its enormously long neck compared with its shorter body and tail, to the point that it could be mistaken for a plesiosaur at a glance. Its neck was proportionally even longer than a classic plesiosaur or a typical sauropod (the neck alone made up half of the animal's entire length!), and was made by a few extremely long vertebrae that made it stiff. Once, the neck and the rest of the body were believed from two distinct animals! But the Tanystropheus had true legs (with longer hind legs than front legs), not flippers like the plesiosaurs, making it looking like a lizard with a giraffy neck. It was probably amphibious and a hunter of small aquatic prey, but its hunting style is unknown; some think it swam in the ocean after fish, others think it stayed on land to snatch food from the shoreline with its extraordinary neck. Once considered a plesiosaur ancestor, Tanystropheus actually belonged to its own group of archosaur-relatives called the protorosaurs. Tanystropheus had a notable appearance in Sea Monsters, where it is shown losing its tail like many modern lizards do, after Nigel Marven grabbed it by the tail. This was based on a theory suggested by one scientist who pointed to certain fractures on the tail similar to those seen in lizards that do this. However, no other studies have found support for this idea, putting it entirely in the realm of fiction.

Hyperodapedon was very different: it was an herbivorous land reptile belonging to a highly successful group of archosaur-relatives known as rhynchosaurs. Curiously, the rhynchosaurs were once considered relatives of the modern tuatara, which is in fact a cousin of snakes and lizards. Hyperodapedon (also called Scaphonyx or Paradapedon) is the most frequently portrayed of its group in paleo-art because of its strange owl-like face: it had eyes pointing forwards just like an owl, and most notably, an uncinated beak with a split in its upper half that the lower half fitted into when the mouth was closed ("rhynchosaur" means "beak lizard"). This reptile and its fellow rhynchosaurs have usually been described as sluggish critters unable to flee the faster predators of the time like the rauisuchians and the first meat-eating dinosaurs, but this might not be true: the rhynchosaurs' short, splayed limbs and bulky body don't mean they were slow and harmless, and their parrot-like bill was powerful enough to deliver nasty bites to its attackers, like the beak of a modern macaw or snapping turtle.

1. Entry Time: Undetermined
2. Trope Maker: Popular dinosaur books and other media

Gliding Lizards: Kuehneosaurus, Coelurosauravus, & Longisquama *

Kuehneosaurus latus from Late Triassic Europe, and Coelurosauravus elivensis (also called Daedalosaurus'') from Late Permian Madagascar were much smaller than the two reptiles above, just a few feet long, but both deserve the popular nickname of "gliding lizards" — the former was even a distant cousin of lizards, the second a basal diapsid.

Kuehneosaurus had elongated, protruding ribs that pointed sideways from the body, while Coelurosauravus had rod-like projections growing out from the sides of its body. In both animals, these strange bones were connected by skin like the famous Dimetrodon sail, forming wings for gliding from one tree to another. Today, a modern true lizard has convergently evolved a similar gliding mechanism, the so-called "flying dragon" of southeast Asia, although its "wings" are made from enlarged ribs. Kuehneosaurus had a contemporary relative in North America called Icarosaurus, while Coelurosauravus had a contemporary European relative called Weigeltisaurus, which was once considered the same animal. Both Coelurosauravus and Weigeltisaurus also had tiny frills like those of Triceratops (minus the horns). A Coelurosauravus named Rex appears in the TV series Primeval as the chaacters' Team Pet, although the animal is slightly oversized from its real-life counterpart, can actually fly rather than just glide, and has a fleshy crest in place of a bony frill.

The Middle Triassic Longisquama means "long scale": its classification has long been a headache for paleontologists, flip-flopping between a relative of Kuehneosaurus, an archosaur-relative, and an extremely basal diapsid. Also a few feet long like Kuehneosaurus but found in the former USSR in The '70s (in modern Kyrgyzstan), its most famous quality is its eponymous "long scales" — a single row of tall, hockey stick-shaped appendages growing from its back. These crazy scales have utterly baffled scientists from their discovery, to the point that some think they're just plant fronds that fossilized with the animal when it died. It was once believed Longisquama had two rows of these growths on its back, leading some to suggest it was a gliding creature, using the "long scales" to cross the air like a modern flying squirrel; nowadays, we think it used the singular row of weird scales for display, but even this is not certain. Because its huge protrusions resemble feathers a bit, it was even believed to be an ancestor of birds in the past. Another "gliding lizard", the only one known with bat-like skin-membranes, was Sharovipteryx ("Sharov's wing"), which lived in the same time and place as Longisquama. This one was hypothesized in the past to have been the ancestor of pterosaurs, but astonishingly, was actually most closely related to Tanystropheus. Longisquama appears in Disney's Dinosaur as a sort of flying chameleon using its scale-things as the feathers of actual wings (clearly drawing inspiration from some of the outdated hypotheses mentioned above).

1. Entry Time: Undetermined
2. Trope Maker: Primeval (Coelurosauravus), Dinosaur (Longisquama)

Swimming Reptiles: Nothosaurus, Placodus & Champsosaurus *

These reptiles are mostly unified by the fact that were aquatic but less specialized than the classic marine reptiles within the main folder above. They were also usually smaller-sized than them.

Hailing from the Late Triassic, Nothosaurus ("false lizard") looked a bit like Tanystropheus, but its neck wasn't as excessively long, and it was actually related to the ancestors of plesiosaurs and pliosaurs. Like the long-necked plesiosaurians, Nothosaurus had needle-like teeth set in elongated but weak jaws; unlike plesiosaurs, it had a well-developed tail for swimming by undulating like a mosasaur, and short, splayed true legs with palmated feet. Because of the latter feature, it and the other nothosaurs have often been portrayed as sort of like seals or sea otters of the Triassic, coming onto land to lay their eggs but feeding with agility in the water on fish and shellfish. Another marine reptile, the Middle Triassic Askeptosaurus was outwardly similar to a nothosaur, but belonged to a more archaic group: the Thalattosaurs (lit. "sea lizards"), whose relationships with other reptiles are uncertain (they've been various placed as relatives of ichthyosaurs, archosaurs, lizards/snakes, and plesiosaurs/pliosaurs/nothosaurs).

Hailing from the Early Triassic, Placodus was the namesake of the Placodonts, a highly unusual group of marine reptiles related to the nothosaurs, plesiosaurs, and pliosaurs. Placodus looked a bit like a marine iguana, but was much more massively-built, with dense bones for clinging onto the seabed and powerful short jaws with flat crushing teeth for eating shellfish. If Nothosaurus was the seal of the Triassic, then Placodus was the walrus of its day. Like Nothosaurus, it probably came onto land to lay eggs and swam using its strong tail and webbed feet. Placodus ("plate-tooth") also had light armor consisting of a line of bony plates running along its whole backbone. In the most derived placodonts like Henodus, said armor had developed into literal shells, making them very turtle-like (a classic case of convergent evolution).

Mixosaurus was one of the most primitive ichthyosaurs, also from the Early Triassic. It had already the classic head, neck and body of the more known/derived Ichthyosaurus, but its tail fin was still small, because the vertebrae of its tail don't show the downward bend of the derived ichthyosaurs. Smaller than Ichthyosaurus (some individuals were only 1m long), Mixosaurus might recall an ichthyosaur with a mosasaurian tail, or even a tiny mosasaur that looked like a dolphin.

Champsosaurus lived much later than the above reptiles in the Late Cretaceous, and unlike them, it was a freshwater animal. It belonged to a particular lineage of archaic reptiles known as the Choristoderes, whose exact relationships with other reptiles are uncertain. Champsosaurus lived in North America, first appearing about 76 mya and making it the end of the Cretaceous to see T. rex and Triceratops 66 mya. Unlike them, Champsosaurus survived the great dinosaur extinction, and went on to see the rise of the mammals, only to go extinct shortly afterwards during the Paleocene. Champsosaurus greatly resembled a true crocodilian (its name means "croc-lizard"), with Cretaceous specimens being about 1.5m long and Paleocene ones being up to 3m. It is sometimes is wrongly portrayed in documentary media as a true crocodilian, but it would have lacked the armor seen in real crocs. Its slender snout tell us it was a fish-specialist, leaving larger prey to the true crocs it often shared its environment with.

True crocodiles (not quite; see later), on the other hand, were the Late Jurassic Metriorhynchus, Geosaurus, and Teleosaurus, which are here for comparison, but should more correctly be put together with Deinosuchus and Sarcosuchus above. Unlike the mostly freshwater modern alligators and kin, they adapted to a fully marine lifestyle, hence their proper name, the Thalattosuchians ("marine-crocs" or "sea-crocs"). Unlike Deinosuchus, but like Sarcosuchus, they were too primitive to be considered part of the modern order of crocodilians and should technically be considered crocodile-relatives or crocodiles in only the broadest sense of the term. Metriorhynchus ("moderated snout" because of its thin jaws) and the very similar Geosaurus are both known from Europe: they have lost their armor altogether, developed a caudal fin very similar to an ichthyosaur's, and have limbs similar to paddles, though still not proper flippers like those of a plesiosaur or sea turtle. At 3 meters, neither is the largest of their group; some of their relatives could reach over 6 meters. The thalattosuchians first appeared in the Early Jurassic about 190 mya, but became extinct in the Early Cretaceous, 125 mya. Another thalattosuchian was the Middle Jurassic European Teleosaurus a more archaic sea-crocodile, resembling a small gharial in shape: it still had a light body armor, weak but still land-adapted legs, and a regular crocodilian tail. Some sculptures of it are portrayed in the Crystal Palace Park of London together with other more famous Mesozoic reptiles — unusually, still accurate today.

1. Entry Time: Undetermined
2. Trope Maker: Popular dinosaur books and other media

Early Reptiles?: Scutosaurus, Mesosaurus & Hylonomus *

When discussing the origin of amniotes, the clade consisting of true reptiles, birds, true mammals, and mammal-ancestors, the first amniotes to appear on Earth are usually and traditionally called "reptiles". But the animals in this section, according to many experts today, cannot be classified among either the diapsids (all modern reptiles, dinosaurs, and birds) or the snyapsids (mammals and their ancestors). The first two are placed in a group called the parareptilians — traditionally called anapsids — because they were within the reptile class, but were the sister group of the diapsids, and thus not related to any modern reptiles. It's worth noting that for a long time, turtles were considered parareptilians as well, but today are believed to be diapsids, possibly related to plesiosaurs or even archosaurs.

Scutosaurus means "shield lizard", and was once considered an ancestor of turtles. It was one of the biggest and most heavily-armored parareptilians ever, weighing 1 ton (comparable to a bison) and covered with armor on its back — recalling more an Ankylosaurus than a tortoise. Like the armored dinosaurs, it was a vegetarian; it had a thickened skull and blunt teeth all similar to each other; its limbs were semi-erect and stocky; and the tail was very short. It belonged to a group of parareptilians called the pareiasaurs, named after their archetypal member Pareiasaurus, which was similar but without the armor. Both lived in the Late Permian in Russia and South Africa, respectively, and were among the animals wiped out by the gigantic mass extinction that separated the Permian from the Triassic — the worst to have happened since multicellular organisms evolved, even more destructive than the one that ended non-avian dinosaurs.

The much smaller (2ft long) Mesosaurus has a deceptive name: it was not related at all with the much more famous Mosasaurus — the former name means "middle-lizard", the latter "lizard from the Meuse River" (in the Netherlands). Despite this, Mesosaurus did somewhat resemble in shape the old classic illustrations of mosasaurs, being elongated, with long toothed jaws, and a powerful sideward-undulating tail for swimming. But its legs were apt for walking, like modern crocs and unlike the paddle limbs of its almost-namesakes mosasaurians (the mesosaur's limbs were palmated-footed at the most). This makes Mesosaurus actually more similar to Nothosaurus or Champsosaurus than to a mosasaurid. Like Champsosaurus, it's sometimes mislabeled in paleo-media as a crocodile-ancestor, or worse, a true crocodilian. In reality, Meosaurus lived in the Early Permian, disappearing long before the ancestors of crocodiles evolved. Adapted for freshwater or estuarine/coastal life, Mesosaurus was one of the first vertebrates to re-evolve an aquatic lifestyle and return to the water. Mesosaurus' numerous tiny, needle-like teeth were adept at catching small fish, but it was too small and ill-adapted for life in the open ocean. But because its fossils are known from both Africa and South America, it was one of the main fossils used as evidence for the existence of Pangea (alongside the mammal-ancestors Cynognathus and Lystrosaurus (see below) and the plant Glossopteris).

Hylonomus, similar to a 1-foot-long lizard, is still today considered the first undisputable reptile, hailing from the Late Carboniferous of Canada about 312 mya. Hylonomus was long considered a parareptilian, but today is mostly classified as a diapsid relative, thus belonging to a different lineage than Scutosaurus and Mesosaurus above. It's also famous because many skeletons of it have ben found in hollowed-out petrified stumps: it could have fallen into them and gotten trapped (or drowned if they were full of water). Two competitors for the "first reptile" title popped up in the 1990s. The first, Westlothiana (from the Early Carboniferous of Scotland, 338 mya), seemed to take the record over from Hylonomus (earning it the nickname "Lizzie" in the media), but is now mostly considered a very reptile-like "amphibian" (sensu lato). The other, Casineria (about the same age as "Lizzie" and also Scottish), is much more heavily contested as its sole, fragmentary fossil shows affinities with amphibians and may in fact represent a transitional form between reptiles and their ancestors.

1. Entry Time: Undetermined
2. Trope Maker: Popular dinosaur books and other media,

Other primitive reptiles

Sorry, these aren't here. If you're looking for Trilophosaurus, Drepanosaurus, Megalancosaurus, Helveticosaurus, Hupehsuchus, Shringasaurus, Claudiosaurus, Procolophon, Elginia, Milleretta, Captorhinus, and others, see here.

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Mammal-Ancestors

At least pterosaurs and the above-mentioned seagoing and terrestrial animals are mainly from the same time period, the Mesozoic. Don't even get us started on how non-mammalian synapsids (the "mammal-like reptiles") are sometimes labeled dinosaurs, even though the most famous of them lived far earlier, in the Late Paleozoic.

Mammal-Ancestors in Media

Most non-mammalian synapsids lived well before the appearance of the first dinosaur during the Permian period (just before the Triassic); indeed, non-mammalian synapsids were the very first large land vertebrates and diversified much during their time on Earth, until most of them were wiped out in the huge Permian mass extinction. In the new world that followed, the few surviving species were progressively outcompeted by archosaurs, the group containing dinosaurs, pterosaurs and crocodilians. The last kinds were depleted at the end of the Triassic in another mass extinction, with their true mammalian descendants continuing their legacy. They are traditionally divided into the more derived therapsids and the more basal "pelycosaurs", with mammals technically being members of the former group in the same way birds are theropod dinosaurs. Although popularly called "mammal-like reptiles", they're not related to any reptiles living or extinct and should be more properly called proto-mammals or mammal-ancestors.

Anyway, all these creatures have extraordinary relevance to the history of evolution because they were the ancestors of true mammals and thus of mankind, and yet they've usually never had the popularity of the dinosaurs, probably because of their relatively small size compared to dinos like T. rex or the sauropods.

Stock Mammal-Ancestors

Sail-Backed Lizard or Sail-Backed Mammal?: Dimetrodon ***

Dimetrodon lived in North America 280 million years ago, in the Early Permian. It is the only proto-mammal whose popularity matches that of the stock dinosaurs, thanks to the mohawk-esque crest (named "sail" because of its shape) on its back. Its iconic status among proto-mammals is partially justified by its fossil abundance — dozens of specimens are known, juveniles included. As one might expect at this point, it was discovered in North America during the Bone Wars in the second half of the 19th century.

The most classical of its numerous known species is, needless to say, one of the biggest and first discovered, Dimetrodon limbatus, 3-4m/10-12ft long and weighing about 300 kg, like a small gator or a large deer. Other species were much smaller, some only 2 feet long. Being a very early mammal-ancestor, it was not a proper therapsid, but rather one of the so-called "pelycosaurs". It still had a lizardy shape, with a long tail, a long body, splayed legs, and a skull with a small braincase. Fossil prints show a lizard-like gait. Other traits, on the other hand, were quite mammalian: a laterally-flattened trunk, not wider-than-taller like most modern reptiles; a solid skull with one single pair of temporal openings placed near the maxillary hinge (the so-called "synapsid" condition also seen in mammals, humans included); and differently-shaped teeth — Dimetrodon just means "teeth of two lengths." Even though all its teeth were conical, the anterior ones were small and crammed together like incisors, while the longest teeth were in the place mammals have usually their canines. Behind them, the posterior teeth were small and not apt for chewing food unlike our molars, but are somewhat analogous to those seen in primitive insectivorous mammals. More derived mammal-ancestors like Cynognathus or Thrinaxodon achieved a clearly mammalian anatomy, with more erect limbs, shorter tails, larger brains, and teeth very similar to mammals.

Its "sail", sustained by elongated vertebral spines, has always been a headache for scientists. The classic theory considers it a thermoregulating device. Turned to face the solar rays, it could have captured heat like a solar panel; turned parallel to them, it would have been more like a radiator, dispersing heat. Other theories are mating or threat display, inter-specific identification, and so on. It may have been that the sail served all these purposes. Among external features, Dimetrodon is sometimes depicted as having fur, external ears, or even milk glands, but given its primitiveness, these are extremely unlikely. The coloration is totally speculative — its sail could have been vividly colored and/or able to change colors for display purposes. Some scientists believe skin might not have covered the sail that extensively, leaving the bony tips jutting out. No eggs or nests are known from Dimetrodon; we don’t even know if it was oviparous (an egg-layer), or viviparous like modern mammals (though if the latter, it evolved viviparity independently, as monotremes like the platypus and echidnas being oviparous suggests viviparity in the mammal lineage is posterior to the first true mammals).

Dimetrodon was probably the top predator of its time and one of the first large terrestrial predatory vertebrates, shown in paleo-art hunting early amphibians like Eryops, Diplocaulus, and Seymouria; fish; and what could be called its Non-Identical Twin, Edaphosaurus (see below). Its crest, its deceptively reptilian appearance, and the fact that it was a large carnivore make Dimetrodon a predestined victim of Dinosaurs Are Dragons and Prehistoric Monster both in fiction and in docu-media. However, if you put it next to other famous prehistoric animals, Dimetrodon would appear rather narmy. If we imagine a battle against a Tyrannosaurus, Deinosuchus, Smilodon or Mosasaurus, the primitive and relatively small dimetrodont would always be the loser — this might also be true if it were pitted against modern predators (lions, tigers, Kodiak bears, polar bears, Nile crocodiles, great whites sharks, killer and sperm whales, etc.), as well as most ancient and modern giant herbivores, like the multi-ton sauropods, elephants, mammoths, trikes, stegos, rhinos, hippos etc. Its weakest point, other than the primitive gait, would be its blood-vessels-rich membranous sail, bleeding copiously to death if ripped off by its animal adversary. But in the Early Permian swamps it called home, Dimetrodon was still the fiercest and most powerful carnivore of its time, definitively debunking the Narm thing.

Although Dimetrodon is more closely related to you than to any dinosaur, and predated the first dinosaur by at least a country mile of geologic time, it is often mixed with dinosaurs in toy collections just because it looks cool. In movies and comics, it may even show up living with cavemen. Expect it to look like a giant iguana with scaly skin. Actually, scales are strictly a reptilian and avian thing, and Dimetrodon hide was probably naked like modern hairless mammals, with some hardened fish-like belly scales left over from its amphibian ancestry. Its shape makes Dimetrodon the most abused animal within the Slurpasaur trope. For example, in the 1970 film version of Journey to the Center of the Earth some Caribbean iguanas with ridiculous crests on their backs live-act Dimetrodons, which of course attack the humans.

1. Entry Time: 1940s
2. Trope Maker: Fantasia, The Age of Reptiles and in turn the Prehistoric Dinosaur Playset from Louis Marx and Company

The Dimetrodon's Vegan Cousin: Edaphosaurus *

After Dimetrodon, Edaphosaurus is the only "pelycosaur" which has some chance of appearing in non-documentary media — at least indirectly: sometimes Dimetrodons with a sail more similar to Edaphosaurus are seen in fictional works, ex. in The Land Before Time.

Described by Cope during the Bone Wars from the Early Permian Red Beds of Texas (Dimetrodon was also first described by Cope from the same geological terrains), Edaphosaurus means "pavement lizard" in reference to its teeth, which are packed together like the tiles of a floor. Like Dimetrodon, several species are known, from less than a foot to over 11 feet in length . Edaphosaurus was bulkier-bodied and smaller-headed than the very similar Dimetrodon, sharing its carnivorous cousin's back sail, long tail and splayed legs. Its sail was more complex however: it had a more rounded shape and regularly-placed tubercles of uncertain purpose. Contrasting the pointier, more varied teeth of Dimetrodon, Edaphosaurus had round, peg-like teeth all of the same shape and length. Its dentition, along with its large gut, tells us that it was a plant-eater — in fact, it was one of the first large terrestrial vertebrate herbivores to evolve. It's also hypothesized to have eaten shellfish as a dietary supplement.

Living alongside Dimetrodon in the swamps of Early Permian North America, it probably used its "sail" the same way as the former (whatever way that was), but obviously this cannot be known for certain. Edaphosaurus is sometimes shown in paleo-art, books, and programs like Walking with Monsters as one of Dimetrodon's possible prey. This might be plausible (Edaphosaurus was arguably a slower runner), though if so, Dimetrodon almost certainly hunted young Edaphosaurus more often than the massive adults.

1. Entry Time: undetermined
2. Trope Maker: its resemblance with ''Dimetrodon'

More Dogs than Reptiles: Cynognathus & Thrinaxodon **

If you've seen Cynognathus in an illustration, you probably thought at least once "Oh, this thing looks like a big dog!" Cynognathus ("dog jaws"), unlike Dimetrodon, was a true therapsid, belonging to the therapsid subgroup called the cynodonts ("dog teeth"). These were the most advanced and mammal-like of all the mammal-ancestors, with a very mammalian look, certainly at least some hair and quasi-mammalian dentition. They were also among the smallest therapsids, being mostly cat-sized; even Cynognathus, the largest known, was still no bigger than a German Shepherd.

Found in South Africa at the end of the 19th century, Cynognathus crateronotus (its only known species) has traditionally been considered the archetypal cynodont and, more generally, the archetypal therapsid in documentary media. It has been cited as one of the unofficial symbols of evolution, as one of the "missing links" between reptiles and mammals (just like Archaeopteryx, the "missing link" between reptiles and birds), even though it wasn't really a reptile. As its fossils are also known from Argentina and Antarctica, it was also one of the key fossils used to argue for the Pangea hypothesis.

Despite this, Cynognathus has not received much attention outside non-fictional works, maybe due to being not so impressive-looking compared with Dimetrodon or, naturally, dinosaurs. However, it is very common in popular prehistory-related media as the most classic example of a particularly mammalian-looking therapsid, typically described as "dog-like" and/or "wolf-like", in contrast with the primitive "lizard-like" Dimetrodon (which more often tends to be considered a dinosaur because of this). Cynognathus is also often portrayed as an excellent predator, and in Real Life, it may have been as powerful as Dimetrodon in spite of its smaller size (it was about half the length of D. limbatus), possibly even capable of killing therapsids bigger than itself, like the herbivorous dicynodonts — don't confuse them with cynodonts: they were two distinct lineages of therapsids, and dicynodonts were less close to mammals than cynodonts. We don't know if Dimetrodons and Cynognathuses were pack hunters or solitary hunters, nor if they were ambush-killers or active pursuers. But unlike Dimetrodon, Cynognathus was not the apex predator of its day; in Early Triassic South Africa, it lived alongside the huge predatory archosaur-relative Erythrosuchus.

Even though it was almost certainly hairy, Cynognathus' fur would have been less dense than modern mammals. Unlike Dimetrodon, Cynognathus has never been portrayed with scaly hide; at most, it's given just naked skin. We don’t know if Cynognathus and other cynodonts had external ears or mammary glands (two distinctive mammalian traits), but the odds they had them were obviously far greater than the primitive Dimetrodon. Like the latter, we have no idea how Cynognathus was colored. Media tend to depict cynodonts like it and Thrinaxodon (and other carnivorous therapsids like the apparently-similar but more primitive gorgonopsians) with a brown color scheme, but this might not have been the case in Real Life. The usually-bland coloration typical of mammals is thought to be an adaptation for darkness — according to scientists, every modern mammal (even diurnal ones, like us humans) descend from night-dwellers. Nocturnal habits, however, developed within the synapsid lineage only in the Triassic, to avoid competition with dinosaurs (or at least, that’s what most scientists say). If true, this would mean non-mammalian therapsids like Cynognathus could have been very colorful, like many modern reptiles and birds.

After Cynognathus, the most represented among the Cynodonts is the cat-sized Thrinaxodon liorhinus: it was the basis for the unidentified cynodont species that appeared in the first episode of Walking with Dinosaurs. Also found in South Africa at the end of the 19th century like the cynognath, Thrinaxodon ("trident tooth") has sometimes been cited as "the most mammal-like among mammal-like reptiles": but recent research indicates it was actually one of the most basal cynodonts, even more basal than Cynognathus itself. With its small size, compact body, short but robust legs and short tail, it probably lived in self-dug burrows like a modern badger, and could have been a hunter of small animals, again much like a badger. It lived just after the Permian mass extinction at the very start of the Triassic and just before Cynognathus showed up; it's likely its burrowing habits helped its ancestors survive the Permian extinction. Careful analysis of its skull shows the thrinaxodont was definitely covered in fur and also had sensitive whiskers, just like modern mammals. Given that Cynognathus was even closer to mammals than Thrinaxodon was, the former too should have had thus fur and whiskers.

1. Entry Time: undetermined (Cynognathus), 1999 (Thrinaxodon)
2. Trope Maker: Popular prehistory media (Cynognathus), Being the basis of the cynodont from Walking with Dinosaurs (Thrinaxodon),

Only Two Teeth: Lystrosaurus & Placerias *

Dicynodonts ("two dog-like teeth") were the most diverse group of mammal-ancestors, living from the Late Permian up to the very end of the Triassic (an alleged Early Cretaceous fossil turned out to be a misdated and misidentified Pleistocene marsupial). They were very varied in size and shape, but all were herbivorous and shared very specialized dentition: they had only two teeth in their upper jaw and no teeth in the lower one, coupled with a tortoise-like beak in front of the teeth. We don't know if they had some hair or were still totally naked.

The most iconic dicynodont is probably Lystrosaurus ("shovel lizard"). Others include the classic Dicynodon (see below), the small burrowing Diictodon of Late Permian Africa, the large kannemeyeriiforms like Kannemeyeria of Early Triassic Africa and Placerias, and the most spectacular of them all, the elephant-sized Lisowicia found only in 2019 — the latest one is currently the biggest known therapsid by far (again, see below).

One of the first animals to have recuperated after the Permian-Triassic extinction event, Lystrosaurus was one of the most successful animals of all time; '95% of all land vertebrates alive at the start of the Triassic were Lystrosaurus. Its remains have been discovered everywhere in southern continents, even Antarctica (don't forget that this continent began to freeze only a few million years ago). Thanks to this, Lystrosaurus is one of the classic fossils used to prove the Pangaea supercontinent hypothesis, like Mesosaurus, Cynognathus, and the plant Glossopteris. The size of a medium pig and thus bit bigger than Cynognathus, Lystrosaurus has the typical dicynodontian shape: bulky, stubby-tailed, with strong semi-erect limbs, and the typical dentition made up of only the two upper tusk-like "canines". Formerly, it was depicted as a freshwater dweller like a hippo, but now is mostly believed to have been a grazing land animal. In paleo-art, it is often shown as the favourite prey of Cynognathus, but in reality, Cynognathus lived slightly later than Lystrosaurus — Cynognathus instead lived alongside the aforementioned Kanneyemeria, while Lystrosaurus coexisted with Thrinaxodon.

In Walking with Monsters, Lystrosaurus is shown as very similar in behavior to modern wildebeest, living in immense noisy herds, crossing a river in a mass, and dying by drowning or being killed by Proterosuchus (under its old name of Chasmatosaurus and depicted as a semiaquatic crocodile-like hunter rather than the terrestrial animal many believe it is today). Lystrosaurus also appeared in Jurassic World Dominion, along with Dimetrodon, making them the first proto-mammals to appear in the franchise.

Placerias hesternus was from the same habitat of Coelophysis, Postosuchus, and Desmatosuchus in Late Triassic southern USA. It was bigger and more evolved than Lystrosaurus, weighing 1 ton and with a body-shape rather similar to the herbivorous dinocephalians like Moschops (see below) or pareiasaurs like Scutosaurus. Its very large head was typical of a dicynodont however, with only two upper teeth and a round tortoise-like beak. Its most striking feature is the shape of its teeth: instead of protruding downwards like most other dicynodonts, they pointed forwards like short tusks. Its time and place were depicted in the first episode of in Walking with Dinosaurs, with Placerias appearing as a prey animal to Postosuchus. In the show, it and Postosuchus are represented as particularly slow animals, but experts think they were much nimbler in reality. Its tusks also would have been probably powerful weapons against hungry Postosuchus; in WWD, the female Postosuchus that hunts them is wounded by their tusks, crippling it and ultimately leading to its demise by starvation.

1. Entry Time: 2000s (both)
2. Trope Maker: Walking with… (both)

Hulky Beasts: Moschops & Lisowicia *

Moschops ("calf's face") is the most famous member of a peculiar subgroup of basal therapsids known as the Dinocephalians, "terrible heads". These quadrupeds were much more primitive than the cynodonts and dicynodonts, but were extremely varied in lifestyle, including both herbivores and carnivores — all of them were the among largest land animals of their day. Moschops itself was actually one of the biggest among all mammal-ancestors (9ft long, the size of a small rhino), making even the biggest Dimetrodon species small in comparison — but it was still much smaller than the most popular dinosaurs. Its carnivorous cousin and contemporary Anteosaurus was even more massive at 16ft, possibly the largest of all Permian land animals and likely the biggest proto-mammal until Lisowicia (see below) appeared/was discovered.

Moschops capensis (the name of the classic species) was characterized by powerful front legs longer than its hind legs: this, combined with its massive chest and short but muscular neck, gave to it a rather Hulk-like frame. It also had partially splayed front limbs, more erect hind limbs, and a short but well-developed tail. Although not very visible in a mount or painting, the most specialized trait of Moschops was its thickened skull roof, a bit like that of a giraffe but without the "horns" of the latter (its relative Estemmenosuchus had some horn-like protrusions). Studies indicate the purpose of its hard head was most likely for headbutting rivals or predators, making it sort of an earlier version of the true dinosaur Pachycephalosaurus.

Moschops' teeth were small and blunt, and all rather similar to each other, unlike most other synapsids (Dimetrodon included), but they were enough for taking vegetation of the harsh landscapes it inhabited. It lived in Middle Permian South Africa (hence the species name capensis); some portrayals wrongly show it living alongside Dimetrodon or Cynognathus, but it actually lived in a time period between the two, later than the former and earlier than the latter. Old sources often wrongly depicted Moschops with reptilian scales (a common error with most mammal-ancestors), and even with an erroneous line of reptilian tubercles along its neck, back and tail (a bit like an iguana crest but blunter). We don't know if it had some hair on its body like Cynognathus above or was naked-skinned like a modern rhinoceros. Like the tuatara, it had a "third eye" at the top of its skull; in actuality, a tiny bunch of light-sensitive cells properly called the "pineal eye".

While mostly relegated to prehistory books, Moschops was the star of a British stop-motion animated kids show also called Moschops. The title character was best friends with an Allosaurus named Ally and lived with his Grandfather Diplodocus and Uncle Rex; neighbors included Mr. Icthyosaurus and Mrs. Kerry the Triceratops. As you can tell, it was not the most scientifically vigorous show by any stretch of the imagination, even for a cartoon. Moschops himself didn't even look anything like a real Moschops!. Somewhat more accurate versions of Moschops appear in the video games Carnivores and ARK: Survival Evolved, although both depict it as an extremely skittish omnivore that will run away from pretty much anything.

Described only in 2019 (at the end of The New '10s), Lisowicia bojani was found in Europe, precisely in Poland near the town of Lisowice — hence the name. It's not only the last confirmed dicynodont known, living at the very end of the Triassic (even later than the former record-holder, Placerias), but also the biggest known proto-mammal ever, reaching the size of a modern elephant. It would have been as heavy as the biggest contemporaneous "prosauropods" like Riojasaurus but it was still half the length and height of them because of the absence of the typically long neck and tail of the sauropods and their relatives.

Marking its similarity with an elephant even more, Lisowicia also had erect pillar-like limbs convergent with those of a proper dinosaur or elephant, not splayed like most other mammal-ancestors. It had elephantine feet, and unusually for a mammal-ancestor also almost-lacked external tail, resembling several true mammals in this regard. Lisowicia is destined to gain attention, possibly becoming as common in paleo-books as other more traditional therapsids.

1. Entry Time: undetermined
2. Trope Maker: Popular prehistory media

Proto-Sabertooth?: Inostrancevia *

The gorgonopsians ("monstrous faces"; sometimes called gorgonopsids) were the top predators of the Late Permian, but they were killed off by the huge mass extinction that divides the Paleozoic from the Mesozoic. More slender and usually smaller than the earlier dinocephalians, they are nicknamed "sabertooths" just like their mammalian namesakes; however, their upper canines, though longer than most therapsids, were far less developed than those of a saber-toothed cat. They include the group namesake Gorgonops, the wolf-sized Lycaenops ("wolf face") and Sauroctonus ("lizard-killer") — the first two were African, the last was Russian. The perhaps most famous and often portrayed has been (of course) the largest genus, the tiger-sized Inostrancevia alexandri of Russia, named in 1922 after Russian geologist Alexander Inostrantsev.

Inostrancevia, Cynognathus, and other carnivorous therapsids are often described as looking like dogs; indeed, in modern depictions, this resemblance is even more evident than in the older, more reptilian portraits. As usual for proto-mammals, whether or not the gorgonopsids laid eggs and/or had mammary glands is still unknown. We're also not certain if gorgonopsians had fur; like the dinocephalians and dicynodonts, they might have been too basal to develop hair.

The gorgonopsians' history in pop culture is convoluted. The famous Czech paleoartist Zdenek Burian first depicted a Sauroctonus interacting with some Scutosaurus in one of his old paintings◊, and they have appeared seldomly in educational books. The second Dino Crisis game included Inostrancevia, inaccurately showing it as an armored monster living in volcanoes alongside Jurassic and Cretaceous dinosaurs. The 2007 TV show Primeval made them famous by having Inostrancevia appear as the show's first Monster of the Week and then having it fight and kill a future-evolved flightless, predatory bat in the first season finale. The Walking with... series' 2005 entry Walking with Monsters also included a gorgonopsian that went unidentified in the show but has been confirmed in other material to be Gorgonops (although its size and coexistence with Scutosaurus make it more like Inostrancevia).

1. Entry Time: 2000s
2. Trope Maker: Primeval and Walking with Monsters

The First Known Mammal-Ancestor: Dicynodon *

The first mammal-ancestor ever described was Dicynodon lacerticeps ("lizard-headed two dog-like teeth") in the middle of the 19th century, the time in which Darwin popularized his revolutionary concept of evolution. It was named by Richard Owen, the same guy who coined the word "dinosaur". Dicynodon was the very first mammal-ancestor known to science, but at the time, its mammalian traits were dismissed as a case of convergent evolution and it was instead considered an unusual reptile.

At that time, Darwin's pupil Thomas Huxley (nicknamed "Darwin’s Mastiff") proposed a surprisingly modern hypothesis: that land vertebrates should be divided into two branches instead of the then-traditional Linnaean tripartition of mammals-birds-reptiles. Huxley's proposed lineages were the theropsids ("beast-looking", not to confound with therapsids) and the sauropsids ("lizard-looking"). The former were basically the mammals; the latter were the reptiles (including dinosaurs and birds; over a century before feathered non-avian dinosaurs were known). Since Dicynodon was not thought to be related to mammals at tdhe time, Huxley put it in the "sauropsid" branch. It is for this reason that the proto-mammals were formerly classified/called "mammal-like reptiles" and depicted with reptilian traits. It was not until the start of the 20th century were the so-called "mammal-like reptiles" finally recognized as mammal-ancestors, thanks to the work of noted South African paleontologist Robert Broom. However, the term "mammal-like reptile" continued to stick until the early 21st century when the term "proto-mammal" was coined as a new term for these animals.

Dicynodon lived in Late Permian South Africa, and is the official namesake of the dicynodonts. It was a relatively small animal about the size of a dog, but it had the usual two-toothed dentition of the group. Due to the earliness of its discovery it is also the only mammal-ancestor portrayed in the Crystal Palace Park of London — with oversized upper "canines" and a totally erroneous turtle-shell.

1. Entry Time: 1856
2. Trope Maker: Crystal Palace Park

Other synapsids

Sorry, these aren't here. If you're looking for Ophiacodon, Sphenacodon, Cotylorhynchus, Tapinocephalus, Anteosaurus, Titanosuchus, Robertia, Kannemeyeria, Diictodon, Sauroctonus, Lycaenops, Lycosuchus, Bauria, Ericiolacerta, Traversodon, Massetognathus, Oligokyphus, and others, see here.

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Extinct Mammals

Even prehistoric mammals are sometimes mislabeled dinosaurs. Colloquially, this is also often true of prehistoric amphibians, fish, and invertebrates, as well as existing critters that are considered "living fossils" (coelacanth, tuatara, horseshoe crab, nautilus, etc.). Only birds, whether they went extinct before recorded history or afterward, are not mislabeled when called dinosaurs.

Mammals in Media

Among mammals, those living during the Late Pleistocene Ice Age have classically been the most portrayed, because they lived alongside the most iconic hominids (Neanderthals and Cro-Magnons). But mammals from before that time occasionally appear, usually — needless to say — the coolest-looking among them. It's not uncommon to see pre-Ice Age mammals erroneously depicted as living alongside the Pleistocene ones however.

Portrayals of prehistoric mammals have usually been more accurate than those of prehistoric reptiles since large extinct mammals have left more numerous remains and are easier to "bring to life" correctly in media, since we can just compare them with their modern relatives — though this doesn't entirely prevent inaccurate reconstructions. A good percentage of them received an increase in popularity just after the Turn of the Millennium, thanks to Walking with Beasts and a certain series of CGI cartoon movies, but others (especially the Ice Age ones) have been popular since long before then. They are nicknamed "megafauna" by some, but the term is not specific to mammals (nor extinct animals, for that matter), and there were plenty of prehistoric mammals similar in size to or smaller than their modern counterparts.

Stock Ice Age Mammals

NOTE: A few animals in this folder lived partially or totally before the Ice Age, but are here for comparison.

The Icon of the Ice Age: the Woolly Mammoth & the American Mastodon ***

Mammoths and mastodons often show up in anything dealing with prehistory: you can even see them living in tropical volcano-filled worlds alongside dinosaurs, but thankfully, mammoths are usually associated with the Ice Age. It's hard to imagine a prehistoric icy landscape without a curly-tusked mammoth wandering in.

The most commonly portrayed species of mammoth is by far Mammuthus primigenius (lit. "primeval mammoth"), better known as the woolly mammoth, or THE mammoth par excellence. It is probably the most iconic non-dino prehistoric animal of all, thanks to its resemblance to an elephant with huge curly tusks and dense hair, but also to the countless, extraordinarily well-preserved specimens with soft tissues found in northern Eurasia and northern Alaska and Canada. These findings have long made it one of the most accurately-portrayed of all prehistoric animals, and one of the very rare extinct animals almost as scientifically well-known as a still-living animal. However, the real cause of its extinction remains unclear, as is the precise meaning of the word "mammoth", which is of Russian origin. The most common theory is that it derives from a Native Siberian word for "earth", as frozen carcasses emerging from the permafrost were mistaken for huge burrowing beasts. "Mammoth" as an adjective derives from the extinct animal — the first person to use it that way was Thomas Jefferson (for a wheel of cheese, no less!), who had a major interest in paleontology.

Despite its familiarity, even this animal is not spared misconceptions and mistakes in its portrayals. The most common error is thinking the woolly mammoth was larger than modern elephants. Actually, the "woolly" was the same size as its tropical, 21st-century cousins — perhaps this is due to the confusion with other mammoth species that were a bit larger, like the Columbian, or Imperial, mammoth (Mammuthus columbi). Also note that only males had the typical huge, curled tusks; the females' tusks were not that different from those of modern elephants. As preserved fossil hair is often rich reddish-brown, some depictions show woollies with this color; actually, this is due to a chemical change in the hair during the intervening thousands of years. When alive, their hair could be black or dark brown, as seen in both Walking with Beasts and Prehistoric Park, or more rarely, pale "ginger" or even blond. The last notion comes from a genetic analysis made in 2006 on a sample. Woolly mammoths also had smaller ears and smaller tails to preserve heat, as well as humped shoulders and a dome of fat on their head that made their backs slope downwards.

It's worth noting that mammoths, scientifically speaking, were just another genus of elephant, since they belonged to the same family, Elephantidae. The Asian elephant (Elephas maximus) is slightly more closely related to mammoths (Mammuthus) than to its more distant modern African relatives (Loxodonta africana and Loxodonta cyclotis) — thus mammoths (and mastodons) weren't the direct ancestors of elephants as is sometimes claimed. Also within Elephantidae was Palaeoloxodon, the "straight-tusked elephant"; the best-known species of which is Palaeoloxodon antiquus of Mediterranean Europe and West Asia. Formerly believed to be related to Asian elephants, its now considered to be closer to African elephants. It also lived during the Ice Age, but it preferred warmer climates and was bigger than the woolly mammoth at about the same size as the Columbian mammoth. Other recently-extinct elephantids underwent a high degree of insular dwarfism, some becoming as small as an average sheep or pig.

On the other hand, the proper mastodons (whose common name curiously means "breast-tooth" for their blunt, cone-shaped teeth) were not true elephants, but just distant relatives of both mammoths and surviving elephants, and were much more primitive within the phylogenetic tree than Elephantidae (instead being in the family Mammutidae). The scientific name of the commonly-known species of mastodon, Mammut americanum (the American mastodon), is partially misleading: it was American indeed, but not a mammoth. The two are often confused with each other in pop-culture, but there are some key differences◊ — mastodons lacked the sloping backs of mammoths, were slightly shorter, had straighter tusks, and had differently shaped teeth adapted to eat leaves and branches instead of grass (the aforementioned "breast teeth"; mammoth teeth look like those of modern elephants). The last trait tells us mastodons were mainly forest animals, whereas mammoths preferred grasslands.

Like the woolly mammoth, the American mastodon has left exquisite remains (such as those in the Californian tarpits) — many complete skeletons, but no frozen specimens. It lived during the Ice Ages, but in warmer climates than Mammuthus primigenius, and was neighbor and possible prey of the sabertooth cat Smilodon fatalis. Interestingly, in some languages the adjective "mastodontic" or "mastodonic" has become a synonym of "huge" or "enormous", like the usage of "mammoth" as an adjective, although but the animal wasn't actually that big compared with other extinct proboscideans. Also worthy of note is that in the earliest days of palaeontology during the late 1700s, "mammoth" and "mastodon" interchangeably — which some people still do today. Other extinct elephant relatives are called "mastodons" or "mastodonts" in classic paleozoology, ex. Platybelodon, the "shovel-toothed mastodon", and Anancus, the "European mastodon", but they were not strictly related to the genus Mammut or even in the same taxonomic family.

1. Entry Time: N/A for the woolly mammoth, which has been a cultural icon since prehistory. 1864 for the American mastodon.
2. Trope Maker: Journey to the Center of the Earth (American mastodon)

Knife-Toothed Felines: Smilodon & Machairodus, aka the "Saber-Toothed Tigers" ***

Saber-toothed (or sabertooth) cats, with their distinctive fangs, are just as iconic in pop culture as the woolly mammoths, and the only other mammals worthy of three stars here. Mammoths and sabertooths (sabretooths in UK) have traditionally competed for the title of most iconic Ice Age mammal — just like Brontosaurus and Tyrannosaurus for title of most iconic dinosaur.

There were many species of saber- or sabre-toothed felines, but the ones you'll most likely see are the North American Smilodon fatalis ("fatal knife-tooth") and the South American Smilodon populator ("devastator knife-tooth"), which was larger but whose name sounds less cool when said out loud (even if its specific definition is awesome). The Old-World genus Machairodus ("sword-tooth"), often spelled "Macherodus" in old sources, has also been quite common, at least in non-fiction works, but lived slightly before the Ice Age, unlike Smilodon. Estimated at around a thousand pounds in maximum weight, S. populator was one of the largest cats to have ever lived, the same size as the extinct American lion and Eurasian cave lion, and was probably a descendant of S. fatalis, which was closer in size and weight to a bulky modern lion.

Although sabertooths belong to the cat family, Felidae, they are in a separate branch of that clade from modern felines, the hard-to-pronounce Machairodontines, or more simply the Machairodonts, named after Machairodus; thus, the name "saber-toothed tiger" (much more rarely, "saber-toothed lion") popularly applied to these creatures is not correct at all. The "tiger" thing has led to them being shown roaring with the same sound as an actual tiger or a lion, though only the big cats of the genus Panthera (that is, lions, tigers, jaguars and leopards) can produce such a roar, thanks to the structure of their larynxes, which is unique to this genus. Although the structure of the hyoid bones in sabertooths' throats were set up for roaring, it's uncertain if these roars were identical to those of modern big cats.

In media, Smilodons will also probably use their sabers for every conceivable task, most prominently slaying herbivores the size of mastodons or Megatherium with a single stab. However, most real sabertooths (as well as their relatives, the scimitar-tooths and dirk-tooths) had relatively delicate fangs that could not safely be used for stabbing. Instead, they probably used them to deliver a killing blow to the throats of their prey after disabling them. They would have preferred smaller prey too, such as juvenile mastodons and the smaller forms of ground sloth, as well as horses, deer, tapirs, bison, camels, giant armadillos, peccaries, and South America's unique native ungulates. They may be depicted as striped or spotted, just like a literal tiger or other big cats, which isn't completely impossible, but there isn't concrete proof of this: soft tissue of skin has not been preserved in the La Brea Tar Pits, where S. fatalis has been found in large numbers (over 2000 individuals).

Expect to see Smilodon, Machairodus, etc. frequently interacting with humans, as our ancestors' main predators; in Real Life, other carnivores such as the aforementioned prehistoric lions were probably more common predators of early humans. And expect to see them living in icy lands alongside woolly mammoths as well. Even though they were contemporaries, their habitats in Real Life were largely different, with Smilodon preferring warmer climates. However, S. fatalis would have experienced snowy winters, considering its region's climate at the time, and did live alongside mastodons and Columbian mammoths; S. populator lived in tropical grassland alongside elephant-relatives called gomphotheres, like Notiomastodon and Cuvieronius. Neither species of Smilodon lived at the far northern latitudes where woolly mammoths were found, though another saber-toothed cat, Homotherium, did. And, in less serious works, don't rule out seeing saber-toothed cats somehow living alongside dinosaurs, and in the most extreme scenarios, fighting against a T. rex.

In Real Life, Smilodon was an animal exclusive to the Americas (the New World), filling the niche the other sabertooths, Machairodus for example, were occupying in the Old World (Europe, Asia, Africa). Smilodon was among the most specialized members of the Carnivoran order of mammals. Its hindlegs were shorter than its forelegs, like hyenas and some bears, and it had a stubby tail; it was powerful but quite slow-moving, and agile only in a straight line: in other words, a sort of Mighty Glacier. The lower jaws were more gracile than modern big cats', and had a loose hinge that allowed them to open incredibly wide convergently with hippos, but were not apt for delivering powerful crushing bites, similar to snakes' jaws (venomous snakes often have upper fangs surprisingly similar to a sabertooth's). Smilodon had the biggest/longest fangs among all saber-toothed cats; this, together with its body size, might explain why it's become the most famous member of the group (and often cited as THE sabertooth par excellence). Only the earlier, distantly-related pseudo-cat Eusmilus had fangs of comparable size.

The "sabers" of Smilodon were arguably used only for slashing the throats of prey that had already been subdued with its bodybuilder-like forearms; the molars and lower canines were smaller than those of modern cats but the incisors were bigger, and more apt than the canines for tearing off flesh from its prey's body. Smilodon is often portrayed living in wolf- or lion-like groups with both sexes actively hunting, though this is considered controversial by some scientists as there is not enough actual evidence to support it. Some artists have even depicted smilodonts with a totally speculative lion mane, linking it with the social behavior that is practiced by lions but unusual for other modern felines. The modern feline with the longest fangs today in respect to the body is the smallish clouded leopard of Asia (Neofelis); the one with the bulkiest body-frame is the larger jaguar (Panthera onca) of the Americas. The overall biggest modern feline is Panthera tigris altaica, the Siberian Tiger, with some individuals getting as big as extinct cave lions or American lions.

Smilodon went extinct roughly 10,000 years ago, around the time the Ice Age ended. Like the mammoths, theories have been raised as to how they died off, such as climate change at the end of the Ice Age, the lack of big prey for them to hunt, or humans changing their habitat by setting fires and killing off their food supply. Anyway, it's certain that they didn't evolve into modern cats, because as mentioned above, they were from a distinct cat lineage from modern felines.

1. Entry Time: 1903 (Smilodon fatalis); 2001 (Smilodon populator)
2. Trope Maker: The paintings of Charles R. Knight (Smilodon fatalis); Walking with Beasts (Smilodon populator)

Big Upright Beasts: Megatherium & the Ground Sloths **

One of the largest and most spectacular land mammals that ever lived, Megatherium americanum was the same size as an elephant or a T. rex: it reached 5m tall when standing fully erect, like a giraffe but much heavier. Indeed, the name "Megatherium" means... well... "big beast".

This is probably the most famous extinct mammal that doesn't really look like an ancient version of its still-living cousins, and is probably also the most famous one whose name ends in -therium. While mammoths and mastodons could be regarded as the "brontosaurs" of their time and sabertooths the "tyrannosaurs", the megathere (but also the woolly rhinos and glyptodonts below, and to some extent, also the cave bear) can be considered the "Ice Age Triceratopses and/or Stegosauruses": that is, the Giant Herbivorous Tanks of their time.

In old reconstructions, Megatherium was shown with a horse-like head and sometimes a giraffe-like tongue to reach foliage on the tree tops. The horse head and giraffe tongue are probably mere fantasies, but the high-browsing habits aren't; indeed, the robustness of its body allowed it to stand on only its hind feet — which, curiously, had only one claw each, and were not flat on the ground but facing to each other like an orangutan's feet — and on its robust tail like a tripod, while the three-clawed, bear-like forefeet were used to pull down branches, like what is thought about the large, convergently-shaped therizinosaur dinosaurs. When quadruped, Megatherium probably knuckle-walked with its forelimbs like a modern giant anteater, as its claws were too big to be placed flat on the ground.

Actually, our "big beast" was neither a horse nor a giraffe relative, nor was it a giant bear... it was a sloth. More precisely, the stock animal within the group called ground sloths, which are not only related to modern sloths, but also to anteaters and armadillos, and not to ungulates or carnivorans. The most famous pictures of Megatherium show it with fur, like a modern sloth, and to some extent this has been validated by fossilized hair imprints from other ground sloth species. However, there is also speculation that due to its sheer size, Megatherium was hairless, much like an elephant or rhinoceros. It probably gave birth to one offspring per time and carried the babies on its back, like modern sloths and anteaters do, but the length of its gestation can only be guessed.

An extremely controversial idea is that ground sloths might have supplemented their diet with meat that they scavenged from predators such as sabertooths by chasing them away from their kill. There isn't much to support this theory other than Rule of Cool, though. It is entirely possible that they ate a little meat every now and then, since modern herbivores like deer do the same thing for a protein supplement. However, this would not be a standard part of their diet, and they would more likely prefer plants. This didn't stop Walking with Beasts from depicting Megatherium chasing some Smilodons away from their kill and eating it, and since then, it has been forever cemented as an omnivore in video games such as Zoo Tycoon and ARK: Survival Evolved. In the former game, it will eat any meat placed in its enclosure, but otherwise does not kill and eat other animals sharing its habitat; the latter goes for a more realistic interpretation by depicting it as an insectivore, like anteaters and armadillos, hunting giant insects and arachnids. Some portrayals take this idea up to eleven by having it be an active hunter, knocking over animals like the tank-like glyptodonts to tear open their soft bellies with its claws, almost like a mammalian Tyrannosaurus rex.

Megatherium is the most well-known species of ground sloth, due to being the largest, hence its popular name, the giant ground sloth. The only similarly sized ground sloth alive at the same time was the Central American Eremotherium laurillardi, the Panamerican ground sloth. Like Smilodon, it's commonly depicted alongside mammoths, despite being strictly South American (mammoths never reached this continent). The proboscideans that did reach South America, such as Cuvieronius and Notiomastodon, are classified as gomphotheres, a primitive family more closely related to elephants and mammoths than mastodons were. Different sloth species that reached North America, such as Nothrotheriops and Megalonyx, would've been the ones contemporary with mammoths and the American mastodon.

Megalonyx jeffersoni, or Jefferson's ground sloth, was the ground sloth species most common in Ice Age North America, but it was about half the size of its more famous cousin. It was first described in 1797, believe it or not, by Thomas Jefferson! Naming it based only on some claw bones, he tentatively classified it as being a huge lion (it was properly identified as a sloth in 1799, though the not-yet President did acknowledge similarities to the then-new Megatherium in his original description). Since the existence of prehistoric life was still controversial at the time, he believed Megalonyx, as well as mammoths and mastodons, could have still been existing in the American wilds — he even asked Lewis and Clark to find him live specimens on their expedition! Two other similarly-sized North American Ice Age grounds sloths are Paramylodon harlani (Harlan's ground sloth) and Nothrotheriops shastensis (the Shasta ground sloth); contrasting with the forest-dwelling Megalonyx, the former was a grasslands animal commonly found in the La Brea Tar Pits, while the latter preferred deserts. Among the "small" ground sloths of South America, the most notable is Mylodon darwini, the first fossils of which were Mylodon were found by Charles Darwin during his voyage on HMS Beagle, earning it the common name of Darwin's ground sloth. The Caribbean also supported many dwarf ground sloths that survived until 5000 years ago when humans colonized the islands, long after their huge mainland kin went extinct.

The most famous ground sloth in fiction is Sid from the Ice Age franchise, who is only about the size of a human, and resembles no ground sloth in real life, much less Megatherium. He looks more like a modern tree sloth, which the animators did indeed model him off of, but with bizarre protruding eyes. In prehistoric terms, he seems to be closest to the Shasta ground sloth at least in terms of appearance. The most improbable portrayal of these critters would have to be in the 1948 B-Movie Unknown Island, where a ground sloth was depicted as a strange, roaring predator resembling a cross between a gorilla and a bear.

1. Entry Time: 1854
2. Trope Maker: Crystal Palace Park

Hairy Nordic Rhinos: the Woolly Rhinoceros & Elasmotherium **

Mammoths weren't the only "woolly" creatures that lived in the Ice Age. Special mention should be given to the slightly less famous but still notable woolly rhinos, the "ceratopsids" of their time, and possibly subject to Rhino Rampage.

Elasmotherium sibiricum ("Siberian thin-plate beast"), also known as the Siberian unicorn, is probably the biggest true rhinoceros known: it's often confused with the proper woolly rhino (Coelodonta antiquitatis, "hollow tooth of antiquity") because of their similar appearance. However, the woolly rhino was no larger than modern white rhinos and had two horns as well; it was closely related to the modern Sumatran Rhinoceros, the smallest extant rhino species (and the only one with some hair on its body). Elasmotherium, on the other hand, was much larger (5 tons, like a modern bush elephant) and with a single horn... on its forehead rather than its nose; hence the "unicorn" label. Unlike the "woolly", the Siberian unicorn was not closely related to any of the five modern rhinoceros species, though it still belonged to the rhino family, Rhinocerotidae.

Both rhinos lived in the Ice Age in cold climates alongside the other, more popular woolly (guess what). But whereas the elasmothere was restricted to Eastern Europe and Central Asia, Coelodonta ranged as far as Spain (there is, however, a cave painting that might stretch Elasmotherium's range as far as France). Like the elephantine "woolly", the rhinocerotine one (we're always talking about Coelodonta) has left behind soft parts of its body, hair and horns included, in the form of frozen corpses. We also know from cave art that it had brown fur, with a darker band in the middle of its body.

It's important to note that rhino's horns are not made of bone like the horns of cattle and deer, but of hardened hair, and don't usually preserve as fossils. The anterior curved horn of the proper woolly rhinoceros was laterally flattened, and some have speculated it used it to free the terrain from snow to reach the vegetation below, like modern caribous do with their hooves and antlers (and like woolly mammoths may have done with their tusks). The coelodont also had a hump on its shoulders like a bison. Its teeth tell us it was a grazer like white rhinos

Unlike the woolly rhino, we don't know what size and shape the elasmothere's horn actually was, because it has never found. Traditionally, it's been believed that it was enormous, as long as a man is tall and possibly the longest horn in the animal kingdom. More recently though, it's been suggested that the elasmothere's horn was actually short and blunt, something along the lines of the modern-day Javan rhinoceros — in which case Elasmotherium might not quite have been the "prehistoric unicorn" it is often imagined to be. Both the woolly rhino and Siberian unicorn had three toes for each foot like the modern ones, and probably reproduced in the same manner, giving birth to one (hornless) calf after a very long gestation, like modern rhinoceroses but unlike hippopotamuses, whose pregnancy is rather short for their size (8 months vs. a rhino's 18). Both rhinoceroses went extinct without leaving descendants. Like with many of the Ice Age megafauna, it appears the combined pressures of human hunting and climate change did these creatures in.

The elasmothere is often thought to have been the inspiration for the Unicorn myths found all over Eurasia in one form or another when still alive, but this is mere speculation. There's a chance it might have lived into historic times, but the anecdotes and depictions of these creatures might just as well refer to Indian rhinos, one-horned bulls, or animals frozen in the permafrost like mammoths are known to have been.

1. Entry Time: 1918 (Coelodonta), 2006 (Elasmotherium)
2. Trope Maker: The Land That Time Forgot (Coelodonta), Prehistoric Park (Elasmotherium)

Giant True Bears: the Cave Bear & the Short-Faced Bear **

Among the prehistoric mammals of the order Carnivora, the most famous after the saber-toothed cats are the giant bears, again from the Pleistocene Ice Age.

The most well-known is the cave bear (Ursus spelaeus, meaning "cave bear" in Latin), so-called because its remains are extremely abundant in European caves, more than those of other "cave mammals" (see below). These "cave" beasts are probably at the origin of the subtrope to putting "cave" before the name of fictional extinct animals, falling under Whatever Saurus.

Quite similar to a modern Kodiak bear in shape and size, but with a bigger hump on its shoulder and a more prominent skull, the cave bear was perhaps the closest relative of brown bears (Ursus arctos), and usually depicted with the same brownish color of the latter, as cave paintings suggest. It was also related to the polar bear, an animal that recently evolved from brown bears living by the icy seas of the North Pole, together with the Great Auk, a penguin-like bird recently extinct in 1800. In 2020, the first frozen mummy of a cave bear was been found in Siberia.

The cave bear was probably a mainly peaceful creature that cared its tiny offspring in its warm rocky homes; but it had also classically been described as the archenemy of Neanderthals and Cro-Magnon humans, because both humans and bears lived in the same places (Pleistocene Europe) and were forced to share the same caves to protect themselves from the frigid Ice Age winters. But it's more probable that Neanderthals and Cro-Magnons were actually the worst enemies of cave bears, and some think they could even have contributed to the bear's extinction. Studies show the cave bear to have been to an almost pure herbivore, like the living giant panda, living on a strict diet of berries and shrubs (though, like pandas, it may have supplemented its diet with meat every now and then). In fact, the inflexibility of its diet may also have contributed to its extinction.

The North American short-faced bear (Arctodus simus, lit. "short-muzzled bear-tooth"), in contrast to its stockier cousin, had long limbs, a bulldog-like snout, and a more carnivorous diet. At first glance, it seems like it would be an agile and fast runner, and a very powerful hunter. However, more recent studies show that its limbs were too gracile to wrestle large prey to the ground, and too fragile for sharp turns, the latter of which are required for a fast-running hunter. Thus, these studies proposed it was purely carnivorous like a polar bear and a scavenging "kleptoparasite" that stole prey from other predators by scaring them away with its large size. However, very few animals can live entirely on scavenging (vultures are an exception, as they can fly for miles without eating), and additional studies have hinted that it may have been a generalist omnivore like other bear species. Bears in general can be qualified as Lightning Bruiser, like rhinos/hippos, as they are massive but fast runners compared with the probably slower giant sloths and glyptodonts.

Expect these two bears to be confused in pop culture despite being quite different in appearance, and the short-faced bear being more related to the South American spectacled bear (Tremarctos ornatus) than the modern grizzly or the cave bear. Also expect both to be depicted as hunters of large prey, despite the above noted actual diets. Another thing to note is that despite most books describing the short-faced bear as the largest bear, that title actually belongs to its South American relative Arctotherium ("bear beast") — not unlike how the South American Smilodon populator was bigger than the North American Smilodon fatalis.

1. Entry Time: 1897 (cave bear); 2000s (short-faced bear)
2. Trope Maker: A Story of the Stone Age (cave bear); recent documentary media (short-faced bear)

Living-Tank Mammals: Glyptodon & Doedicurus **

After ankylosaurs went extinct, evolution decided to create their perfect mammalian equivalents: the glyptodonts. Like the ground sloths, they were xenarthrans (formerly called edentates), the group containing sloths, anteaters, and armadillos, the last of whom they were related to. Despite the old name "edentate" means "no teeth", both ground sloths and glyptodonts had strong molar-like teeth, but small or no frontal teeth.

Glyptodonts lived in South America for millions of years before going extinct only a few thousand years ago: in other words, they had the same history as their cousins, the ground sloths. Both groups were herbivores, and glyptodonts fortunately have never been depicted as meat-eaters or predators in popular media unlike their relatives. Rather, they have often been compared with giant tortoises because of their shell-like armor and short "hoofed" feet. Like the ground sloths, as adults they feared no predators (not even the saber-toothed cats), except of course humans. The size of the largest glyptodonts tends to be sometimes exaggerated in docu-media; they were actually much smaller than Megatherium, being not taller than an adult man — but their mass was nonetheless as much as a small car, and thanks to their heavy armor, they weighed two tons, like a modern rhino or hippo (which is still smaller than the elephant-sized Ankylosaurus).

There is a secret behind ground sloths' and glyptodonts' success: their backbone. It was far, far stronger than that of any other mammal, thanks to special protrusions (the xenarthral bones, hence the name "xenarthrans") in their vertebrae that permitted them to carry such heavy bodies around without suffering back pain. Some think glyptodonts were even able to briefly rear up on their pillar-like hindlegs, which had enormous femurs and an insanely robust pelvis (like those seen in the ground sloths), making them analogous to stegosaurs. But unlike stegosaurs, glyptodontids were live-bearers, and like modern armadillos, their young were born from their mothers already with their armor formed.

Glyptodon clavipes ("club-footed sculpted tooth") is the archetypal and most well-known glyptodont, whom the group is named after; it had a round upper shell like a tortoise, coupled with a small round head (perhaps ending in a small "trunk" as show in some illustrations; cave paintings from South America challenge this idea) and a short, stocky tail covered in small but pointy spikes. The modern animal that perhaps resembles Glyptodon the most is the 30 kg giant armadillo, Priodontes maximus, of the Amazon Basin. Ironically, the closest living relative of the glyptodonts is the pink fairy armadillo (Chlamyphorus truncatus), the smallest armadillo species!

But it's also worth mentioning the even more armored Doedicurus clavicaudatus (lit. "club-tailed pestle tail": this is the biggest/longest known glyptodont, and the one seen in Walking with Beasts, Zoo Tycoon 2, and ARK: Survival Evolved). It was very similar to Glyptodon, but with its long flexible tail covered in massive spikes at the end, it was the most stegosaur- or ankylosaur-like of all glyptodonts, easily able to kill even a smilodont with a single blow from its "medieval mace". The Doedicurus' spiky tail would have been even more dangerous for enemies than the Ankylosaurus' more rounded one — recalling more a stocky Stegosaurus "thagomizer". Injuries inflicted by Doedicurus on others of their kind suggest they used their club-tails in intraspecific combat, likely for mates or territory. Doedicurus amd Glyptodon are the most-often depicted of the group, also because they were among the biggest and most powerfully armed.

Glyptodont dorsal armor was the strongest among any land vertebrate, tortoises excluded. It was made of a single piece consisting of several scutes fused together, smooth and usually round, unlike ankylosaurs and armadillos whose armor was more flexible (and spiky in the case of ankylosaurs). With their compact frame, pillar-like legs, and rigid armor, glyptodonts were probably slower-moving than ankylosaurs and armadillos, but still faster than a Galapagos tortoise. Despite these differences, glyptodont armor was astonishingly similar to an ankylosaur's — only the upper parts of the body were covered; the underbelly was unarmored (but hairy like in modern armadillos); the head had a "shield"; and their tail was covered by bone. We don't know if ground sloths and glyptodonts were solitary or lived in herds: modern xenarthrans are usually solitary, but the nine-banded armadillo has the singularity to give birth to four twins all the same gender.

Like Megatherium, Glyptodon and Doedicurus were known to ancient humans; if seen from far distances, it could have given to us the curious impression of a big walking ball roaming slowly across the grasslands. Despite appearances, glyptodonts were totally unable to roll into an actual impenetrable ball like what some South American armadillos, or also the unrelated pangolins and hedgehogs of the Old World, do. They weren't also able to retreat their heads, limbs and tails in a tortoise-like manner; their size, armor, and body robustness were alone effective defense, like in marine turtles.

We now know human hunting wiped out the ground sloths and the glyptodonts, as the species on islands were the last to go and there is evidence of human hunting and change in their habitat. Ancient humans often used the biggest glyptodonts' shells as body armor for themselves or even as makeshift huts. Now, only far smaller xenarthrans survive; armadillos (which were not glyptodont descendants but only relatives), tree sloths (again, relatives and not descendants), and anteaters (sadly, the natural history of anteaters is poorly understood), all Central/South American, except for the nine-banded armadillo, which has colonized part of the USA. Incidentally, there is one species of glyptodont known from Ice Age North America, that being the large Glyptotherium, found in Southern USA and Mexico.

1. Entry Time: 1864
2. Trope Maker: Journey to the Center of the Earth

Up To Eleven Trophy: Megaloceros **

Now we return in the world of the hoofed mammals (remember that rhinos are true ungulates, but mammoths & elephants are not), this time with an artiodactyl, aka an even-toed hoofed mammal.

The most spectacular extinct deer, this is one of the most depicted extinct mammals in prehistory books because of its antlers, but is rather uncommon in Fictionland. Megaloceros giganteus simply means gigantic "big horn": continuing the Running Gag of comparing Ice Age mammals with dinosaurs, Megaloceros could be considered the "hadrosaur" of its time, for its huge size but slender running frame, spectacular head ornamentation like that of the Parasaurolophus, and its ecological niche as prey for other mammals (humans included), just like "duckbills" in the Cretaceous.

But wait: even though it is commonly referred to as the Irish elk^note In British English, elk = moose., Megaloceros (also called "Megaceros" in older sources, with the same meaning of "big horn") was more closely related to the European fallow deer — indeed, in many sources, it is more generically named the "giant deer" (though Finnish author and paleontologist Kurten Bjorn gave it the name of "shelk" in his prehistoric novel Dance Of The Tiger). It wasn't the largest deer ever — though it was as large as a moose, even bigger deer lived elsewhere in the Ice Age — but its antlers were another matter: they would make a modern moose's antlers look puny. Each one was as long as the entire animal's body (each as long as an adult person is tall, as stated in Walking with Beasts), and each weighed more than 100kg — more than any other known deer species. They are probably the biggest known "horns" (sensu lato) of any mammal, and rivalled even the biggest horns and spikes of the ceratopsid dinosaurs; but it's possible that the unknown single horn of the giant rhino Elasmotherium was the same size, or even bigger, of the megaloceros' antlers.

As with all modern deer (except for reindeer and caribou), only males had such headgear, which in reality, more resemble a moose's flat antlers than the typical deer's branched ones. Some scientists believe that the antlers alone were the cause of its extinction, having grown too big. This phenomenon is called "hyperthely": classically-cited examples of modern hyperthelies are the peacock's tail, the toucan's bill, the right pincer of the fiddler crab, and the narwhal's spiral tooth. This hyperthely should have made the giant deer too clumsy, but this is unlikely. Megaloceros males were stronger than females but probably just as agile, as with extant deer species: besides, if their antlers actually were too big, evolution probably would have just made them smaller at some point. More likely, climate change, combined with hunting pressures, lead to its extinction.

Megaloceros lived in Europe and Asia alongside woolly mammoths and other large mammals, and was possibly prey for ancient humans (Walking With Beasts show Cro-Magnons successfully killing one adult male Megaloceros that was tired after fighting another male); its nickname "Irish elk" is due to its remains being very common in Ireland. Its huge antlers are often found isolated in this country (all true deer loose and regrow their antlers seasonally), and have even been used as a tool to cross small streams! In The Lost World (1912), the explorers briefly glimpse some kind of giant deer, and protagonist Edward Malone — an Irishman — suggests that it was probably one of "those monstrous Irish elk which are still dug up from time to time in the bogs of my native land." Cave art also tells us it had a hump on its shoulders with a white head and a brown body, as depicted in Walking With Beasts.

Other large, spectacularly antlered extinct deer include Eucladoceros ("well-ramified horn") and Cervalces ("deer-moose"), the former nicknamed the Bush-antlered Deer, the latter nicknamed the Stag-Moose. The biggest Cervalces species had a smaller set of antlers, but had a larger body than the Irish Elk; Eucladoceros was smaller-bodied but had an incredibly high number of points in its antlers. The former lived alongside Megaloceros during the Pleistocene Ice Age, but the latter lived in the Pliocene epoch before the Ice Age. Other prehistoric deer had more normal-sized headgear.

1. Entry Time: 1854
2. Trope Maker: Crystal Palace Park in London (believed to be the most realistic animal model of the park)

Big Badass Wolf: the Dire Wolf *

The dire wolf (Aenocyon dirus, formerly Canis dirus) was a recently extinct canid (the dog family) exclusive to the Americas, famous for being bigger/stronger than our wolves, and possibly a hunter of giant bison in competition with saber-toothed cats and extinct American lions. It has been often found in the La Brea Tar Pits, with over 4000 individuals known along with many other Pleistocene American mammals both living and extinct. This animal could be considered the mammalian "raptor" of the Ice Ages.

Despite its fame of power and direness, the dire wolf wasn't much larger than the modern grey wolf (Canis lupus). However, it had a much more powerful bite, well over twice that of the grey wolf, and thus often compared to that of a hyena. This would allow it to be a fair competition to other predators at the time. It ranged from as far north as Canada to as far south as South America (though only in the northern and western areas, due to the obstacle presented by the Andes). Like the bears above, neither of which left descendants in modern world, the dire wolf is not the ancestor of modern wolves. It was originally believed to be closely related to the grey wolf, but DNA studies reveal it to be of a uniquely North American lineage of canids most closely related to the African jackals (Lupulella). So while it is popularly depicted as looking like a modern wolf, right down to the fur color, the dire wolf might have looked very different when alive. And while we do know it was a pack hunter, it may have had a different hunting style and may not have had its packs dominated by an "alpha" pair like in modern wolves. However, it likely gave birth to several puppies that were raised with love, like what present-day pack-hunting wild dogs.

Surprisingly, this canid is less common in works set in prehistoric times, and more common in fantasy works such as Dungeons & Dragons and, most famously, A Song of Ice and Fire and its television adaptation Game of Thrones. When it appears, expect it to be double the size of a real grey wolf, despite not being much larger in real life. Expect it also to be described in books as "the biggest canid ever", though some Borophagines, nicknamed "bone-crushing dogs", that lived well before it were actually larger (the record belongs to the Miocene North American borophagine Epicyon).

1. Entry Time: 1977
2. Trope Maker: Dungeons & Dragons (1st Edition Monster Manual)

Bigfoot or King Kong?: Gigantopithecus *

This extinct primate is surely the most popular today in media (human ancestors excluded, of course), one reason being its size. Other giant primates of the past include huge baboons like Dinopithecus and the giant lemurs of ancient Madagascar.

Originally thought to be an enormous prehistoric human, later research made it clear that Gigantopithecus blacki was a relative of the orangutan that had also convergently exhibited gorilla-like characteristics. Found in Southern Asia from China to India, its name means "giant ape", and with good reason. It's estimated to have measured up to 10ft/3m when standing upright, twice as tall as a modern silverback gorilla; sort of midway between a Real Life gorilla and King Kong. If it lived alongside dinosaurs, it could have made for a realistic Primate Versus Reptile.

Sadly, the only parts of it known from the fossil record are the jaws and teeth, with the rest of the body having yet to be uncovered; the shape of the teeth show us it was a plant-eater, possibly specialized to a bamboo-based diet just like a gorilla, to the point that some experts think competition with the giant panda actually drove it to extinction. Gigantopithecus lived alongside the Asiatic Homo erectus before going extinct, but we don't known how they interacted with each other due to the scarcity of remains of either.

At least part of the reason this ape has entered stock territory is due to some scientists speculating that it might have been the inspiration for the mythical yeti (especially since it was also discovered in the Himalayas). Some cryptozoologists have taken these theories even further, speculating that not only did it survive to modern times, but at least one lineage migrated to North America and evolved into Bigfoot. Thanks to this radical theory, Gigantopithecus has been mentioned in virtually every Bigfoot documentary.

There are quite a few problems with this theory. First of all, there is absolutely zero fossil evidence that it survived that long, much less that it made it to North America. It's quite unlikely that such a large creature could go unnoticed for so long without leaving some sort of proof of its existence. Secondly, since the creature was specialized for eating mostly bamboo, it's doubtful it would survive in a temperate environment without its preferred diet,^note While there are native bamboo species in North America, they're confined to what's now the Southeastern United States and Mexico, meaning Gigantopithecus would've needed to migrate across a vast distance without any of its preferred food, and those American bamboos might not even have been close enough to be edible to it (giant pandas tend to be rather picky about which bamboos they eat, and it might've been the same for Gigantopithecus ). much less spread throughout North America.

Despite this, the "Gigantopithecus = Bigfoot" theory is so popular that the ape is often depicted in models and illustrations in an upright stance like a man, just to fit with this idea. Since all we have are its jaws and teeth, it's hard to be sure, but judging by its relationship with other apes, it most likely walked on its knuckles like most great apes do today. Since primates that habitually stand and walk upright require a specialized foot structure extremely different from that of other apes, Gigantopithecus evolving a similar foot structure to that of humans would be a radical case of convergent evolution. Also, if it was as large as believed, its immense weight would cause great stress on its ankles and would be better-distributed by walking on all fours.

In The New '10s, Gigantopithecus made two notable film appearances. First, there was the villainous pirate Captain Gutt in Ice Age: Continental Drift. Then in The Jungle Book, a 2016 remake of the 1967 Disney classic, King Louie was changed from an orangutan to a surviving Gigantopithecus, averting Misplaced Wildlife in favour of Anachronism Stew (orangutans live in Southeast Asia, not in India where the story is set, but Gigantopithecus has been extinct for about 350,000 years). The latter appearance could very well place this creature in the public's mind for quite a long time, since not only was he quite humorous, being voiced by Christopher Walken and all, but he was much more menacing than his 1967 counterpart, chasing Mowgli through the ancient temple ruins in a memorably chilling sequence. That said, both film appearances correctly depict Gigantopithecus as an orangutan-like ape, walking quadrupedally on its knuckles as opposed to upright like a human.

1. Entry Time: The New '10s
2. Trope Maker: Yeti and Bigfoot documentaries, and the two aforementioned films

South American Tapir-Camel: Macrauchenia *

Macrauchenia patachonica was a famously enigmatic creature that lived in South America during the Ice Age (although earlier species in the same genus date as far back as the Miocene); its name means "big llama of Patagonia". It did indeed resemble a llama or humpless camel in appearance, but actually belonged to a now-extinct group of uniquely South American ungulates called the litopterns; once thought to have no modern relatives, newer research shows they are a sister group to the perissodactyls, the odd-toed ungulates.

The size of a horse, one of its most distinct features is its nostrils, which on the skull were located on its forehead like a whale's blowhole. Early depictions showed it as swamp-dweller that used its weirdly-placed nostrils to breathe while eating water plants (Aquatic Sauropods, anyone?), but we now know it to be a fully terrestrial animal that ate both leaves and grasses. This lead to it always being depicted with a flexible tapir-like proboscis, which would be helpful for pulling down branches to get at greens. However, if you compare a tapir skull◊ to that of Macrauchenia◊, you can see that the tapir has a bony projection on its forehead to hold the proboscis in place, which Macrauchenia lacks. Therefore, it's more likely the animal had a bulbous trunk similar to that of a Saiga antelope, instead used to filter dust on the plains of Pleistocene South America. Others however think it might have lacked a trunk completely and instead sported a plain moose-like snout with fleshy lips for grabbing at plants (cave paintings from South America depicting long-necked animals with trunks◊ challenge this idea though).

Another distinctive feature of the Macrauchenia is its long legs and rhino-like feet, which were not only built for extremely high speeds, but also some of the sharpest turns for any herbivorous mammal. This makes sense when you realize it evolved alongside the famous terror birds, which were not only fast runners but, like most birds, had very good color vision, meaning camouflage was useless. Other predators of included carnivorous marsupial-relatives like Thylacosmilus and terrestrial crocodile-relatives like Barinasuchus. After the formation of the Isthmus of Panama led to the Great American Interchange (remember, South America was an island not unlike Australia for most of the Cenozoic), North American "invaders" like cougars, jaguars, the giant bear Arctotherium, the wild dog Protocyon, and, most famously, the sabertooth Smilodon populator became the new top predators. Macrauchenia patachonica thrived in spite of the new dangers and became one of the last surviving litopterns, only going extinct after humans entered South America about 10 thousand years ago. It's likely that the first South Americans hunted these unusual animals to extinction, ending their unique lineage forever.

The sheer oddness of Macrauchenia's appearance has earned it many appearances in documentary and non-documentary media, including Walking with Beasts, the Ice Age franchise, and even an episode of Futurama. However, it's usually relegated to the role of an unnamed background animal, and despite the ongoing debate surrounding what was going on with its nose, most go for the tapir-trunk, most likely due to Rule of Cool.

1. Entry Time: 2001
2. Trope Maker: Walking with Beasts

South American Hippo-Bull: Toxodon *

Though less often portrayed than Macrauchenia, Toxodon also make occasional appearances in media, e.g. Prehistoric Park, in which it is shown as the main herbivore of the time and as Smilodon populator's main prey, much like how Macrauchenia was in Walkingwith Beasts.

Toxodon platensis ("flattened bow tooth") was bigger than the "tapir-camel", being 1.5 metric tons weight (about a thousand lbs heavier than Macrauchenia), and was probably the most common plant-eating mammal Ice Age South America (although like Macrauchenia, earlier species existed since the Miocene). Toxodon belonged to an extinct order of natively-evolved South American hoofed mammals called the notoungulates, lit. "the southern ungulates", and was one of the biggest and latest-surviving members of the group; they were a sister group of the litopterns and like them, most closely related to the still-living perissodactyls. Both Toxodon and Macrauchenia were discovered by Charles Darwin during his famous voyage on the HMS Beagle; the sheer strangeness of both animals stumped Darwin, playing a major role in his formulation of the theory of evolution.

Toxodon's look may recall for some that of a stockily-built, hornless buffalo, but it had a wider mouth and strong incisors like a horse. Its body and limbs were stockier than cattle, its head was held low to the ground, and the feet had four or five digits with small "hooflets"; thus, it has been classically compared with a hornless rhino or a small-headed hippo. Toxodon was once thought to have been a slow-moving, semi-aquatic animal — today, we believe it was fully terrestrial and capable of running rather quickly, as seen in Prehistoric Park, where one is shown even keeping pace with Nigel Marven's vehicle. The toxodont was arguably not as fast as the Macrauchenia, but thanks to its massive frame, it was a harder target for predators to kill than the relatively more slender Macrauchenia. Terror birds probably were unable to kill a fully grown toxodont, while other predators, like the mighty Smilodon populator, could have been able to do so, but not easily.

Both Toxodon and Macrauchenia thrived in Pleistocene South America, and it's easy to imagine vast herds of them roaming the pampas like the zebras and buffaloes of Africa today. Like their neighbors, the ground sloths and glyptodonts, these endemic South American ungulates lived around to meet the first humans to enter South America, and were likely driven to extinction by them. The last Toxodons vanished roughly ten thousand years ago, likely depriving the Smilodons of South America of what might have been one of their main prey sources and definitely spelling the end for Darwin's strangest animals.

1. Entry Time: 1912
2. Trope Maker: The Lost World (1912)

Prehistoric Buffalo: Bison priscus & Bison latifrons *

Among the megafaunal mammals that roamed the North American Pleistocenic landscapes (in a time when humans still lived only in Africa and Eurasia), besides the more famous mammoths, mastodons, sabertooths, ground sloths, and dire wolves, there were also several species of true bison (belonging to the scientific genus Bison).

The most famous, but not the biggest, is probably the steppe bison, Bison priscus (the one live-acted in the last episode of Walking with Beasts), closely related to the two modern species (Bison bison, the familiar American bison, and Bison bonasus, the rarer European bison or wisent). It was, however, a bit bigger than both, similar in size to the largest modern wild bovine, the so-called "Indian bison" or gaur (Bos gaurus, more closely related to domestic cattle). The Steppe bison had, more strikingly, longer horns than its two living kin — more like those of an African Cape buffalo or an Indian water buffalo. It ranged across the icy plains of the northern hemisphere, from Europe to Canada, and likely originated in eastern Eurasia.

An especially famous specimen of Bison priscus was found mummified in Alaska in 1979; nicknamed "Blue Babe" because of the color it acquired during its preservation, its frozen meat was still edible (its discoverers actually ate a chunk of it!) and its corpse shows perhaps signs of attack from Ice Age American lions (Panthera atrox). The carcass is wonderfully preserved, even more than many woolly mammoth specimens, resembling almost a living bison, and the animal appears lying on its knees like a "sitting" bison.

The long-horned bison, Bison latifrons, is today the biggest known wild bovid to have ever lived, and its name means "wide-front bison". Unlike the wider-ranging steppe bison it lived only in Pleistocene North America, but its horn-span reached 7ft/2m in width, more than a standing human, but still less than the horn-span of Megaloceros giganteus. It was arguably a more difficult meal for predators than Bison priscus.

Neither of these were the ancestors of the two species of modern bison. The American bison seems to be descended from a second, smaller species of Ice Age North American bison, B. antiquus, or the ancient bison; the European bison's origins are a little more mysterious, but fossils and cave art indicate it was already existing alongside the steppe bison.

1. Entry Time: Undetermined
2. Trope Maker: Documentary media

Lofty Critters: Camelops and Aepycamelus *

When we think North American wildlife, we tend to think stuff like bears, bison, deer, wolves, and cougars. So it comes as a surprise to many to learn that camels (and their South American relatives, the llamas and alpacas; together, they form the family Camelidae) were once considered characteristic of North American fauna. Indeed, camels and llamas evolved in North America and were only found on that continent until relatively recently when the ancestors of today's dromedaries and Bactrians (both in the genus Camelus) crossed over Beringia into Asia and the ancestors of llamas and alpacas (genus Lama) entered South America across the newborn Isthmus of Panama.

Even despite the migrations, camels remains abundant in North America all the way until the very end of the Ice Age. The most prominent of these is Camelops hesternus ("camel face of yesterday"), a fairly modern-looking camel about the same size as a Bactrian camel. Also known as the western camel or yesterday's camel, Camelops was a grazer like the Bactrian camel, and ranged from Alaska to Mexico. Its fossils are quite common in the La Brea Tar Pits, but no preserved soft tissues exist for Camelops. We don't know if it had a hump, but most reconstructions choose to depict it as either humpless or having only a single, very small hump. Given that its range included the Mojave and Sonoran Deserts, a hump could have come in handy. Also, nobody can prove if it "spitted" for defense against enemies like llamas and alpacas do. Camelops disappeared at the end of the Ice Age alongside the mammoths, sabertooths, and ground sloths, ending the native camel lineage in North America for good.

The North American camels also produced a variety of intriguing species during their period of endemism, ranging from gazelle-like runners such as Stenomylus to elephant-sized behemoths like Titanotylopus. The most famous of these however was the Miocene "giraffe-camel" Aepycamelus. This animal is often called "Alticamelus" in older media: both names mean "lofty camel", but "Aepy-" is Greek and "Alti-" is Latin. It was indeed taller than the already-tall modern dromedaries (up to 3m), but not much heavier: it was slender and had especially long limbs and neck, convergent with modern giraffes. Unlike more primitive camelids, Aepycamelus had already the typical flattened toes with small hooves of modern camels and llamas, but did not have a fatty hump on its back. As Aepycamelus lived in lush grasslands, it should not have had the desert adaptations of modern camels like the ability to store fat to survive the lack of food, or to resist thirst. Interestingly, it's believed that camels originally evolved their desert adaptations to survive cold environments, as fossils of camels have been found in the Arctic dating the Late Miocene/Early Pliocene; these belonged to the genus Paracamelus, the ancestor of modern camels. The biggest known camel is the 4m-tall Syrian Camel (Camelus moreli) of the Pleistocenic Middle East, a member of the same genus that contains modern camels.

1. Entry Time: Undetermined
2. Trope Maker: Documentary media

Ancient Gnawers: Castoroides & Ceratogaulus *

It's not common to see prehistoric rodents and other usually small-sized mammalian groups, like rabbits, bats, "insectivorans",^note moles, hedgehogs, and shrews; properly called eulipotyphlans or pangolins, in popular media. However, these guys tend to be a bit more commonly seen than the others.

Castoroides ohioensis, means "beaver-form from Ohio" (Castor is the genus of the modern beaver), is popularly known as the giant beaver: indeed, it was of the same rodent family as modern beavers, the Castorids, but was as large as a small bear (three times heavier than the capybara, the largest modern rodent) and with extremely powerful incisors, possibly the most powerful ever among rodents. It lived in Ice Age North America and was thus a member of the Pleistocene megafauna, but it wasn't the biggest rodent ever — some South American rodents were as big as a large cattle or a small rhinoceros! Due to its size and massive build, Castoroides was probably rather slow-moving on land, and may have been prey for the saber-toothed cats, American lions, and dire wolves.

The main difference from modern beavers other than the size is that Castoroides was not a dam/lodge-builder (some alleged Castoroides dams have turned out to just be the centuries-long work of generations of beavers). Its incisors were not adapted for cutting down trees. Dam-building seems primarily exclusive to modern beavers; one smaller earlier castorid, Palaeocastor ("ancient beaver"), dug strange corkscrew-like burrows in the Miocene North American prairies, making it more like a prairie dog than to a beaver in size, shape, and behavior. But like modern beavers, Castoroides was a wetlands animal; evidence suggests it ate water plants, rather than the woody plants preferred by today's beavers. It also had a longer, thinner tail that looked more similar to that of a muskrat. Castoroides vanished alongside the rest of the North American Ice Age megafauna, but some believe it was preserved in Native American stories of monster beavers.

Another prehistoric rodent fairly common in docu-media is the so-called "horned gopher", Ceratogaulus. Formerly known as "Epigaulus", it was not an Ice Age animal, instead living the prairies of Miocene-Pliocene North America. It also was not related to modern gophers (family Geomyidae), but rather belonged to an extinct family of rodents: the Mylagaulids. The prefix Cerato- ("horned") indicates its peculiarity: a unique two-forked bony projection above its nose that no other rodent has ever had, recalling that of the more famous and totally unrelated brontothere Megacerops, or even that of the pseudo-deer Synthetoceras or the pseudo-rhino Arsinoitherium. This makes this critter the smallest known horned mammal of all time. Several theories exist for the horns, but the most widely accepted is that they were for defense against predators.

Apart from this, the "epigaulus" was not so different from other rodents of the past and the present: it resembled a horned guinea pig in size and shape, digging burrows with its robust forefeet like true gophers do. It's not known if it could store seeds in cheek-pouches like them, however. Interesting, Ceratogaulus was not the only small burrowing mammal to develop horns — the 1m-long South American Oligocene-Miocene armadillo Peltephilus developed strikingly similar nasal "horns" by convergence.

1. Entry Time: Undetermined
2. Trope Maker: Popular paleo-art

Giant Rhino-Wombat and Giant Koala-Roo: Diprotodon and Procoptodon *

Now we enter the realm of Pleistocene marsupials. Diprotodon optatum ("wishful two teeth in front") was related to modern wombats, but was a lot bigger: it reached the size of a rhinoceros, making it the biggest marsupial ever known. With its robust limbs and massive body, it looked a bit like a hornless rhino or small-mouthed hippo, and also like several extinct ungulates like its South American contemporary Toxodon or the much older Coryphodon (see the next folder). It is the namesake of the still-living order Diprotodontia, which contains modern kangaroos, koalas, wallabies, wombats, and sugar gliders (basically, all of Australia's plant-eating marsupials).

Australian marsupials have undergone an extraordinary case of convergent evolution with placental mammals. One major difference between the diprotodont and ungulates, other than (of course) their reproductive system, is that the former had the same rodent-like incisors seen in modern wombats. We know that Diprotodon's hide was not naked like a modern rhino or hippo, but hairy like a wombat, and it had a pouch with a backward-facing opening just like the latter. Its paws were more similar to those of a bear, and many illustrations portray this overgrown marsupial rather bear-like, like a koala or a wombat indeed. Early reconstructions tended to give it a trunk, but nowadays, it's instead shown with a koala- or wombat-like nose.

Procoptodon goliah deserved the title of "giant kangaroo" more than modern red kangaroos (Macropus rufus), the largest living marsupial. It was taller and more massively-built than both (standing over 6ft tall, as opposed to the 4ft-tall red kangaroo), with a shorter tail and more robust forelimbs. It's the biggest known kangaroo ever, and is also known as the "short-faced kangaroo" because of its flattened muzzle, which looked like a koala's. Its pouch was similar to modern female kangaroos, but its hindfeet had a single horse-like hoof each. Its body frame and limbs were much stockier than modern kangaroos, and this, together with the flat face, almost made it look like a giant ape.

Unlike modern kangaroos, which are all grass-grazers, Procoptodon was a browser of trees similar to ground sloths, using its robust forelimbs to pull down branches. Although popularly portrayed as a jumper, more recent research indicates it was too heavy to hop on two legs and instead walked in a similar manner to a human — its broad hips even supported a pair of large buttocks, an adaptation convergently evolved with us for walking on two legs for long distances. For this reason, it would have maintained a different stance from its modern relatives, keeping its heels off the ground and standing on its hoofs like a horse. We don't know at all if it "boxed" with other conspecifics like modern male kangaroos do, nor of it had the same ability to bear three cubs at different stages of development of modern female kangaroos.

These two giant mammals from the Land Down Under are more excellent examples of Mix-and-Match Critters, and the two most commonly-portrayed herbivorous prehistoric marsupials in media because of their size. They could have been portrayed even in prehistoric paintings made by the ancient Aborigines of the Stone Age, maybe even on the Uluru. Some also believe stories of these animals (as well as Megalania mentioned above and Thylacoleo below) have been preserved in Australian Aboriginal mythology.

1. Entry Time: Late 1990s
2. Trope Maker: The Prehistory of Australia (documentary)

Marsupial Felines?: Thylacoleo & Thylacosmilus *

Ice Age Australia was also home to one of the most unusual carnivorous mammals to have ever lived: Thylacoleo ("pouched lion"), nicknamed the "marsupial lion". While the first members of the genus debuted in the Pliocene, the most known species, T. carnifex, meaning "executioner", is the Ice Age one, the last and largest of them all. It was part of the family Thylacoleonidae (named after it, of course), which in turn was in the Diprotodontia order, with its closest relatives all being herbivores — the koala, the wombats, and Diprotodon. All of modern Australia's carnivorous marsupials are in the order Dasyuromorphia, thus unrelated to Thylacoleo.

The marsupial lion was so-called because its body shape, sharp claws, and short head remember modern big cats. But unlike the latter, it had rodent-like incisors (like wombats and Diprotodon) instead of the classic fangs, and "guillotines" similar to those the Paleozoic fish Dunkleosteus instead of carnassial molars. Scientists once thought Thylacoleo was herbivorous like a wombat or rabbit because of its strange teeth; they now know it was predatory, thanks to bite marks on the bones of other extinct marsupials. Not only that, it may have been the most efficient mammalian predator ever. Despite being no bigger than a jaguar, it was likely able to kill even the diprotodonts and giant kangaroos! The combination of retractable Velociraptor-like claws in its powerful forelimbs (perfect for scaling trees to ambush victims) and guillotines in its mouth proved a powerful killing arsenal, able to slice the neck of prey and deliver instant death. Were it not for the presence of two larger, faster, and equally well-armed reptilian predators — the terrestrial crocodile Quinkana and Megalania, the giant goanna — it would have been the continent's unrivalled predator. And yet despite all this, its close relationships and the unusual shape of its teeth tell us it was descended from herbivorous ancestors.

We often think of Ice Age animals as primordial beasts of a bygone era, but the truth is that they were all very modern animals adapted to today's world; virtually all living and historically-extinct animals we know of co-existed with them, including us humans, and in another timeline, the Pleistocene megafauna would still be roaming Earth today. In the case of Australia's ancient giants — the marsupial lion, the diprotodont, the giant short-faced kangaroo, Megalania, and others — it seems they all met an untimely end at the hands of the first Aboriginals, who set fires to grow different plant species, consequently starving their prey into extinction. The introduction of the dingo a few centuries later spelled the same fate for the other main mammalian predators of prehistoric Australia — the smaller thylacines (see Historically-Extinct Mammals) and Tasmanian devils. While the devils still survive today, the thylacine missed the chance to be observed by modern wildlife lovers only by a matter of decades. Forget Prehistoric Monsters, it seems that Humans Are the Real Monsters.

Moving on to a lighter topic (and way before the Ice Age), we head to the then-island continent of South America, ruled by a strange cast of apex predators — terror birds, terrestrial crocodile-relatives, and the next guys on our prehistoric tour, the sparassodonts. Though not "marsupials" in the modern sense of the term, and thus possibly lacking a true "pouch" just like some South American opossums, the sparassodonts were a closely related lineage of carnivorous mammals that converged on many placental carnivorans. Members included the bear-like Borhyaena and the weasel-like Cladosictis, but the largest and most well-known of these was the Miocene-Pliocene Thylacosmilus atrox ("atrocious pouched knife"), a marsupial sabertooth.

The same size as the marsupial lion but slenderer, Thylacosmilus had two upper fangs virtually identical to those of actual saber-toothed cats, but unlike the latter, they were ever-growing like an elephant's tusks or rodent's incisors. To protect these fangs, the lower jaw has a couple of bizarre bony sheaths covered with skin, which could have given it a curious drooping-lipped appearance. Some think even real saber-toothed cats had drooping lips to contain the "sabers" when the mouth was closed, but if they had these lips they were fleshy and not bony like those of Thylacosmilus. Traditionally, it was believed that Thylacosmilus used its sabers in the same way Smilodon did, but in 2020, studies revealed that Thylacosmilus had a decidedly un-catlike hunting style — instead of using its huge teeth to stab its victims' throats, as saber-toothed cats likely did, it probably used them to slash open their abdomens and feed on their internal organs.

The existence of the sparassodonts is testament to the "splendid isolation" South America experienced for most of the Cenozoic, not unlike Australia today. The terror birds, xenarthrans, and native ungulates discussed on this page and previously are other examples of the unusual and often convergent lifeforms that emerged at the time, along with native rodents, monkeys, and opossums. Then South America collided with its northern counterpart, forming the Isthmus of Panama and instigating the Great American Interchange. Xenarthrans, terror birds, rodents, monkeys, opossums, parrots, toucans, and hummingbirds entered North and Central America, while cats, elephants, horses, deer, tapirs, dogs, bears, raccoons, llamas, peccaries, venomous snakes, and condors came down south. Traditionally, it was believed the predatory northern invaders outcompeted the native southern carnivores, spelling the end for Thylacosmilus, but new evidence shows the sparassodonts were gone long before placental carnivores arrived, leaving the real answer a mystery for now (the terror birds briefly thrived alongside their mammalian competitors before going extinct as well, while the croc-relatives had gone extinct well before the sparassodonts did).

In old illustrations, both Thylacosmilus and Thylacoleo are often portrayed with a literal cat-like external appearance, with the same eyes, ears, body, fur, or even retractable claws of real felines, but since both weren't related with them at all, the reality of this is uncertain. Sadly, neither the giant herbivores of Australia nor the two "marsupial cats" appear in Walking with Beasts; interestingly, the producers initially planned a seventh episode with Australian Ice Age fauna — thus giving at least Thylacoleo the chance to appear — but this program never materialized.

1. Entry Time: Undetermined
2. Trope Maker: Their resemblance to big cats

A Cold Safari: the Cave Lion, the American Lion, & the Cave Hyena *

Prehistoric cats weren't all sabertooths; there were also more normal-looking ones from the subfamily Felinae (which contains all modern cats; sabertooths were in the other subfamily Machairodontinae). The former are nicknamed by paleontologists "biting cats", the latter "stabbing cats"; it's easy to see why.

The most well-known "biting" extinct cats were the American lion (Panthera atrox: atrox = "atrocious") and its Eurasian cousin, the cave lion (Panthera spelaea: spelaea = "from caves"), both formerly considered larger Ice Age subspecies of their closest living relative, the modern lion (Panthera leo), and well-adapted to live in colder climates along with the northern species of mammoths. Some think they were the main predators of ancient humans, but this is not certain. They were similar in shape and look to modern Panthera felines, but unlike modern lions — at least according to some prehistoric paintings — they had no manes. It's uncertain if their social structure was identical to modern lions, or if they were more solitary like tigers and jaguars.

In Walking with Beasts, a cave lion has a minor role in the episode dedicated to the woolly mammoths: here, it's correctly depicted mane-less (unlike in other paleo-artistic works) and imagined as living in small prides, but it also has snow-white fur, a short tail, and even small "sabers" like a "stabbing cat". A lot of these errors are due to it being a reused model of the short-sabered sabertooth cat Dinofelis from the 4th episode; in reality, the cave lion's teeth and tail were like those of every other "biting cat", and thanks to some frozen specimens, we know its coloration was like a modern lion's but paler.

The Cave Hyena is regarded today as a simple subspecies (Crocuta crocuta spelaea) of the well-known African spotted hyena (Crocuta crocuta). The cave hyena lived alongside the cave lion in Ice Age Eurasia, but compared with the more famous cave bear, both were less strictly associated with caves. The cave hyena was similar in appearance and behavior to its savannah equivalent, but with thicker fur and a stockier body against the cold. In Prehistoric Park, the cave hyenas are not CGI but live-acted by modern spotted hyenas, and it's very likely that cave hyenas "laughed" much like African spotted hyenas, given the former was a subspecies of the latter.

1. Entry Time: 2001/2006
2. Trope Maker: Walking with Beasts (cave lion); Prehistoric Park (cave hyena)

Mûmakil in Prehistory: the Columbian Mammoth and the Steppe Mammoth *

People often assume that mammoths were bigger than modern elephants. This is wrong if we're talking about the stock mammoth, the hairy, curly-tusked, tundra-dwelling woolly mammoth that everyone knows, but it is true about certain other mammoth species.

There were indeed many mammoth species in Real Life, with the Mammuthus genus having first appeared in the Pliocene. The largest ones did challenge Paraceratherium (see the next folder) for the title of largest land mammal ever, weighing 15 tons or more (comparable to a medium sauropod dinosaur), while a modern elephant and a woolly mammoth are "only" 4-6 tons (like a big ceratopsid or stegosaur). However, a paracerathere would still be taller than any mammoth thanks to its giraffe-like shape.

The most famous are the American Columbian mammoth (Mammuthus columbi; a common synonym is Mammuthus imperator, the Imperial mammoth) and the lesser-known but earlier-living and even larger Asian steppe mammoth (Mammuthus trogontherii; the ancestor of the Columbian and woolly mammoths), very similar to each other in look, and both with the typical dome-like head and hump on their shoulders shared with the woolly mammoth. Others include Mammuthus meridionalis, the southern mammoth of Southern Europe and West Asia, and Mammuthus africanavus, the African ancestor of all other mammoths — both pre-Ice Age, like the steppe mammoth. Columbian mammoths have been discovered in the famous La Brea Tar Pits along with mastodons, Smilodon fatalis, camels, ground sloths, dire wolves, and many other modern and extinct animals. Mammoth behavior was probably analogous to modern elephants, with a matriarch leading a herd and the bulls living lonelier lifestyles.

The lesser popularity of the giant mammoths (despite their size) compared to the woolly one is probably due to their more "normal" appearance. They were more similar-looking to modern elephants than to the popular image of a "mammoth" because they were mostly hairless and with straighter tusks. These tusks were nonetheless more curved than any modern elephant, and much bigger — up to 5m/15ft long and weighing 200kg or more, they were the biggest/longest teeth known so far in the animal kingdom. These tusks tended to be straight at the base and curly only at their tip, unlike those of the woolly mammoths. Only large Palaeoloxodon and some older proboscideans like Anancus had tusks of comparable size to those of male mammoths. Females of the giant mammoths had smaller tusks, like what is visible with woolly mammoths.

Giant mammoths inhabited relatively warmer climates, and their greater size was enough to preserve heat without a woolly coat. Think the mûmakil from The Lord of the Rings; okay, not quite that big (nor six-tusked), but generally similar in appearance. It's easily thinkable that the giant mammoths feared no predator as adults, like the earlier "giraffe-rhino" Paraceratherium of Oligocenic Asia.

It's worth noting that mammoths as a whole actually thrived even after the end of the Ice Age, as there was more food available. Therefore, it was almost certainly humans changing their habitat that drove them to extinction, evidenced by the fact that populations on islands lasted much longer than those in the more easily-accessed mainland areas.

1. Entry Time: Undetermined
2. Trope Maker: Documentary media and gigantic skeletons in museums

Lilliputians or Cyclopes: the astonishing Dwarf Elephants *

Among extinct members of the elephant clan, last but not least are the island-dwellers that lived in the Ice Age but managed to survive until in recorded history: the oxymoronic dwarf elephants. Yes, they were REAL, and some were even sheep-sized: true miniatures of modern elephants, like Gulliver's famous Lilliputians.

Most of them lived in the Mediterranean islands; especially famous is Palaeoloxodon falconeri (one of the "straight-tusked elephants") of Sicily and Malta, known the possible link with ancient legends from Greek Antiquity (see below). There was also Mammuthus creticus, the Cretan dwarf mammoth, and Palaeoloxodon cypriotes of Cyprus. Others lived elsewhere; Mammuthus exilis, the Channel Islands mammoth, lived on the Channel Islands off southern California was descended from the gargantuan Columbian mammoth, while Wrangel Island off eastern Siberia and Saint Paul Island off Alaska supported woolly mammoths smaller than the mainland forms (but of the same species). Additionally, dwarfs of the slightly more primitive proboscidean Stegodon existed around the same time in Celebes and Flores in Indonesia. All achieved their dwarfism due to the limited resources of island environments and the lack big mainland predators reducing the need to defend themselves with their bulk — at least until humans drove them all to extinction. As for how they ended up on islands in the first place? In most cases, they swam (elephants are excellent swimmers), while the Wrangel and Saint Paul mammoths walked there due to the lower sea levels of the Ice Age. Interestingly, the "woollies" of Wrangel and Saint Paul managed to survive until about 4,000 years ago, contemporaneous with Ancient Egypt. However, dwarf elephants still exist today — Borneo in Indonesia hosts Asian elephants smaller than their mainland and Sumatran counterparts.

There's a theory that elephant bones found in the Mediterranean were identified by the ancient Greeks as the remains of monsters, heroes, and mythical animals from the Age of Heroes. Some of these bones were identified as cyclopes, due to the alleged misunderstanding of the elephant's nasal opening, placed where cyclopes would have their one eye. This theory is doubted by some historians, as no elephant skulls have been found in the alleged areas — Mediterranean fossils are far too fragmentary due to the frequent earthquakes and volcanoes of the region preventing something as fragile as a fossilized skull to survive intact for long periods.

1. Entry Time: Undetermined
2. Trope Maker: The oddness of their size and the association with the cyclops myth

Stock Pre-Ice Age Mammals

NOTE: A few animals in this folder actually reached the Ice Age, but are here for comparison.

The Start of Horses' Evolution: Eohippus & Hyracotherium **

Now we'll go before the Ice Age and meet the so-called "horse ancestors" (more precisely, the equid ancestors). Although little-portrayed in mainstream media, they are more familiar than other pre-Ice Age mammals because they have always been among the symbols of evolution, almost as much as the dodo is the icon of extinction. Horse ancestors weren't so cool-looking compared to most other extinct hoofed mammals: they mostly resembled their modern namesake at a glance. The most famous of these forerunners are, obviously, the least horse-like of them all, averting Bigger Is Better for once, as they were also the smallest: Eohippus ("dawn horse") and Hyracotherium ("mole beast"), both Early Eocene and often considered the same animal in the past (the former was North American, the latter European).

An almost-unbelievable Science Marches On affair has actually encircled horse evolution, despite its iconic role in popular science. This evolution was not as linear as shown in popular science books and elsewhere, though it's certain that equine ancestors progressively lost their digits from four to one on each foot, their heads became loftier to see farther, their limbs became nimbler to run faster, their overall size constantly increased, and their teeth progressively adapted from browsing forest vegetation to grazing the grass of the first grasslands. Horse evolution has often been cited as a symbol of progress and improvement in general, probably due to the historical fame of the horse as a "noble" animal, that started as a small modest forest-dwelling leaf-eater... forgetting that modern animals are actually not "better" than the older ones only because they reached our time; every animal is adapted to the environment of its own period. Elephants too and their evolution have had a similar reputation of the horses' one in pop-science media, and elephants have also been classically quoted as "noble" animals in several human cultures.

While Eohippus was a true horse within the modern family Equidae, Hyracotherium was actually a much more primitive animal part of a group of horse relatives called the palaeotheriids (such as Propalaeotherium from Walking with Beasts). However, systematics of the earliest ungulates are very messy, due to how similar the earliest ones all looked, with many other early ungulates (including some rhino and tapir ancestors) being mistakenly labelled as horse-ancestors. Among modern ungulates, the artiodactylan chevrotains (mouse-deer) and duiker antelopes are perhaps the ones that most resemble these animals in size and appearance.

Whenever the putative "ur-horse" Hyracotherium/Eohippus shows up in media, expect it to be portrayed as a Red Shirt, usually falling prey to the giant flightless bird Gastornis/"Diatryma". But after Science Marches On, we know it's highly unlikely for the bird to have had any interest in the small ungulates due to its herbivorous diet — the "ur-horses" might have instead been prey for terrestrial crocodilians like Boverisuchus (aka "Pristichampsus"), being "as large as a fox terrier", to use a classic description in paleo-books. Among fictional appearances, the most notable was perhaps Ray Harryhausen's cowboys-versus-dinosaurs film The Valley of Gwangi.

1. Entry Time: 1969
2. Trope Maker: The Valley of Gwangi (film)

A Run for the Future: the Horse Ancestors *

Among confirmed horse ancestors, they make a sort of pun if read together.

The Late Eocene-Early Oligocene Mesohippus ("middle horse") of North America, still small and with three fingers for each limb, was still a forest browser like Eohippus; the North American Merychippus ("grazing horse"), also with three digits, was larger, more horse-like and grazed on Early Miocene grasslands; the Late Miocene Pliohippus ("more horse"), again North American, was very similar to a modern equine in size and shape, and had the familiar one-hoofed toe with two vestigial toes. They are the most commonly-shown in media, but there were in reality dozens of other -hippuses, almost all North American. It's important to note that Pliohippus is no longer considered the direct ancestor of modern horses as once believed, but rather part of a sister lineage with no modern descendants. Modern horses are instead descended from the Miocene-Pliocene North American Dinohippus ("terrible horse").

Also worthy of note are the Miocene-Pliocene Hipparion (meaning "pony" in Greek) and the Ice Age Hippidion (lit. "little horse"), which break the theme of having -hippus as a prefix instead of a suffix; they also break the geographic rule, the first being an Old World critter, the second South American, both offshoots of the horse family with no descendants. Remember that all modern equines descended from North American ancestors. The wild mustangs of North America are actually descendants of European domesticated horses, which are descended from true wild horses of Asia and Europe, which, in turn, originated from North American ancestors. There were also a few exceptions of the "-hippus" rule, such as Anchitherium (another Eurasian offshoot, this time a Miocene browser closely related to Mesohippus).

Oh, and all the animals above were not only the horse's ancestors, but also the donkey's and zebra's. Despite their different appearances and habits, modern equids are so closely related to each other they're all placed in a single genus, Equus — by comparison, the modern five rhinoceros species are put in four different genera: Diceros (the black rhino), Ceratotherium (the white rhino), Dicerorhinus (the Sumatran rhino), and the namesake Rhinoceros (the Indian and Javan rhinos). The genus Equus also includes two recent historical extinctions: the African quagga, a kind of zebra with incomplete stripes, and the European tarpan, the direct ancestor of the domestic horse.

Unlike Eohippus and kin, all these confirmed horse ancestors have little chance of ever appearing in non-documentary media, probably because they look more like modern horses.

1. Entry Time: Undetermined
2. Trope Maker: Portrayals of their evolutionary sequence in pop science books

Six Horns and Two Sabers: Uintatherium **

Not all fossil mammals that looked like rhinoceroses actually were, although they'll probably get identified as such in popular media. Among the most well-known is Uintatherium ("Uinta Mountains' beast"), found in huge numbers in several fossil deposits in the western USA (but also in China). Like several other early mammals, it was described for the first time during the Bone Wars — Marsh called it "Dinoceras", "terrible horn", but the animal was re-designated Uintatherium by Joseph Leidy after it turned out he described a year earlier. For some, however, it recalls more a hippo than a rhino because of its upper pair of tusks, to the point it could be renamed "the saber-toothed rhinoceros" or the "six-horned hippopotamus".

The uintathere is perhaps the most mistreated extinct mammal of them all. Expect somebody describing its appearance as "monstrous" or "scary". True, it had three pairs of giraffe-like "horns" and the two aforementioned upper protruding tusks, but, honestly, if Uintatherium were alive today, it would probably appear no scarier than an elephant, rhino, hippo, or giraffe. Also expect a crack about its allegedly slow movement and its "tiny" brain (just like what happens to Stegosaurus), and just like the stegosaur, expect the writer to cite its slowness and/or stupidity as the reason for its extinction. Though they had comparatively short limbs and feet, similar in shape to an elephant's, this wouldn't necessarily have prevented the uintathere from running with speed if necessary — again, just like modern elephants, or rhinos, or hippos.

In Real Life, Uintatherium was one of the dinocerates, a group of primitive ungulate-relatives that were among the very first mammals to reach large sizes (about as large as a modern-day rhino). Their body plan was very successful at the time, as they roamed the northern hemisphere in huge numbers for millions of years in the Early and Middle Eocene epoch, before being outcompeted by the even larger brontotheres (see below) and the first true rhinos. The uintathere is usually depicted with rhino-like hide and sideways-pointing ears, a bit like a cow; sadly, we don't have remains of soft tissues from them, so we don't know how their skin and ears really looked. Given that it was a rhino-sized mammal living in a warm forest environment, hairlessness seems more plausible. We're not sure if their six "horns" were covered in skin like a giraffe, or keratin like cattle or antelopes, either. Another notable dnocerate was the almost-identical but larger Eobasileus ("dawn king"), of the same time and place.

Rather strangely, the famous franchise Walking with… doesn't mention Uintatherium in any of its pieces, despite them having been among the most iconic early big herbivores in the Mammal Age. This could be seen as a missed opportunity to talk more accurately about these animals, also because the uintathere is scientifically better-understood than many other primitive Eocene mammals.

1. Entry Time: 1955
2. Trope Maker: Journey To The Beginning Of Time

Slingshot Horn: Megacerops, aka "Brontotherium", "Brontops", and "Titanotherium" **

Megacerops ("big-horned face") is the genus given to a very recognizable Cenozoic pseudo-rhino that has gone under many names. You might have heard of it as Titanotherium, Brontops, or most famously, Brontotherium (man, these Brontos just can't keep their names!). Regardless of name, this behemoth is the most well-known member of its group of mammals, the Brontotheres, ("thunder beasts"), also called Titanotheres ("titanic beasts"). Whereas Uintatherium was not related to any modern hoofed mammals, brontotheres were perissodactyls (odd-toed ungulates), thus distant relatives of horses, tapirs, and rhinos. The biggest brontotheres, like Megacerops, were almost Triceratops- or elephant-sized (larger than the biggest uintathere), but still smaller than other giant herbivorous mammals of prehistory, like the giant mammoths and the guy we'll see in the next chapter.

Like Uintatherium, Megacerops was also first discovered during the Bone Wars, this time by Cope, who gave it the name "Brontotherium". Unfortunately, it turned out Leidy had already given it the name Megacerops a few years prior. Megacerops had a more rhino-like appearance than Uintatherium, having one single "horn" on its nose, and no tusks. Unlike rhinos, however, the brontotheres' protrusion was solid bone instead of hardened hair, and thus its shape has preserved in fossils. The horn of the North American Megacerops was forked with round points (rather slingshot-like), while that of its Asian cousin Embolotherium, "battering-ram beast" (the brontothere in Walking with Beasts) was shovel-like. Both had notably concave heads if seen from the side, with the eyes rather near the top, and also a big hump on their shoulders like a bison. Shattered ribs on Megacerops specimens tell us they were definitely using their horns to fight each other; Embolotherium's was more fragile, so it is les certain what they were doing with them. If their horns were covered in hairy skin, naked skin, or in keratin is uncertain. Brontotheres had four digits on the front feet and three on the back, like the ur-horse Eohippus and modern tapirs (true rhinos always have three toes on each foot). Like dinocerates, we don't know if brontotheres were hairy-bodied like bovines or "naked" like typical rhinos or elephants — the latter is more likely given how enormous they were. Brontotheres roamed the open woodlands of the northern continents in huge numbers during the Late Eocene and Early Oligocene. Compared with dinocerates, they tend to be portrayed as more active and faster-running in paleo-art, and more overall similar to true rhinos, but still rather unintelligent because of their smaller brains. Note, however, that small brains doesn't necessarily mean low intelligence; after all, dinosaurs are today well-known to have been intelligent and social creatures despite having even smaller brains than those of the brontotheres and dinocerates.

Brontotheres eventually went extinct perhaps because they weren't able to adapt to the diffusion of the first grasslands, which replaced their former food sources (soft plants; grass is a very tough plant to chew). Like the uintathere, expect to see brontotheres identified as rhinoceroses in popular works. Despite this, it seems that their closest living relatives among odd-toed ungulates were horses and their kin, and not the rhinoceroses! Two brontotheres appear prominently in the first Ice Age movie: according to their appearance, they are Megacerops and Embolotherium. They fall in the Rhino Rampage trope, even being identified as rhinos in the film.

1. Entry Time: Uncertain
2. Trope Maker: Educational media

The Giant of the Giants: Paracera-Indrico-Baluchi-therium **

Here is Our Majesty, the "biggest land mammal that ever lived"; though some giant mammoths like the steppe mammoth and the giant Indian "straight-tusked elephant" Palaeoloxodon namadicus were heavier, neither were as long or tall as Paraceratherium.

Its size was really immense; it would make modern pachyderms look small in comparison. The paracerathere was 5m up to the shoulders, as tall as a Brontosaurus; reached 7.5m/24ft when holding its head high, 5ft taller than the tallest giraffe; and weighed 15 tons, as much as three elephants or three T. rexes (some earlier estimates made it even heavier than that: up to 30 tons, as much as a brontosaur!). Contrasting with all this, it had a quite slender, elegant frame: like a muscular giraffe with a long straight neck, a small hornless head, and long, slender limbs with three toes each, like a rhino — indeed, it was a close rhino relative. Its behavior was probably more giraffe-like than elephant- or rhinoceros-like, browsing the treetops and walking with long steps like a giraffe. In short, it was the mammalian equivalent to a sauropod.

It lived in Asia during the Oligocene, after Megacerops and Uintatherium, and was only the biggest member of a whole group of extinct rhino relatives: the hyracodontids, most of which were horse-sized and more similar to horses than to rhinoceroses. Our record-holder is also a prime example of I Have Many Names among prehistoric critters: now called Paraceratherium ("near-horned beast"), you might have heard of it as Indricotherium ("Indrik's beast"; Indrik is the king of all animals in Russian folklore) or Baluchitherium ("Balochistan beast"; Balochistan is a region of Asia straddling Pakistan, Afghanistan, and Iran). There are still some scientists that believe they are three distinct yet similar genera of animals, like the equally controversial Brontosaurus and Apatosaurus case.

Some think these critters went extinct because they got too large, and when their habitat dried out, they were unable to find sufficient food; but this is only a supposition. It's also speculated that they're at or near the upper limit for how big a land mammal can get; no evidence of a land mammal larger than 20-30 tons has ever been found. There's much speculation as to why this would be the upper limit, though the very long gestation periods^note a modern elephant's pregnancy lasts almost 2 years, and it's believed that both Paraceratherium and the largest of the mammoths probably took even longer to give birth are suspected to be a major factor. This results in low birth rates that make it more difficult for huge mammals to recover from any major population loss. Anyway, like Megacerops and Uintatherium, the indrico/paracera/baluchithere was well adapted to its environment, though its lineage was relatively short-lived compared the true horned rhinoceroses that have reached our days with five species.

A young "indricothere" is the main character of the third episode of Walking with Beasts. To indirectly illustrate how big the adults of its species are, the beginning of the episode shows its mother defending it just after it's born against a pack of Hyaenodons (see below), the latter being described as "as big as rhinos" but still appearing tiny next to the adult indricothere. Indricotheres also appear huge confronted with the neighboring chalicotheres and entelodonts, even though both mammals were taller than a human and weighing more than one metric ton; at the end of the episode, the teenage indricothere is bigger than an adult entelodont, and easily chases it away from the scrubs nearby.

1. Entry Time: Undetermined
2. Trope Maker: Its size

Shovels and Spears: Platybelodon & Anancus *

Let's return to extinct elephant relatives: there were A LOT of them in prehistory, not just mammoths and mastodons. Many of them were even cooler-looking than those two, though all (except the most primitive, such as Moeritherium below) shared a similar shape to a modern elephant, with long pillar-like limbs, short feet with round nails, short necks, small tails, and compact bodies. It was their mouths and teeth that were very different.

The most infamous is doubtlessly Platybelodon, a staple of clickbait articles and videos on prehistoric life. Living across Africa and Asia during the Middle Miocene, it resembled a cross between an elephant and a hippo, with its huge mouth opening and shovel-like lower jaws; a pair of tusks were visible both in the upper jaw and in the lower. A similar beast was the widespread Miocene-Pliocene genus Gomphotherium, which had longer and pointier lower tusks compared to Platybelodon, earning it comparisons to the mûmakil from The Lord of the Rings. Whereas Gomphotherium was the namesake of the gomphotheres, Platybelodon, once thought to be closely related, was one of the ambelodonts, or "shovel-tuskers", for their short, spade-like lower tusks. One Late Miocene North American gomphothere, Gnathabelodon, lacked the lower tusks entirely, but kept the shovel-shaped jaws, earning it the nickname, the "spoon-billed mastodon". Even the primitive elephantid (thus in the same group as mammoths and modern elephants) Stegotetrabelodon widespread in the Old World during the Late Miocene/Early Pliocene, had very long and pointy lower tusks, literally resembling a four-tusked elephant. The similarly aged and distributed Primelephas, the direct ancestor of mammoths and modern elephants, had much smaller lower tusks. Many ancestral proboscideans, like Palaeomastodon and Phiomia (both Early Oligocene Africa), also had similar arrangements; the latter lacking lower tusks entirely.

Many of these animals are often shown with bizarre flat trunks to accommodate the shape of the lower jaw, but this is unproven — trunks have no bones, so they don't fossilize. However, studies suggest Platybelodon and the rest all had normal cylindrical elephant-like trunks instead, as the upper tusks show signs of wear that complement a flexible modern-styled trunk. As for the lower tusks, it was once believed they used them to scoop up water plants, but signs of wear on them indicate they were more likely being used to dig up ground-level vegetation like a literal shovel. Many of these animals are popularly called "mastodons", but none were closely related to the American mastodon.

Other "mastodons" looked more like modern elephants, lacking the lower tusks of the older kin. But even they would appear unusual to modern eyes: the Pliocene Old-World genus Anancus, had extraordinarily long and straight tusks that jutted out forward like spears. Likewise, Stegodon, had huge parallel tusks so close to each other that illustrations show the animal as obligated to keep its trunks to the side of both tusks! Both of these animals were among the closest relatives of modern elephants and mammoths, and the latter was widespread in Asia during the Ice Age. Also living in the Ice Age were the last of the gomphotheres, Cuvieronius and Notiomastodon, both of which lost the lower tusks and elongated jaws of their older kin. But while they were more "normal"-looking than previous gomphotheres, they both managed to reach South America — something no other proboscidean had achieved.

1. Entry Time: undetermined
2. Trope Maker: Their jaws and tusks

Forked Jaw: Deinotherium *

A more primitive proboscidean lineage were the deinotheres, whose namesake is their most famous member: Deinotherium ("terrible beast"). Unlike Platybelodon, Deinotherium had only two tusks like modern pachyderms.. only they grew from the lower jaw like a two-pronged fork, and were curved downward. The function of these tusks is still uncertain: possibly stripping the bark from trees, or fighting against individuals of the same species.

Several species of Deinotherium are known across the Old World from the Miocene to the Early Pleistocene, just before the Ice Age, but the two most notable are D. giganteum and D. bozasi. D. bozasi existed in Africa alongside the first humans and was the very last Deinotherium species before they went extinct. D. giganteum, on the other hand, roamed Miocene and Pliocene Europe, and was the largest of its kind, as big as the aforementioned giant mammoths (D. bozasi was no bigger than a modern Asian elephant). As a whole however, Deinotherium had longer limbs than modern elephants and was taller at the shoulders than at the hips, much like a giraffe. Its tail was small, and apart from the head, Deinotherium looked like modern elephants despite their extreme primitiveness among proboscideans — a great case of convergent evolution with the other giant proboscideans.

Due to how primitive Deinotherium was (to the point that some old studies didn't even consider it a true proboscidean!), we don't know if deinotheres shared a lot of the behaviors elephants and mammoths have, like going through musth or trumpeting. Since they were part of the same family as modern elephants, it's highly probable that mammoths did trumpet, and studies have proven they underwent musth too. We also don't know how Deinotherium's ears or trunk were shaped; some have suggested it had an extremely short, stubby trunk, but that has raised the question of how it would have been able to drink. Similarly, we don't know how much hair extinct proboscideans had on their bodies (if any) — given how big the biggest ones were, hairlessness seems likely.

1. Entry Time: 1864
2. Trope Maker: Journey to the Center of the Earth

A Dinosaur of a Whale: Basilosaurus **

The first whales evolved early in the Mammal Age, in the Eocene, from terrestrial ancestors related to modern even-toed hoofed mammals (especially hippopotamuses). Most early cetaceans were medium-sized, but not Basilosaurus cetoides ("whale-like king lizard"). This one reached the length of a modern baleen whale or sperm whale: up to 20m/60ft, longer than most stock marine reptiles — though still much shorter than a blue whale. In spite of its length, the basilosaur weighed "only" 20 tons, less than shorter modern whales like the 30-ton humpback: this is because it was much slenderer, to the point that it's sometimes described as "eel-like". But wait, why does its name end in -saurus?!? Well, when first discovered by American paleontologist Richard Harlan, its elongated shape was misidentified as a mosasaur-like reptile: hence its strange-sounding name. There was an attempt to rename it Zeuglodon ("yoke tooth") to fix the error, but nomenclature rules prevented that.

Its first remains were discovered in North America in the 19th century, and more were found in the 20th century in Egypt, which at the time Basilosaurus lived was mainly occupied by a shallow sea. For a long time, the basilosaur was one of the few early cetaceans known by science. Other early whales, like Pakicetus and Ambulocetus (see below), were discovered only during or after The '80s, along with more modern whales like Odobenocetops and Livyatan melvillei (see below). In Basilosaurus' time, all whales were still active hunters, like modern orcas and sperm whales, but still with differentiated teeth: the anterior ones pointed, the posterior serrated, an old legacy that betrays their origins from land mammals.

Basilosaurus was at the centre of a peculiar hoax in the 1840s by the notorious huckster Albert Koch. Koch had come into possession of a large number of Basilosaurus fossils, the remains of at least six different individuals, which he assembled into a 114ft-long amalgam he dubbed "Hydrarchos harlani" ("Harlan's Water King"). Koch presented his creature as a real-life Sea Serpent and the inspiration for the biblical Leviathan, until after naturalist Jeffries Wyman correctly identified it as the hodgepodge of whale bones it was. Undeterred, Koch toured across Europe and USA with his "Hydrarchos", eventually selling it off to Kaiser Wilhelm IV of Germany. Koch's "Hydrarchos" was destroyed during WW2 by Allied air raids on Berlin; a second "Hydrarchos" he made after selling off his first one was lost in the Great Chicago Fire. Koch had previously pulled off a similar hoax with his 32ft-long mastodon amalgamation "Missourium", even twisting the tusks to point upwards and make it look scarier.

Basilosaurus, with its size, was likely the top predator of its oceans, potentially preying on every other creature in its world — fossils of its smaller relative Dorudon have been found with bite marks attributed to it. However, Basilosaurus may have been a less able swimmer than modern cetaceans because of its primitiveness, maybe more similar in swimming style to a seal than to a modern whale. It also lacked adaptations for deep diving, forcing it stay near the surface of in shallow water. Since soft remains have not been preserved, we don't know if the basilosaur's tail fluke was already identical to modern whales/dolphins, or smaller and/or shaped differently, nor if it had a dorsal fin. Unlike modern whales, it retained the tiny remnants of its hindlegs, which were maybe used to lock mating pairs' bodies together).

Basilosaurus has been a recent hit in documentary media since the 1990s and especially the 2000s; see Walking with Beasts and Sea Monsters for example. However, it hasn't received the same amount of attention in broader popular culture as other giant sea critters of the past, like Elasmosaurus, Megalodon, and Mosasaurus. Its serpentine form however has been of great interest to cryptozoologists, with many proposing modern sea serpent sightings to be of surviving Basilosaurus or its descendants.

1. Entry Time: 2001
2. Trope Maker: Walking with Beasts

Mysterious Giant Skull: Andrewsarchus *

Andrewsarchus means "Andrews' ruler" and is quite possibly the most enigmatic fossil mammal known. As its complete name suggests (Andrewsarchus mongoliensis) it was discovered in Mongolia during the same American expedition led by Roy Chapman Andrews (hence the name) in which Velociraptor was first found.

Living during the Middle Eocene, only a single skull is known from this beast — and what a skull it is! At about 1m/3ft long and vaguely wolf-like in form, the sheer size of Andrewsarchus' head has classically led to it being called the largest carnivorous land mammal ever. Unfortunately, because its known from the skull and nothing else, there isn't any hard proof of that; it might have been omnivorous instead, and of course its overall size can only be guesstimated. It is often depicted as a scavenger of large herbivores' carcasses, but has also been shown as an active hunter.

Andrewsarchus was traditionally considered to be one of the mesonychians, a group of primitive ungulate relatives that evolved to be predators and were once considered the ancestors of whales. As a result, its typically shown to be a giant, wolf-like beast with primitive hooves, similar to the much smaller but scientifically better-known mesonychian archetype Mesonyx (we'll get to that guy later). However, later studies indicate that it might have actually been a close relative of the entelodonts (again, see later), thus placing it within the modern group of even-toed ungulates. However, until more fossils of this animal are found, any phylogenetic placement will only remain tentative.

Andrewsarchus memorably appeared in its traditional mesonychian form in the Basilosaurus-centric episode of Walking with Beasts. However, everything about its appearance in that show, from its size to its behavior to its overall body shape are entirely speculative and without strong fossil evidence. The hype and Wild Mass Guessing surrounding Andrewsarchus might remind one of the stories behind the dinosaurs Deinocheirus and Therizinosaurus — both also from Mongolia and long touted as unknowable giant killers until some incredible fossils showed them to be far weirder than what anyone could have expected. Let's hope the same happens with Andrewsarchus sooner or later.

1. Entry Time: 2001
2. Trope Maker: Walking with Beasts

Elephant or Pig?: Moeritherium *

How did elephants look when they were just starting to evolve? Not really like pachyderms. The most classic ur-elephant is Moeritherium, found in Egypt in the Late Eocene. It's been called "the first elephant", but some proboscideans were even more basal: ex. the fox-sized Eritherium is the most ancient proboscidean currently known, from Paleocene Morocco.

Moeritherium (" beast from Lake Moeris") was no bigger than a large pig and had four short tusks, a pair in the upper jaws and another in the lower ones. It had also hippo- or tapir-like limbs and possibly pig-like or tapir-like snout, and was definitively more like a tapir than an elephant in appearance. It also multiple cheek-teeth in its jaws like a typical mammal, unlike the single giant cheek-tooth for each half-jaw that modern elephants and mammoths have. Living in coastal swamps and estuarine environments, the moerithere is often thought to have been an amphibious animal a bit like a modern hippopotamus or a tapir, but its actual lifestyle is still unknown. As shown in Walking with Beasts, it lived alongside the giant early whale Basilosaurus, with the latter even making a failed predation attempt on it.

Like the ur-horse Eohippus, Moeritherium has often been shown in textbooks as the start of the evolutionary trip of its group, the proboscideans, passing through deinotheres, mastodonts, gomphotheres, stegodonts, etc. and ending with modern elephants and mammoths (although they do not form a straight line, instead being a radiation of multiple lineages). Its look tends to vary a bit in classic paleo-art: some depict Moeritherium as a sort of boar-thing with dense hair, while others show it naked-skinned and more looking like a hippopotamus, and usually but not always with an elephant-like short trunk and the four short tusks.

1. Entry Time: Undetermined
2. Trope Maker: Textbooks portraying elephant evolution

An Incredible Headgear: Arsinoitherium *

As previously seen with Uintatherium and Megacerops, the early part of the Cenozoic produced a lot of pseudo-rhinos. Perhaps the most peculiar, and at the same time one of the most striking-looking, was Arsinoitherium.

Arsinoitherium means "Arsinoe's beast": Arsinoe was an Ancient Egyptian queen. It is sometimes misspelled "Arsinotherium" without the "i" in the middle because so it's easier to pronounce. Arsinoitherium lived in Africa during the Late Eocene and Early Oligocene, after Uintatherium but contemporaneous with the North American brontotheres, and was of similar size and body shape to the former. Its classification has long been an enigma, but today, it is considered one of the afrotheres, making it a cousin of elephants, manatees, hyraxes, and the aardvark. Specifically, it belongs to extinct subgroup known as the embrithopods, being the last and largest of this poorly-known lineage.

Arsinoitherium's most visible peculiarity is by far its quadruple horns — an enormous pair above the nose and a second tiny knob-like pair over the eyes (the latter resembling the ossicones of a giraffe). Composed of solid bone and possessed by both males and females, they were most likely used for defense; we don't know if they were covered in keratin like with cattle or in skin like with giraffes. A lesser-known arsinoitherian peculiarity is its teeth: they were more numerous than in most four-legged mammals (though similar to cetaceans), and not clearly differentiated into incisors, canines, and molars. An inhabitant of forests and swamps, its fossils have been recovered from the same ancient coastal mangroves that produced elephant-ancestors like Moeritherium. This, combined with its short robust legs ending with "hooflets", has led some to speculate it was an amphibious animal, making it like a cross between a rhino and a hippo.

Arsinoitherium was portrayed in the Walking with… spinoff Sea Monsters, and like Moeritherium, it showed up in the episodes focused on the predatory whale Basilosaurus. In the show, Arsinoitherium is shown with a short trunk like a tapir, and thus looking simply like a bigger, horned version of Moeritherium. While the trunk helped to emphasize to viewers that it was a cousin of elephants, it is unfortunately improbable, as the shape of its skull's nasal openings lack any points of attachment for a trunk, even a small one. We also don't know if it was naked or hairy, although its size and the warm climate it inhabited point to the former.

1. Entry Time: Undetermined
2. Trope Maker: Its horns

Gorilla-Horses or Sloth-Bears?: Chalicotherium & Moropus *

The chalicotheres (sometimes known as their German name, "krallentier") are typically regarded as some of the best examples of a Mix-and-Match Critter among prehistoric mammals. They all had the head of a horse (but without the strong incisors), the body shape of a gorilla, and bear-like forelimbs with hooked claws for pulling down branches and feeding on the tasty leaves. Some nickname them "gorilla-horses" or "sloth-horses", comparing them with therizinosaur dinosaurs, ground sloths, large apes, or even panda bears.

Like sloths, chalicotheres probably weren't especially fast runners compared to other ungulates due to their frame (yes, they were ungulates!), with short hindlegs and longer forelegs (the latter being up to twice the length of the former). Nonetheless, they were powerful and muscular animals (the biggest were 3m tall and weighed about two tons) and arguably not an easy target for even the biggest mammalian predators. We don't know how long/dense their hair was, or if they had it at all, as with almost all prehistoric mammals — except those found frozen in ice.

A very successful group of hoofed mammals, chalicotheres, despite their un-ungulate-like appearance, were perissodactyls or odd-toed ungulates, distantly related to horses, rhinos and tapirs (like the aforementioned brontotheres). Their body plan however was quite heavily modified from the original ungulate shape — more so than any other ungulate except for obviously the cetaceans, which descend directly from land artiodactyls or even-toed ungulates — with claws instead of hooves. The two most well-known chalicotheres are the Early Miocene North American Moropus and the Late Miocene Asian namesake Chalicotherium. Together, they represent the two main lineages of chalicotheres — the chalicotheriines and the schizotheriines. Moropus (lit. "silly foot" because its nails had a split in the middle) was a schizotheriine, and as such, had a more horse-like appearance, walking on its claws in the same way normal ungulates do with their hooves. Chalicotherium, as a chalicotheriine, knuckle-walked like a gorilla to protect its claws against damage, just like modern giant anteaters do.

Chalicotheres roamed for a long time in Asia, Europe, Africa, and North America, lasting from the Eocene to the Pleistocene. The last species, the chalicotheriines Hesperotherium and Nestoritherium, lived in the forests of China and Southeast Asia during the Ice Age, while the last schizotheriine, Ancylotherium (shown in Walking with Beasts), existed just before the Ice Age in Africa, alongside the first humans. However, some think the infamous "Nandi bear" cryptid that allegedly lives in modern African rainforests is a surviving chalicothere.

An unnamed chalicothere (based on Chalicotherium itself) is portrayed in the third episode of WWB as a rather torpid animal with a very giant panda-like face, that makes it look more harmless than other, more badass popular representations of chalicotheres. Here, it mainly appears as fodder for other large mammals of the time — the predatory Hyaenodon and the scavenging entelodonts, to be precise — while being mostly overshadowed by the colossal Paraceratherium. Moropus, on the other hand, is one of the star animals of the Nigel Marven-narrated documentary Forgotten Bloodlines: Agate Springs, alongside the next animal on this list, the giant entelodont Daeodon.

1. Entry Time: 2001
2. Trope Maker: Walking with Beasts

Giant Hippo-Boar?: Daeodon *

We jump from odd-toed ungulates to even-toed ungulates, and this time with another unusual, iconic group, and very different-looking of extinct hoofed mammals that has achieved some popularity: the entelodonts, popularly nicknamed "hell pigs" or "terminator pigs".

Living in Europe, Asia, and North America from the Late Eocene to the Early Miocene, entelodonts ("complete teeth"; formerly called the "elotheres") had the same overall body plan as pigs but usually with a hump on their shoulders like bison. They were once thought to be closely related to pigs, but are now understood to be closer to hippos (incidentally, also thought to be pig cousins) and whales. The biggest were buffalo-sized, and the bony knobs on their massive heads and jaws made them resemble giant warthogs. But their tusks were straight like those of peccaries, much smaller than a warthog's or a babirusa's, and didn't protrude out of the mouth. The exact shape of their snout is unknown, but it's unlikely that they had pig-like noses as shown in classic paleo-art, especially given their new classification as hippo relatives.

The food habits of these critters are almost certainly like those of pigs. Their huge teeth display wear patterns consistent with omnivorous mammals: their strong jaws were able to crush the bones of corpses to reach the softer marrow inside, and their vegetarian options likely included leaves, nuts, fruits, and branches. And while certainly capable of scavenging by driving away small predators from their kill, bite marks on herbivores that shared their environment (including early camels, rhinos, and horses) suggest the possibility of active predation being part of their lifestyle. One remarkable find from Early Oligocene North America preserves multiple partially eaten remains belonging to the early camel Poebrotherium stashed in a burrow and covered in bite marks attributable to the entelodont Archaeotherium. Entelodonts' cheek teeth were flat like those of a horse or a bovine, and their incisors were small, just like modern pigs, peccaries, tapirs, and hippos. The bony knobs on their heads may have protected them against rivals during fights, as scars on the skulls of some specimens indicate they engaged in some brutal matches. They probably could open their mouths much wider than boars, but not to the same degree as hippos, which can open their mouth almost 180 degrees!

Daeodon ("dreadful tooth"; also called Dinohyus, "terrible pig") was last of the entelodonts, as well as the largest and historically the most-often depicted entelodont, living alongside the chalicothere Moropus in Early Miocene North America (featured in Forgotten Bloodlines: Agate Springs, where Daeodon is one of the focus animals alongside Moropus). Daedon-like creatures appear in The Lord of the Rings: The Rings of Power, and are accurately portrayed for a fantasy show. They are bigger than humans, have a boar-like even-toed ungulate appearance, hooves, and even the bony knobs entelodontids are known for. Yet in universe, they are referred as wolves and are supposed to be related to the canid wargs. Other notable species include the previous mentioned Archaeotherium ("ancient beast") of Late Eocene-Early Oligocene North America and the group's namesake, Entelodon of Late Oligocene Asia. The former was one of the smallest entelodonts, the size of a modern boar; the latter was more similar in size to Daeodon.

Walking with Beasts depicts showed an unnamed Asian entelodont (identified as Entelodon in some sources, but likely its even bigger relative, Paraentelodon) living alongside Paraceratherium. However, the opening of its mouth is exaggerated and its cheeks and lips are reduced to make it seem uglier and scarier — emphasized further by its behavior and the narration characterizing it as a vicious brute. Additionally, the entelodonts also appear almost naked like a warthog, but we don't know if entelodonts were like this or if they had fur. Extinct true pigs include the Late Miocene "unicorn-pig" Kubanochoerus and the giant Ice Age warthog Metridiochoerus, but see Prehistoric Life - Mammals for these.

1. Entry Time: Late 1980s
2. Trope Maker: Dino-Riders (identified as "giant warthogs")

Spectacular Heads: Sivatherium & Synthetoceras *

These mammals were also artiodactyls, but similar to deer or moose in shape. Sivatherium giganteum was one of the biggest ruminants ever; it was heavier than an average bison, and 2.5m tall at the shoulder — as massive as a giraffe, though less tall. Its name means "Shiva's giant beast".

Sivatherium was indeed related to giraffes, but little resembled them. Stocky and short-necked, it looked more like a huge okapi, except with "antlers" quite similar to a moose's; these "antlers" were true ossicones like those of a living giraffe, firmly attached to the skull as seen in the Sivatherium's surviving relatives. Being a ruminant, it arguably "chewed its cud" like a cow or a giraffe in life. Though it cannot be proven because soft tissues cannot be preserved for so long, it is assumed to have a had the same prehensile tongue as its living relatives. Sivatherium first appeared in the Pliocene and survived into the Ice Age, living in both India and Africa (the African ones were initially identified as its own animal Libytherium); some think it's represented in ancient rock paintings in the Sahara and India, and alleged depictions have even been recovered from Ancient Sumeria. Many other extinct giraffe-relatives existed in the Cenozoic across Europe, Africa, and Asia: together, the form the family Giraffidae, of which only two members have survived to today: the proper giraffe and the okapi, both exclusive to Africa, where the family first evolved before spreading into Europe and Asia. Interestingly, most of them look more like the okapi, with the giraffe being a much more specialized member of the group — not all "oddball" members of a group of animals are prehistoric! Contrary to popular belief, the giraffids are not distinguished by their ossicones, which have been found in extinct non-giraffid mammals, but by their teeth; giraffids are the only animals to possess bilobed canines, which are essentially two teeth with a single root. Even the okapi was identified as a giraffid by these teeth when physical specimens were finally found; the people searching for it were expecting first a forest zebra, then an unidentified antelope before the teeth and their implication took them by surprise.

Synthetoceras tricornatum ("three-horned fused horn") has traditionally been more enigmatic. From Late Miocene North America, it resembled in shape a common deer or antelope, but had indeed three horns placed on the head surprisingly similarly to a Triceratops, although the nasal horn was long and Y-shaped like that of Megacerops, albeit with pointed ends like a kitchen fork. Its size was more normal, like a big modern antelope. It was arguably a faster runner than the giant sivathere, probably able to jump easily like a deer or a wildebeest. Despite all this, this "mammalian Triceratops" was part of a now-extinct group called the protoceratids: no one is sure what this unique North American family of artiodactyls is related to, but they've been suggested to be cousins of either the camels or the chevrotains/mouse-deer. Either way, since camels and mouse-deer both ruminate like true ruminants (cattle, giraffes, deer, sheep, and antelopes), Synthetoceras almost certainly did the same. Another frequently depicted protoceratid is the Early Miocene Syndyoceras cooki, which had similar brow horns but a smaller V-shaped pair on the snout. The last protoceratids vanished in the Early Pliocene, well before the Ice Age. As with the above-mentioned Sivatherium, Synthetoceras may be wrongly identified as a true deer or antelope in media — although like them, only male protoceratids had horns.

In older depictions, Sivatherium was more moose-looking than in the modern ones, in which it's often painted with the same colors of a modern giraffe or a modern okapi. Synthetoceras, on the other hand, can be either represented as deer-like or antelope-like according to the artist. But unlike deer, the "syntheto" had perennially-attached horns on its head, more like an antelope. The prominences of both Sivatherium and Synthetoceras were probably covered in skin, like the ossicones of a giraffe (deer antlers are naked bone covered by hairy skin only at the start of their periodic growth, while the horns of antelopes are bony cores covered in keratin).

1. Entry Time: Undetermined
2. Trope Maker: Their head-prominences

Early Hooves: Coryphodon & Phenacodus *

Among the earliest mammals traditionally classified among the "ungulates", these two have been among the relatively most common in popular paleo-media.

Coryphodon was one of the biggest mammals of the Early Eocene, the size of a large cow. It lived roughly alongside the famous bird Gastornis, as well as Eohippus and Uintatherium, in North America. It was very similar to a hornless uintathere, with small tusk-like canines like the latter, and is classically compared with a hippo. Because of this, Coryphodon was once considered an early ungulate-relative; in actuality, it was a member of the extinct pantodonts, an extremely basal Paleocene-Eocene group composed of the first large, plant-eating land mammals, with Coryphodon being one of the biggest members. Though smaller than other later herbivorous mammals, an adult coryphodont probably feared no predators except for perhaps large crocodilians. Classic portraits often show the coryphodont as amphibious like a hippopotamus, but it could have been more terrestrial. It was often believed slow and had actually a very small brain, but again, this doesn't mean it was harmless and/or witless.

Phenacodus was much smaller (about the size of the better-known Eohippus), and also lived in the Early Eocene. It was very generic, with dentition suited for various foods (probably was a mainly-herbivorous omnivore), and with an archaic long tail typical of the earliest "hoofed mammals". It was formerly considered part of a group of primitive ungulates known as "condylarths", but this order has been disbanded; Phenacodus is now thought to have been a relative of the perissodactyls or even a true primitive member of this group. When the giant bird 'Gastornis/"Diaryma" was believed to have been the superpredator of the Early Eocene, Phenacodus was considered one of its possible prey, just like Eohippus''.

1. Entry Time: Undetermined
2. Trope Maker: Media portraying the early Mammal Age

Meat-Eaters, but not Carnivores: Hyaenodon & Sarkastodon *

Although "carnivore" literally and commonly just means "meat-eater", in cladistics, it refers to members of the order Carnivora (the less ambiguous term for members of this group is "carnivoran"). The vast majority of large carnivorous land mammals are carnivorans — bears, dogs, cats, hyenas, weasels, seals, etc. — but there have been exceptions: not counting marsupials like the pseudo-feline Thylacoleo, there were also the creodonts, composed of the hyaenodontids and the oxyaenids.

Creodonts (meaning "meat tooth") were related to true carnivorans, but were more primitive. They had smaller brains (like most early mammals), larger skulls, and different cheek teeth than true carnivorans; they nonetheless often had powerful jaws with a stronger bite than modern carnivores. They thrived across Europe, Asia, Africa, and North America during the first half of the Cenozoic, finally vanishing in the Late Miocene from their last strongholds in Africa and India. It is widely believed they were outcompeted by true carnivorans.

Hyaenodon (often misspelled "Hyaenadon", "Hyenodon", or "Hyenadon"), the most iconic and portrayed creodont in media, has a name that is not mere coincidence: despite being more similar in shape to a short-limbed, long-tailed, big-headed wolf, it had the typical crushing jaws/teeth of a hyena — hence the name, "hyena tooth". Scientists once thought the hyaenodont was a scavenger because of this, but since Real Life spotted hyenas are more often active hunters, contrary to popular belief, the bone-crushing jaws of their ancient namesake don't rule out more predatory behavior. Over 30 species of Hyaenodon existed, ranging from the size of a weasel to the size of a bull and living across Eurasia and North America from the Middle Eocene to the Early Miocene.

The third episode of Walking with Beasts features the biggest Hyaenodon, the Asian H. gigas, exaggerated to the size of a rhino and as the main predator of the story, capable of killing with extreme ease two-ton chalicotheres, and digesting even their teeth — based on modern hyenas, which can dissolve bones in their stomachs. The last claim is mere speculation: note that most modern meat-eating mammals can't digest bones, much less enamel-covered teeth. It may also have been shown as more agile than it was in Real Life, since a large specimen of Hyaenodon was arguably rather slow-moving compared with modern wolves, cats, or hyenas, not only being heavier but also having shorter feet. The Hyaenodon of WWB is also given a lot of dog/wolf-like behaviors even growling in the same manner as an Angry Guard Dog when approaching the young indricothere in a pack — again, there's no proof of wolf-like pack behavior or even growling.

Note also that other creodonts were even bigger than the biggest hyaenodont, ex. the half-ton Megistotherium ("huge beast"), which hunted elephants on the plains of Early Miocene Africa (proven by the presence of its bite marks on their bones). The older Sarkastodon (also meaning "meat-tooth", like creodont does) lived in Asia during the Middle Eocene and was bigger than both Hyaenodon gigas and Megistotherium at nearly one ton. Like the hyaenodont, we don't know much of its lifestyle apart from the fact that it was specialized for meat-eating; it likely hunted early rhinos and dinocerates by ambush as it would not have been very fast. However, there is the possibility, however, that like many modern carnivorans (such as bears, raccoons, and skunks), these giant creodonts were not pure flesh-eaters but omnivores instead.

1. Entry Time: 2001 (Hyaenodon); 2010s Sarkastodon
2. Trope Maker: Walking with Beasts (Hyaenodon); Jurassic World: The Game (Sarkastodon)

Cat and Dog Mimics: Eusmilus & Amphicyon *

Other extinct mammals were true carnivorans: all carnivorans can be divided into two groups — the caniforms (dogs, bears, seals, raccoons, weasels, etc.) and the feliforms (cats, hyenas, mongooses, etc.). And while all many extinct carnivorans fall into these lineages, many deceptively looked like members of the modern families.

Eusmilus ("true saber"), for example, was an almost-perfect copy of a saber-toothed cat in shape, size, and anatomy. However, it actually belonged to a distinct lineage of feliforms called the nimravids, or "false sabertooths", which also included Nimravus, Dinictis, and its possible synonym Hoplophoneus. Eusmilus lived earlier than the true sabertooths during the Late Eocene and Early Oligocene in North America, sharing its environment with the three other nimravids mentioned prior, as well as brontotheres, entelodonts, creodonts, and primitive horses, camels, rhinos, dogs, and rabbits. Like all nimravids, Eusmilus had shorter legs and tails than real cats and walked on the soles of its feet like a bear instead of on its toes like a cat. Eusmilus also had particularly long sabers, almost as long as Smilodon's and longer than most other nimravids and most other true saber-toothed cats. The behavior and predation style of nimravids are uncertain; some say they were less intelligent than true cats, but that's only a guess, obviously. Nimravids were widespread across Europe, Asia, and North America from the Middle Eocene to the Late Miocene, likely going extinct as a result of grasslands replacing its wooded habitat and competition with modern cats.

Amphicyon means "half-dog", an apt term because it was related to canines but was not one of them — it's the namesake of its own family of caniform carnivores, the amphicyonids, or "bear-dogs". Amphicyon was rather in the middle between a long-tailed wolf and a slender bear, possessing the flat-footed, or plantigrade, posture of the latter (dogs walk on their toes, in a digitigrade posture). Over two dozen species of Amphicyon are known across Miocene Europe, Asia, and North America, but the most infamous is the massive A. ingens, the apex predator of Middle Miocene North America. Bear-dogs were widespread across the three abovementioned continents and Africa from the Middle Eocene to Late Miocene, but the cause of their extinction is currently unknown. They should not be confused with the "dog-bears", or hemicyonines, a Miocene subfamily of bears that evolved towards being fast-running pursuit predators.

1. Entry Time: Uncertain
2. Trope Maker: Popular media about Cenozoic animals

Straight from the Pit: Leptictidium, Eurotamandua & Eomanis *

Leptictidium is probably the most famous of the mammals preserved in the Messel Pit of Germany, which during the Middle Eocene was a tropical rainforest surrounding an anoxic lake. While many are familiar creatures, including early pangolins, hedgehogs, bats, horses, rhinos, rodents, marsupials, and primates, Leptictidium was the most peculiar of them all. About the size of a cat, it looked like a small kangaroo or jerboa, but the modern animal that most resembled it is maybe the sengi, or elephant shrew, of Africa. However, Leptictidium was not related to any modern mammalian group; formerly considered an "insectivoran" (the group containing hedgehogs, moles or shrews), it is today placed in the eponymous leptictids, a group of extremely primitive placental-relatives that first appeared when the nonbird dinosaurs were still ruling the Earth. Lepticitidium is the largest of this group, and its kin would last until the Oligocene.

Arguably because of its Mix-and-Match Critter look, Leptictidium was chosen as the main character of the first episode of Walking with Beasts, set in Eocene Germany. However we don't know if it actually hopped like a kangaroo like in WWB or ran like a miniature dinosaur; some portrayals prefer the first choice, others the second. Additionally, we don't know if it had a tiny trunk, like seen in the show. Anyway, judging from its teeth, it was arguably a predator of insects or small vertebrates.

The Messel Pit has produced countless exquisite fossils — whole skeletons complete the fur, feathers and, "skin shadows" (such as the wing membranes of early bats); not to mention ants the size of hummingbirds, turtles caught in the act of mating, thousands of fish and insects (some still with color!), over 30 distinct plant species (including prehistoric grapes and walnuts), and even evidence of the infamous cordyceps fungus zombifying ants. All this can be attributed to the anoxic lake; animals that fell in and drowned were preserved in conditions hostile to decomposers and scavengers (caused by toxic volcanic gasses at the bottom of the lake that would periodically erupt, as shown in WWB), thus allowing them to remain in pristine condition.

Among the mammals of Messel, two of the most notable are members of a very ancient group: Eomanis and Eurotamandua are the first known pangolins. As expected from Messel animals, their remains include soft parts of their body. Their shape was already that of their modern relatives, with long muzzles, short legs, robust claws, long tails, and a long sticky tongue to catch ants and termites. However, their external look was very different from each other: Eomanis had the familiar tile-like scales covering most of its body, and was virtually identical to modern pangolins; Eurotamandua was hairy and resembled more a modern South American anteater than a pangolin — indeed, it was long classified as a proper anteater (which have only ever lived in South America). The names of both animals are referred to this older classification: Eomanis means "dawn pangolin”, Eurotamandua means “European tamandua” (Tamanduas are medium-sized anteaters). Pangolins were once considered xenarthrans like the sloths, anteaters, and armadillos, but today, they are considered cousins of the carnivorans.

1. Entry Time: 2001 (Leptictidium); undetermined for the pangolins
2. Trope Maker: Walking with Beasts (Leptictidium)

Near Ancient Shores: Mesonyx & Desmostylus *

Mesonyx ("middle-nail") was an Eocene North American mammal similar in size and shape to a strange dog or hyena with a big head and long tail, but with primitive hooves like Phenacodus or Eohippus. It was one of the first mammalian predators, but being no bigger than a modern dog, it was definitely not the apex predator in a world dominated by terrestrial crocodilians like Boverisuchus (formerly Pristichampsus) and huge flightless birds like Gastornis (which is now considered a herbivore). It was the namesake of a group of carnivorous basal ungulate-relatives called the mesonychians, who are most famous for having once thought to have been the ancestors of the cetaceans (the mysterious Andrewsarchus mentioned above was once considered part of this group).

The traditional image was that Mesonyx and is relatives roamed the coasts in search of dead fish and carcasses,, and that this was the kick-off of the evolution of whales. This could explain why the Walking With Beasts producers decided to show Andrewsarchus near the shore in search of turtles in its first relevant scene. Nowadays, whales are considered true artiodactyls descended from the same ancestor as hippos, while mesonychians are believed to be fully terrestrial predators that ruled the mammalian hunter niche in Asia, Europe, and North America during the Paleocene and Eocene before vanishing in the Early Oligocene.

Carnivorous ungulate-relatives are strange enough already, but few groups of extinct mammals have baffled scientists as much as the demostylians, the only totally extinct group of sea mammals ever. Debate rages over which modern mammal group this lineage of true sea mammals is most closely related to — they are traditionally believed to be afrotheres related to manatees and elephants, but the fact they are exclusively from the North Pacific contradicts the consistently African and Atlantic evolutionary history of the afrotheres, leading other scientists to propose they are instead perissodactyls or perissodactyl-relatives, closer to horses and rhinos. However, the jury remains out for now. Desmostylians looked a bit like hippos but with shorter hindlimbs than forelimbs and smaller heads. Also like hippos, they had small tusk-like incisors and canines, except these pointed forward and there were multiple on each jaw. They also possessed uniquely tubercled cheek teeth they used to eat kelp. They were once thought to be amphibious, but later studies suggest they were unable to support their weight on land and thus fully aquatic, mostly power-walking on the bottom like hippos do.

Desmostylus ("bundle-pillar", for the shape of its teeth) is the archetype and the most known of the group, first found by Marsh in USA during the Bone Wars; it lived in shallow coastal seas from Japan to Baja Califonia up to Alaska and Siberia during the Miocene. As a group, the demostylians lasted throughout the Oligocene and Miocene, going extinct as manatees and dugongs rose to prominence and entered the North Pacific (where they also eventually went extinct during historical times; see Historically-Extinct Mammals for that story). Interestingly, the demostylians are very popular in Japan, where they are among the most well-known groups of prehistoric mammals, due to the many fossils of them found there.

1. Entry Time: undetermined
2. Trope Maker: Popular books depicting sea mammals' evolution

When Whales were Spinosaurs: Pakicetus & Ambulocetus *

All mammals were small and rodent-shaped in their evolutionary beginnings. Some became larger and more derived after the extinction of the dinosaurs, but none to the same level as whales, who themselves are descended from even-toed ungulates.

The first cetaceans were likely freshwater/estuarine animals that lived on land but waded into water to feed on fish. Pakicetus ("Pakistan whale") is the traditionally most-portrayed of them. Found in Pakistan (duh) in 1981, it was still four-limbed and looked more like a wolf than whale (old illustrations depicting it as something akin to a mammalian crocodile were disproven with further fossil finds), but it had a long tail (the typical archaic trait of the earliest ungulates), anticipating the powerful muscular tail of later cetaceans. It was already a good swimmer, but probably swam using its legs like land mammals. Its nostrils were still placed at the tip of its snout like a land mammal, but its ears already showed specializations for hearing underwater like a modern whale. This combination of land and water adaptations makes Pakicetus another excellent example of a Mix-and-Match Critter.

First described in 1994, Ambulocetus (lit. "walking whale") was also found in Pakistan. It was larger and much more adapted for life in the water than the former, with shorter limbs, palmated feet instead of primitive hooves, and a more powerful tail. At the time of its discovery it was celebrated in media as the "missing link" between the still terrestrial-looking Pakicetus and more modern whales like Basilosaurus. Maybe because of this fame, Ambulocetus was chosen as the archetypical early whale in the first episode of Walking with Beasts, but was incorrectly shown in Europe instead of Asia and interacting with critters known from the Messel Pit like Leptictidium above. In the show, Ambulocetus was portrayed as an ambush-hunter of small land mammals, like a modern Nile crocodile; actually, its lifestyle is unknown. It may have been a specialist fish-hunter, like modern otters.

Both these early whale-ancestors had the same two tooth shapes in their jaws as Basilosaurus. But whereas Pakicetus was likely to have been a mostly-terrestrial animal that spent a lot of time in the water to hunt, Ambulocetus, once assumed to have been amphibious like a seal, seems to have been already fully aquatic, thus not really deserving the name "walking whale", but nomenclature rules being what they are, it's stuck with it. Both Pakicetus and Ambulocetus can be shown widely differently in paleo-art and paleo-books: sometimes they are portrayed hairy, sometimes naked-skinned like a modern whale. Apart of the lack of dorsal sail, they could be considered in anatomy the mammalian equivalents of the famous dinosaur Spinosaurus, though obviously both are much smaller than it.

1. Entry Time: End of the 20th century
2. Trope Maker: Documentary media about whale evolution

Moby Dick in Prehistory: Livyatan & the "Macroraptorial Sperm-Whales" *

A 2008 discovery made in Peru, Livyatan melvillei could make the much celebrated Basilosaurus quite insignificant in comparison. It possessed what may be the largest functional teeth of any animal ever at a little over a foot in length: that is, not counting tusks like on an elephant, walrus, or narwhal. The record for biggest teeth of all time is still held by giant extinct elephants like mammoths and Palaeoloxodon.

The size of the partly preserved skull indicates that Livyatan reached up to 57ft long, comparable to the modern sperm whale. The head was 3m long, only half that of a large male sperm whale and perhaps recalling in shape more the head of an orca. Livyatan was overall physically similar to the living sperm whale and belonged to the same group, Physeteroidea. Like all toothed whales, Livyatan had one single blowhole on its head, correspondent to the left nostril of the land mammals, and a fatty mass on its head (the "melon") to help echolocation — all specialized odontocetans traits, missing in the primitive whales like Basilosaurus, Ambulocetus, and Pakicetus, which had two symmetrical nostrils like all the other mammals. Livyatan had teeth in both of its jaws, in contrast to how sperm whales only have teeth in their lower jaw. It does however share this trait with Monstro, who is probably the best overall physical comparison, except Livyatan was smaller and lacked the rorqual-like underbelly ridges present in the Disney critter. By comparing its skull to that of a modern sperm whale, we know it would have had a spermaceti organ, the hallmark trait of the modern sperm-whales that gives them their name and sits above the melon to give them their iconic boxy heads.

Livyatan living during the Late Miocene, and the fossil beds it was found in have also produced Megalodon. It's also theorized that they had a similar taste in preferred prey: large marine mammals, such as baleen whales. Indeed, Livyatan hunted even more powerful prey than the modern giant squids eaten by sperm whales today, and it definitely would have had to directly compete with Megalodon for food. Perhaps Livyatan was even able to kill an adult Megalodon, like modern orcas do sometimes with the great whites. It also happens to be one of those prehistoric animals whose name is a reference, too. "Livyatan" is the Hebrew name for the Biblical sea monster Leviathan (note that the word of "whale" in modern Hebrew is just "livyatan"), and "melvillei" is coined after Herman Melville, the author of Moby-Dick.

Livyatan was not the only one of its kind. Throughout the Miocene lived similar sperm whale-relatives of smaller size and with smaller (but still huge) teeth: their scientific names recall the one of the modern sperm whale, Physeter macrocephalus, with a prefix ahead. Among the most notorious of these are the 15ft-long Acrophyseter from Middle Miocene Peru, the 23ft-long Brygmophyseter from Middle Miocene Japan (portrayed in Jurassic Fight Club as the rival of Megalodon), and the 23ft-long Zygophyseter from Late Miocene Italy; Acrophyseter and Zygophyseter stand out for having smaller spermaceti organs than the others, giving them a dolphin-like beak. Together with Livyatan are nicknamed "macroraptorial sperm whales" (not considered an actual taxonomic group within Physeteroidea). These animals were all apex predators that occupied the same niche as the modern orca; they certainly would have given Megalodon a run for its money as King of the Cenozoic Ocean!

1. Entry Time: The New '10s (Livyatan)
2. Trope Maker: Its size and power and its rivalry against Megalodon

Small Primate Relatives: Plesiadapis, Purgatorius, & Planetetherium *

Size doesn't always matter to make extinct mammals interesting to people. Plesiadapis was an archaic primate that lived in the Late Palaeocene and Early Eocene of North America and Europe. It was similar to a lemur but with gnawing teeth like a rodent (Mix-and-Match Critter again in play). Today, only one species of living lemur has gnawing incisors, the unrelated aye-aye of Madagascar.

Purgatorius, named after Purgatory Hill, was a small, more generic-looking shrew-like placental that lived in at both the very end of Cretaceous and the very start of the Paleocene, before and after the Great Dinosaur Extinction. As its fossils are known from the same sites that have produced the very last North American dinosaurs, it coexisted with the likes of Tyrannosaurus rex, Edmontosaurus, Ankylosaurus, and Triceratops, as well as the last pterosaurs like Quetzalcoatlus. But what makes this unremarkable-looking animal really stand out was that it is the earliest known primate! Related to the more derived Plesiadapis, it is often imagined similar to the modern treeshrew (a cousin of primates) in look — and so is frequently-mentioned in the sources talking about the evolution of humans together with Plesiadapis ("near-monkey").

Not primates but related to them are the colugos or "flying lemurs". Today found only in Southeast Asia, fossils show these animals were widespread in the past. Take for instance, Planetetherium, meaning "gliding beast". It lived in North America during the Late Palaeocene, and was very much like its modern counterparts (no skin impressions exist, but its body proportions match modern colugos, telling us it likely could glide). This mammal has also been frequently portrayed in prehistoric books and paleo-art, but not always linked with the evolution of humans — because of its flying-squirrel-like "wings", it was once once considered the possible ancestor of bats.

1. Entry Time: undetermined
2. Trope Maker: the discussion about human origins

Little Menace?: Didelphodon *

Didelphodon ("possum tooth") was, as its name suggests, related to marsupials — unlike the Ice Age Australian Thylacoleo, Procoptodon and Diprotodon, it was not a marsupial in the modern sense, as was once thought by scientists, but rather part of a basal family of marsupial-ancestors called Stagodontidae. Because of this, it's not known if Didelphodon had a pouch like kangaroos, or was pouchless like many opossums. Alongside Purgatorius, Didelphodon lived at the very end of the Cretaceous in North America, under the feet of T. rex and Triceratops. Unlike Purgatorius, it went extinct 66 mya with the dinosaurs. It was one of the bigger mammals of the Mesozoic at the size of an oppossum and formerly considered the biggest until the discovery of the badger-sized Repenomamus from Early Cretaceous China (a known predator of baby dinosaurs!).

Other mammals of the Mesozoic are the Early Jurassic Morganucodon and Megazostrodon (some of the earliest and most widespread), the beaver-like Castorocauda and gliding Volaticotherium of Middle Jurassic China, the Late Jurassic Juramaia and Early Cretaceous Eomaia of China (the earliest known placental-ancestors), the digging termite-eater Fruitafossor of Late Jurassic North America (living alongside Allosaurus, Diplodocus, and Stegosaurus), Cronopio of Late Cretaceous Argentina (a contemporary of Giganotosaurus that looked like Scrat from Ice Age), the platypus-like monotreme Stereopodon of Early Cretaceous Australia, the badger-sized herbivore of Adalatherium of Late Cretaceous Madagascar (depicted in Prehistoric Planet), the possum-like marsupial-relative Alphadon of Late Cretaceous Canada, the jerboa-like Zalambdalestes (which lived alongside Velociraptor in Late Cretaceous Mongolia), and the Late Cretaceous North American multituberculate Cimolodon (part of a group of herbivores that survived the Great Dino Extinction, only to be outcompeted by rodents in the Late Eocene). Phew!

Didelphodon used to be a very obscure animal, seldom portrayed even in prehistory books. But in 1999, it became abruptly famous when it was appeared in last Walking with Dinosaurs episode, “Death of a Dynasty”, as the annoying mammal stealing eggs from the mother T. rex. In the show, and science at the time, it was depicted as a badger-like creature, but fossil finds made after this revealed it resembled and behaved more like an otter, making the WWD portrayal very inaccurate now apart from its size.

1. Entry Time: 1999
2. Trope Maker: Walking with Dinosaurs

Historically-Extinct Mammals

Cattle Ancestor: the Aurochs **

This animal is not strictly prehistoric, but like the dodo, it went extinct in the Modern Era thanks to humans.

The aurochs (whose scientific name, Bos primigenius, means "primeval ox") was, together with the European bison (or wisent), the biggest European land mammal to survive the Ice Age and reach recorded history. It's a classic imprecision in media to say the aurochs was a prehistoric animal; this is not completely wrong, since it was widespread during the Ice Age both in Europe and Asia alongside woolly mammoths, woolly rhinos, cave bears and so on, but strictly "prehistoric" creatures are those that disappeared before the dawn of civilization (roughly 4000 B.C.).

Also known as the urus, the aurochs was a powerful animal, though sometimes oversized in media: it was actually no bigger than modern wild bovines. According to paintings, the aurochs' color varied from brown to blackish but usually darker than the wisent, its fur was quite long to withstand frigid winters but shorter than a yak's, and its body lacked the shoulder hump of a true bison. It roamed ancient forests and steppes, and was probably a browser/grazer like the wisent. Its predators would have included cave lions, cave hyenas, modern wolves, and brown bears, from which it defended itself with its long, robust, pointy horns and rapid charges — it was a fast runner despite its weight of one ton. It gave birth to one calf at a time after a long gestation of 10-11 months, and like all modern ruminants, it chewed its cud to better digest plant matter.

The aurochs was already known by prehistoric European people, the Neanderthals and the Cro-Magnons, who often depicted it in cave art — Lascaux in France and Altamira in Spain, for example — together with many other extinct and extant animals they hunted. Ancient Celtic, Greek, Roman and Medieval peoples too knew the animal, often mentioning it in literature as a particularly dangerous wild game, or as a symbol of power, or (in the case of the Celts) even as a divinity. Some peoples painted images of it on their war shields. The aurochs still appears in the national flag of the modern Republic of Moldova (in Europe).

But since Medieval and Renaissance times, the reduction of the forests/steppes it lived in, coupled with extensive hunting, made the aurochs rarer and rarer, until it disappeared entirely in the 17th century; the last individual died in 1627 of natural causes in Poland's Jaktorów Forest. The European bison managed to escape the same fate, only thanks to a bunch of individuals saved Just in Time in Białowieża between Poland and Belarus, in the 1800s.

The aurochs left an extremely crucial legacy in modern times, however: around the end of the Ice Age, 10,000 years ago, some aurochs (yes, not aurochses or aurochsen) were domesticated by humans. This domestication was one of the most successful and important ever: their descendants became the bulls, oxen, and cows (Bos taurus), whose contributions to mankind's development, as everyone knows, has been fundamental.

Interestingly, there are some very archaic cattle breeds that strongly resemble the aurochs, for example the famous Spanish Fighting Bull used in bullfighting. Some of these breeds have been reintroduced into ancient European forests (ex. Białowieża, the same place that saved the last European bison), resurrecting, at least partially, the memory of their wild ancestor's ancient presence.

1. Entry Time: European Antiquity
2. Trope Maker: Undetermined (maybe Pliny the Elder or Aristoteles, both naturalists)

Horse Ancestor: the Tarpan *

The tarpan was a true wild horse (Equus ferus: "ferus" = wild, "Equus" = horse in Latin) that lived in Europe until the Modern Age, but was depleted by humans. It was much more widespread during the Ice Age, with fossils also being found in Asia and North America (debate rages if the numerous North American Equus species represent individual variation in the tarpan or not). But by the Modern Age, the tarpan's range had been reduced to the steppes of Southern Europe — the last wild tarpans lived in southern Russia until 1879, and the last captive individual (also Russian) died in 1909. But also like the aurochs, the tarpan has left an important legacy in the form of its modern descendant, the domestic horse (Equus caballus). Some archaic domestic horse breeds even resemble the tarpan, and are visible in some European parks, just like cattle breeds that resemble their own wild ancestor.

The tarpan was a smallish, greyish horse very similar to the living conspecific Przewalski's horse and the equally rare wild asses of Asia and Africa: all of them combined a donkey-like mane with normal horsy tail. Its behavior was no different from modern wild equids, roaming grasslands and steppes in large herds to defend itself from predators. The tarpan too was depicted in prehistoric caves like the aurochs, and mentioned in classic European literature throughout the centuries as "the wild horse". Both the aurochs and the tarpan arguably shared the same voice (mooing and neighing respectively) as their domestic descendants, and both had a quite long gestation of 10-11 months, but the tarpan, being an odd-toed ungulate, didn't ruminate, like modern equines and unlike bovines.

1. Entry Time: European Antiquity
2. Trope Maker: Mentions in classic literature

Half Zebra: the Quagga *

All modern equines are so similar to each other in anatomy that they are all included in a single genus: Equus. This genus, as mentioned in the "horse ancestors" chapter, originated on the North American prairies, and then spread throughout Eurasia across Beringia, and later into Africa through the Sinai Peninsula. Modern "wild" (or rather, feral) horses of North America, Asia, Australia etc. actually descend from domestic horses returned to the wild — except for the Mongolian Przewalski's horse (Equus przewalskii), previously extinct in the wild but successfully reintroduced by zoos.

The quagga (Equus quagga) was an unusual-looking kind of zebra with dark & white stripes only in the front part of its body, and the remaining body colored uniformly brownish or whitish like many horses. It was closely related to the modern plains zebra (Equus burchelli), to the point they may even be the same species (in that case, the plains zebra would be renamed Equus quagga, as the quagga was described first). But unlike the latter, it lived only in the southernmost part of Africa — making it the southernmost kind of modern equine together with the Mountain Zebra (Equus zebra), which was formerly critically endangered until zoo reintroduction programs and wild conservation efforts saved it.

The quagga's lifestyle was probably identical or very similar to the surviving zebras, but sadly, it was overhunted by European settlers; the last wild individual died in 1878 and the last captive individual died in 1883. Being less skittish and more robust than other zebra species, the quagga was probably well-suited for domestication, making it all the more wasteful that it was instead hunted to extinction. Unfortunately, the quagga was not the only animal to fall to the overhunting of African colonialists — another notable extinction was the quagga's neighbor the Bluebuck (Hippotragus leucophaeus), a South African antelope related to the still-living sable antelope (Hippotragus niger).

The quagga is mentioned in the first Jurassic Park book as an example of a recently-extinct species of animal that could possibly be cloned in the park, and is still present in several tales from native South African peoples today. And speaking of Jurassic Park, it's actually one of several species being considered for De-Extinction programs to clone and resurrect recently-extinct animals, including the aurochs, the thylacine, the passenger pigeon, and most famously, the woolly mammoth.

1. Entry Time: Uncertain
2. Trope Maker: Embalmed mounts in natural history museums and animal books

Gentle Giant: the Steller's Sea Cow *

The story of this mammal is a particular Tear Jerker. The Steller's sea cow (Hydrodamalis gigas) was not a cow, despite the name, but a giant relative of modern manatees and dugongs — that is, a large sirenian, and not a cetacean at all, but a distant cousin of elephants.

9m/30ft long and weighing up to 10 tons, it was similar to a manatee in shape but with a smaller head and flippers, rougher hide, and the same whale-like fluke as a dugong, which it was more closely related to. It used to swim slowly and peacefully in the cold waters of the Northern Pacific coasts along with sea otters and sea lions, grazing kelp with its unusual toothless jaws (manatees and dugongs have few teeth). Like modern manatees and dugongs, it gave birth to one offspring at a time after a long gestation, and thus was not an especially fast breeder. The European explorers who encountered them described them as passive and slow-moving animals that floated on the surface (a result of their naturally buoyant bodies, unlike those of all other sirenians) and congregated in herds. Their sheer bulk, combined with their thick skin, kept Steller's sea cow safe from even orcas.

The common name of Steller's sea cow comes from German naturalist Georg Steller, the first European to describe the animals — he came across them on an expedition to the North Pacific under Russian explorer Vitus Bering when the crew got shipwrecked on the Commander Islands off the coast of Siberia in 1741. Steller (whose name is also on several other North Pacific animals, like Steller's sea eagle, Steller's sea lion, Steller's jay, and Steller's eider — all also first recorded by him) noted that sea cow was already rare at that time, with only few thousand individuals left — all of them only living around the Commander Islands. Unfortunately, hunters and whalers soon saw it as a great source of food and animal grease because of its size, and also noted that it was a relatively easy animal to kill, more so than the bigger and/or faster cetaceans nearby. The result was: the giant sirenian went extinct merely 27 years after its discovery in 1768 — most other historically-extinct mammals and birds were depleted at least one century after Western people learned about them. Sadly, fossil evidence indicates Steller's sea cow was much more widespread during the Ice Age and into pre-Modern History, ranging from Japan to Alaska down to Baja California, until humans too exterminated them from overhunting — it's likely the ones Steller encountered were the very last of their kind.

Steller's sea cow has made a few notable appearances in pop-culture, to date. Rudyard Kipling featured it prominently in his story The White Seal, published as part of The Jungle Book, where one of the last surviving individuals is sought for advice by the title character. Also, the 2012 docufiction Tales of a Sea Cow involved the 2006 discovery of a a surviving population of Steller's sea cows off the coast of Greenland as its premise — indeed, Steller's sea cow is occasionally sighted today, making it something of a cryptid now. However, it is not the sole historically-extinct marine mammal: the Yangtze river dolphin or baiji, was declared extinct in 2006, while the Caribbean monk seal suffered the same fate in 1952.

1. Entry Time: 1894
2. Trope Maker: The Jungle Book

Extinct or Not?: the Thylacine **

This mammal is not strictly prehistoric, to the point that it could actually still be alive today. Nonetheless, like the animals above, it has left several fossils from prehistoric times.

In popular media, the thylacine (Thylacinus cynocephalus, lit. "pouched dog with a dog head") is known as the Tasmanian wolf or the Tasmanian tiger. Wolf, because its shape and size effectively recall that of a long-tailed, round-eared wolf — to the point that it's often cited as an example of convergent evolution with true canids. Tiger, because of its coloration, which was vaguely similar to the eponymous cat but with a simpler design: wide black stripes on the rear of its back upon an otherwise uniformly brownish body.

But this mammal was neither a canine, nor a feline; it was a marsupial, just like kangaroos! More precisely, it was not part of the Diprotodontia order like them, but rather a member of Dasyuromorphia, which contains all of the modern carnivorous marsupials of Australia, like the Tasmanian devil, the quoll, and the numbat (remember, Thylacoleo was in Diprotodontia; its closest living relatives are wombats and koalas). It's called Tasmanian because Europeans found it only on the island of Tasmania, but in the past, the thylacine also lived on mainland Australia — until it was outcompeted by the dingo when the latter was brought in the Land Down Under by the ancestors of Aborigines thousands of years ago (the still-living Tasmanian devil suffered the same fate). During the Ice Age however, it would have not been the apex predator of the continent, what with the giant lizards, marsupial lions, and terrestrial crocodiles romping around.

Like all the other historically-extinct birds and mammals detailed on these pages, the thylacine is often and rightly mentioned as an example of human irresponsibility. Its possible extinction happened only in the 20th century: old black-and-white films exist showing the animal alive in zoos, and reveal that it could open its mouth rather widely for a mammal. It was hunted to extinction mainly because Tasmanian farmers of the 19th and 20th centuries considered it a serious peril to their livestock, especially their sheep and their poultry. This was only partly true, however, because the animal mainly hunted wild game. The alleged ferocity of the thylacine was notably exaggerated by several reportages and citations in books and encyclopedias as well. These accusations of viciousness and perilousness, even toward humans, were among the excuses that led to it and its placental namesakes, the grey wolf (Canis lupus) and the tiger (Panthera tigris) being driven to endangerment or extinction in many countries worldwide. The last known wild thylacine was killed in 1930, while the last captive thylacine died at Hobart Zoo in Tasmania on September 7, 1936 (now commemorated in Australia as National Threatened Species Day).

Despite being extinct, the thylacine has entered pop-culture as one of the icons of Australian wildlife, with appearances in video games, cartoons, movies and literature. A boomerang-wielding thylacine is the protagonist of Ty the Tasmanian Tiger, while Tiny Tiger is a recurring villain in the Crash Bandicoot. The competitive shooter game Valorant and young adult novel Leviathan both feature thylacines being kept as pets by a major character, while the cartoon Tazmania has a neurotic thylacine named Wendell T. Wolf co-starring with Taz of Looney Tunes fame. The thylacine also appears on Tasmania's coat of arms and numerous other Tasmanian logos; it also regularly appears in the stories of the Australian Aboriginals. Most interestingly however, alleged sightings of surviving thylacines have become a regular thing since its official extinction in 1936, making it something of a cryptid too. While regularly reported in newspapers in the form of stories about "the last thylacine", none of them are confirmed — at least for now.

1. Entry Time: Undetermined
2. Trope Maker: Uncertain, possibly footage and photos of zoo specimens

Other extinct mammals

Sorry, these aren't here. If you're looking for Protosiren, Titanohyrax, Teleoceras, Metamynodon, Homotherium, Borophagus, Cynodictis, Viverravus, Pelorovis, Titanotylopus, Protoceras, Prolibytherium, Remingtonocetus, Eurhinodelphis, Merycoidodon, Anoplotherium, Thalassocnus, Stegotherium, Palaeolagus, Palaeocastor, Phoberomys, Icaronycteris, Dinopithecus, Archaeoindris, Phascolonus, Palorchestes, Murrayglossus, and others, see here.

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Prehistoric Amphibians

Extinct amphibians are interesting, and the ones listed below are all from before the dinosaurs (though, of course, authors frequently forget that and put them in dinosaur settings anyway).

Amphibians in Media

The First Vertebrate with Limbs?: Ichthyostega **

Although not a amphibian in the technical sense of the term, Ichthyostega has always been one of the most iconic paleo-amphibians. Found in Greenland — Hilarious in Hindsight, during most of prehistory, Greenland really was a green land, covered with forests; the ice cap formed only 30 million years ago in the Cenozoic — Ichthyostega lived before all the animals mentioned above, in the Late Devonian, about 360 mya, in a time when flying insects didn't yet exist and the very first forests had just started to grow.

Described in 1932, it was long considered among the very first land vertebrates and the common ancestor of all tetrapods (mammals + birds + reptiles + amphibians). Like Archaeopteryx, Ichthyostega has been often cited as a "missing link" between two main animal classes: fish and amphibians in this case, and like the "ur-bird", it is seen as an icon of evolution. However, older intermediate forms between fish and land animals have been found since; the 365 mya-old Acanthostega (found in Greenland in 1952) and the 375 mya-old Tiktaalik (2006 in the Canadian Arctic) are some relatively known examples.

Like many other basal tetrapods (properly known as stegocephalians), Ichthyostega was a big animal, 5ft/1.5m long and weighing as much as an adult human. This half-fish/half-amphibian, often quoted as a "fish with legs" or an "amphibian with fins", was indeed one of the first animals that developed true legs, already similar to modern animals except for one thing: it had seven digits on each foot — later vertebrates have no more than five, except for very rare anomalies like some ichthyosaurs. Its body plan, however, had still several fishy traits (Ichthyostega indeed means "roof fish"): a streamlined body, fish-like scales, a powerful tail with a long true fin on top, and maybe even a "lateral line" to sense underwater! On the other hand, it could have had eyelids and external ears like in modern amphibians, as well as two breathing lungs in the adults. The larval stage is unknown, but it was certainly made of "tadpole"-like gilled small creatures that hatched in water and then underwent a metamorphosis like in modern amphibians, but also like in modern lungfish.

But wait! Though classical portrayals show it crawling on dry land, today scientists think Ichthyostega lived mainly in water, and recently research suggest its limbs were not used for walking on dry soil but only on the bottom of lakes and rivers, like a modern giant salamander (the biggest living amphibians today, incidentally the same size of Ichthyostega).

In Walking with Monsters, its close and almost-identical (but slightly older) relative Hynerpeton, found only in 1994 in Pennsylvania, is shown in the traditional mainly-terrestrial way, but also with many unlikely traits typical of modern true amphibians: like frogs, it's given a loud voice and scale-less skin, and lays eggs that are just the same shape as frogspawn. One individual is killed and eaten by the giant lungfish-like Hyneria (see Eusthenopteron in the next folder below for more on that).

1. Entry Time: Unknown
2. Trope Maker: Educational media

The Hammerhead Salamander: Diplocaulus *

Diplocaulus was 1 meter long, smaller than Ichthyostega (but still bigger than most modern salamanders) and lived in Early Permian North America contemporary with the famous predatory proto-mammal Dimetrodon. Its unique boomerang-like head makes it a very bizarre-looking and enigmatic prehistoric animal, and a very common sight in paleo-books (though it has not yet appeared in CGI documentaries). The purpose of its head protrusions has been a headache to paleontologists: A swimming device? A display tool? A mean to excavate the bottom of lakes? An attachment point for gills? A defense mechanism? Some have even proposed that it supported skin flaps that made the animal look like a stingray when alive.

Diplocaulus means "double-stem" — while Diplodocus means "double-beam". It was a true amphibian, but not a member of the group comprising modern amphibians (the lissamphibians): it was the largest of the lepospondyls, a Carboniferous-Permian group whose shape only coincidentally recalled that of modern salamanders and newts. Its eyes and nostrils were placed on the top of its flattened head, and were very close to each other (the exact opposite of a modern hammerhead shark, whose eyes and nostrils are at the extremities of the "hammer"), which gave it what may have been a rather funny appearance if seen from above.

According to experts it was mainly aquatic, probably swimming with its tail and/or walking on the bottom of the water with its five-toed feet. Diplocaulus likely fed upon small water critters, and would have fallen prey to larger amphibians and Dimetrodon. One remarkable discovery was of a burrow of eight Diplocaulus with three individuals having bite marks on their heads from a Dimetrodon that unearthed them, likely as they were hibernating during a drought as many modern amphibians do. It was likely quite clumsy when on land, being arguably as slow as a big modern salamander on dry soil. In water, on the other hand, it could have been more fast and agile. We don't know what shape its larvae were, since it belonged to a totally extinct group of amphibians. It also could have had a lateral line like fish do to hear vibrations underwater, as some modern lissamphibians that live in water do have it.

1. Entry Time: Unknown
2. Trope Maker: Its skull

The Alligator Frog: Eryops *

Temnospondyls (lit. "cut vertebrae") were the most successful group of true amphibians in Real Life, thriving from the Late Carboniferous to the Late Triassic, with one holdout reaching the Early Cretaceous. Many of them looked like salamanders mixed with crocodiles, and the most iconic of them has traditionally been Eryops megacephalus ("big-headed drawn-out face").

2.4m/8ft long, bigger than Ichthyostega, and weighing as much as two adult humans, Eryops was the size of a small crocodile, and has indeed classically been compared with crocs in documentary media. But Eryops was more massively-built than a modern-day crocodilian; it had a shorter tail, lacked armor, and had comparatively weaker legs, making it probably more awkward than a croc on land. Still, it had a massive, very alligator-like head, with eyes placed above the skull and a large snout. Its teeth were different from those of a gator, though, being thinner and more numerous, more like a gharial's.

Living in Early Permian North America, Eryops is believed by most experts to have been mainly aquatic — other temnospondyls from its time and place, such as the equally short-named armored Cacops and the sail-backed 'Platyhystrix, were more terrestrial. Eryops was likely a predator of other smaller amphibians such as Diplocaulus above, as well as fish and invertebrates, but when on dry land, it could have fallen prey to Dimetrodon. Nonetheless, it can't be ruled out that it could have eaten baby Dimetrodon and Edaphosaurus if it got the chance. Like Diplocaulus and modern amphibians, it would have laid its eggs in the water, but its tadpoles would have just looked like tiny versions of the adults (we have fossils of temnospondyl tadpoles proving this). Like many other extinct amphibians, Eryops can be wrongly portrayed with reptilian scales and reptilian nails in illustrations, making it look more like a reptile than an amphibian.

1. Entry Time: Unknown
2. Trope Maker: Educational media

The Biggest Amphibian Ever?: Mastodonsaurus *

From the Middle Triassic comes the even larger Mastodonsaurus. Its name means "mastodon lizard" for its size, and sometimes is misspelled "Mastodontosaurus". It was the very first temnospondyl discovered by science, in 1828, and was portrayed in the London Crystal Palace Park as "Labyrinthodon" (although depicted as literal giant toads with gator-like heads; only the skull was known at the time). It was the namesake of the "labyrinthodonts" ("labyrinth teeth"), an informal name for all temnospondyls, basal tetrapods, and reptiliomorphs (see below) — so-named because many had teeth with strange convoluted "labyrinthic" patterns of enamel inside them for uncertain purposes.

Mastodonsaurus lived in Europe before the first dinosaurs like Plateosaurus or the North American Coelophysis. 15ft/5m long, it was long considered the biggest amphibian ever, but this title was later taken by the 8m long but more slender Prionosuchus of Early Permian Brazil. Nonetheless, Mastodonsaurus remains remarkable for its massive body, powerful limbs, and its 1.2m/4ft-long head with a couple of strange protruding teeth in the lower jaw, which may have perforated the upper jaw in life (though this latest detail is usually ignored in paleo-books).

Temnospondyls first appeared in the Early Carboniferous, and proceeded to dominate the world's waterways from the Late Carboniferous to the Early Triassic, occupying the same niche held by crocodiles today. Some became more land-dwelling (although still bound by the need to lay their eggs in water), and others even managed to enter the ocean (all living amphibians are all freshwater-bound or terrestrial and cannot survive in saltwater). But in the Middle and Late Triassic, they entered a sharp decline as they were outcompeted the ancestors of crocodilians. The last species, Koolasuchus of Walking with Dinosaurs fame, managed to reach the Early Cretaceous only because of its isolation in Australia, which at the time was in the Antarctic circle and thus too cold for crocs. However, it seems the temnospondyls may not be as extinct as we thought, as new research suggests the modern-day lissamphibians (frogs, toads, newts, salamanders, etc.) may in fact be the sole surviving descendants of these giants.

1. Entry Time: 1854
2. Trope Maker: The Crystal Palace Park in London

Nearly Reptile: Seymouria *

Reptiliomorphs ("reptile-shaped") were transitional animals between amphibians and the first amniotes (reptiles, birds and mammals). We don't know if they already had scaly skin like reptiles, or were naked like amphibians today. Traditionally, the best-known among these half-amphibian/half-reptiles has been Seymouria baylorensis. The genus name comes from the town of Seymour, Texas, near where it was discovered; the species name from Baylor County (where Seymour is in).

Seymouria used to be described in textbooks as the "missing link" between reptiles and amphibians, or alternatively the very first reptile. Only 60cm long, like Diplocaulus, it lived in Early Permian North America alongside the "hammerhead salamander" and Eryops. It was more terrestrial than them though and was possibly a regular prey item for Dimetrodon in Real Life. In Walking with Monsters, however, it's shown (albeit unnamed) mainly as a potential thief of the latter's eggs. Despite its similarity to reptiles, Seymouria still laid shell-less eggs from which "tadpoles" hatched in water, as some fossils show (although said tadpoles looked just like tiny versions of the adults).

Prehistoric true frogs are rarely-seen in Fictionland, but when they do, they normally don't belong to specific kinds of frogs or toads; for example, the "tailed frog" that jumps near Littlefoot in The Land Before Time film is an invention of the movie, though ancestral frogs really existed at dinosaurs' time, some very similar to the modern ones.

1. Entry Time: Unknown
2. Trope Maker: Educational media

Other prehistoric amphibians

Sorry, these aren't here. If you're looking for Triadobatrachus, Karaurus, Eocaecilia, Beelzebufo, Phlegetontia, Platyhystrix, Cacops, Branchiosaurus, Gerrothorax, Metoposaurus, Eogyrinus, Westlothiana, Diadectes, and others, see here.

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Prehistoric Fish

It's not often that you'll see prehistoric fish in paleo-media, but when you do, it will usually be these guys. The first two are the most common, especially the one at the top of the list.

Fish in Media

Jaws on Steroids: Megalodon ***

It's usually accepted that the biggest/most spectacular prehistoric animals lived in the Age of Reptiles, the mythical Mesozoic. Well, sharks give us a notable exception in Megalodon. This is the biggest predatory shark ever, and it lived just a few million years ago, at the time of the first hominids!

Obviously, this animal is often shown in documentary media: for example, its open jaws are often depicted with some people inside to show how immense they are. However, this animal has also begun to fascinate the world of fiction, most notably in the book Meg and its movie adaptation The Meg. But wait: Megalodon (literally "big tooth") is not the name of its genus; it's that of its species. The full scientific name used to be Carcharodon megalodon; today it's Otodus megalodon (or Carcharocles megalodon, depending on who you ask). It was once believed to be an extremely close relative of the great white shark (Carcharodon carcharias) in the family Lamnidae, but today, it's placed in Otodontidae, a different family convergently similar to the great white's. However, both Otodontidae and Lamnidae are in the same order of sharks: the Lamniformes, which also include the thresher shark, basking shark, megamouth shark, goblin shark, and sandtiger shark, among the others.

Like the most impressive extinct beasts, Megalodon is often a victim of sensationalism. Some sources describe it as 30m/90ft long, nearly as big as a blue whale; palaeontologists estimate it at just over a third to just under two thirds of this length. Still, it remains one of the biggest known fishes of all time, as well as the biggest known predatory shark, and one of the most successful apex predators ever, with a tenure of 20 million years, lasting from the Early Miocene to the Early Pliocene and being found worldwide.

Megalodon was a specialist hunter of large cetaceans, and its bite marks have been found on whale skeletons, but it also could have fed on smaller prey. We don't know what colors it was, but it was arguably countershaded, like typical big swimming sea creatures (such as great white sharks). If it was solitary or lived in groups is uncertain. It probably gave live birth, like all lamniform sharks do, and it left its young to grow in warm shallow-water coastal "nurseries" as great whites do (baby megalodons are estimated to be about 3.5m/11ft long). As typical of prehistoric sharks, its most common fossil remains are jaws and teeth, not the softer cartilaginous rest of its skeleton, which rarely fossilizes.

We don't know why it went extinct, but the most popular theory is that climatic changes deprived it of its main food sources: in particular, the formation of the Isthmus of Panama, would have closed off an important hunting, breeding, and migration area and caused major shifts in the world's currents and weather systems. It is hypothesized that Megalodon held back the evolution of cetaceans themselves, which underwent a third explosion in diversity right after its extinction — therefore, the theory that orcas outcompeted the giant shark is highly unlikely.

Megalodon is probably the one prehistoric creature that gets almost as much sensationalism as Tyrannosaurus rex. From frequent, fraudulent reports of it still patrolling the seas to erroneous portrayals of it chomping on Mesozoic marine reptiles (despite not appearing until long after those creatures had gone extinct), Megalodon is frequently cast as the ultimate sea predator. This obviously cannot be verified — in the Walking with… spinoff Sea Monsters it's portrayed as "only" the third-most-dangerous marine superpredator of prehistory, after the sea reptiles Tylosaurus and Liopleurodon, but before the fish below.

1. Entry Time: Late 1990s/early 2000s (pop culture)
2. Trope Maker: Documentary books on the shark buff side, Meg in pop culture

Living-Tank Fish: Dunkleosteus **

The placoderms were a group of armored fishes that thrived during the Devonian period, going extinct at its end, well before the dinosaurs evolved. Most were small, obscure animals, but the big exception is the most infamous of them all — Dunkleosteus ("Dunkle's bone"; formerly known as Dinichthys, "terrible fish").

Size estimates for Dunkleosteus have varied across the decades between 4-10m/13-33ft in length, but either way, it would have been one of the biggest members of its group. A lot of the difficulty in determining its size is because Dunkleosteus is only known from its skull, as placoderms, like sharks, have cartilage skeletons that don't usually fossilize. Traditionally depicted with an eel-like body due to comparisons with its smaller and lesser-known (but better-preserved) relative Coccosteus, the modern vision of Dunkleosteus gives it a more shark-like tail, complete with a dorsal fin. Its most distinctive and notorious feature however is its armored head, equipped with strange scissor-like "teeth" that were in fact plates of sharpened bone that were only further sharpened by simply being gnashed together.

It was evidently the top predator of its time: the Late Devonian, the same period in which the ur-"amphibian" Ichthyostega lived, and its fossils have been found in North America, Europe, and Africa. Studies of its jaw reveal that it probably sucked up food like a vacuum as many modern fish do, using its tooth-plates to slice through armored prey in less than a second, like a giant guillotine. Since it couldn't chew, it would have had to regularly regurgitate the armor and bones of its prey in the same way owls regurgitate pellets of undigestable bones and fur; indeed, its fossilized vomit is regularly found in Late Devonian fossil beds. Additionally, several Dunkleosteus fossils preserve evidence of being attacked by other Dunkleosteus, which has led some to suggest that they were active cannibals like many fish today are. It was traditionally thought of a slow creature due to the way it was formerly reconstructed, but we now believe it was a very fast-moving animal that pursued early sharks, ammonites, and other placoderms in the open ocean. Since placoderms are totall extinct, we cannot easily compare Dunkleosteus with modern fish, but based on on some exquisite specimens of smaller placoderms, it likely gave live birth.

Despite its status as "the living tank fish", Dunkleosteus has not gained much attention outside of paleo-books. Its most prominent appearance to date is Sea Monsters, where it's ranked as the fifth-most-dangerous ocean superpredator of all time, after two marine reptiles, Megalodon, and the early whale Basilosaurus. This version of Dunkleosteus has its scare-factor amped up to emphasize the "sea monster" image, with cat-like eyes and blood-red coloration, whereas most other portrayals show it with round pupils like a typical fish, and more generic colors.

1. Entry Time: Unknown
2. Trope Maker: Documentary media

Overgrown Herring: Xiphactinus *

The marine reptiles were not the only large ocean predators of the Mesozoic. Asides from sharks, one of the most infamous was Xiphactinus audax, which roamed Late Cretaceous oceans worldwide (with most fossils being found in North America). At 5–6m/16–20ft, this bony fish is longer than most great white sharks and rivals a small orca in length. Among bony fish alive today, the only ones of comparable size are the most massive — large sturgeons and the ocean sunfish (or mola mola). It wasn't the biggest bony fish ever though: that honor goes to the Late Jurassic filter-feeder Leedsichthys, known mainly from Europe and estimated to be over 50 feet long.

Xiphactinus goes by a lot of names — informal works often nickname it the "bulldog fish" or the "X-fish", but it also used to be known as "Portheus molossus". Xiphactinus audax means "courageous sword ray"; the meaning of "Portheus" comes from a Greek mythical character, but "molossus" refers to an early breed of mastiff. Indeed, its protruding lower jaw slightly resembles that of a bulldog; this, together with its long-pointed teeth, clearly indicates it was a predator. Like most modern bony fish, it swallowed and sucked its prey whole — some of which were nearly half its size! Its behavior in life could have been comparable to modern species of large, fast-moving predatory fish, like tuna — actively pursuing prey, but it's uncertain if it lived in shoals or was solitary. Like large modern bony fish, it arguably had external fertilization and lied a huge number of tiny unshelled eggs (sharks have internal fertilization, their eggs have a keratinous "shell" and are bigger and less numerous). Xiphactinus belonged to a Mesozoic-exclusive group of bony fish called the ichthyodectiforms, most of which superficially resembled tarpons and lived very similar lifestyles to Xiphactinus.

Xiphactinus has appeared in quite a few documentary media, most notably Sea Monsters and Prehistoric Planet. Both series depict the fish hunting and feeding on the mans-sized swimming bird Hesperornis, with the former show also having it fall victim in turn to the dominant marine reptiles of the Cretaceous (especially large mosasaurs like Tylosaurus). Despite its reputation as a voracious predator, it's largely ignored in mainstream media, likely because prehistoric bony fish have a pretty "generic fish" look when compared with the other giant sea-dwellers of the past, like marine reptiles, cetaceans, giant sharks, cephalopods, etc.

1. Entry Time: Uncertain
2. Trope Maker: Educational media

Fish Conquer the Land: Eusthenopteron *

First described in 1881 from fossils found in Canada, this early relative of lungfish and the coelacanth is classically mentioned in paleo-books coupled with Ichthyostega to show how vertebrates came onto land for the first time. Living in the Late Devonian about 385 mya, the long-named Eusthenopteron means "good strong fin". Its shape recalled a bit that of the famous ur-"amphibian" above, but smaller (60cm), with fleshy paired fins instead of true legs, classically fishy dorsal and anal fins, and a curious three-lobed caudal fin reminiscent of Poseidon's trident. It even had labyrinthic teeth, underlining its affinity with the first tetrapods and extinct amphibians. It's frequently depicted in paleoart as being able to breathe air and crawl out of the water like a lungfish, but newer research suggests it was a strictly aquatic animal — the more derived Panderichthys that lived about 5 million years later in Latvia (discovered 1941) was able to do the above. Like lungfish, its fry very probably underwent metamorphosis, but unlike them, the adults were scaly like a coelacanth).

Its almost-identical relative Hyneria was much bigger (3-4m long), and because of its size was chosen by Walking with Monsters producers instead of the better-known Eusthenopteron as the representative of its group. However, it's shown only to provide a predator to the Ichthyostega relative Hynerpeton, and with no mention at all of its role as one of the forerunners of land vertebrates (despite even showing it crawling onto land to pursue Hynerpeton, which it likely was not able to in real life, given what we now know): in effect, it was eating its descendant!

1. Entry Time: Uncertain
2. Trope Maker: Educational media

Fish or Shellfish?: Cephalaspis & Pteraspis *

Cephalaspis and Pteraspis are perhaps the two most-depicted members of the ostracoderms in paleo-media — at least, non-fictional media. The ostracoderms were an informal (non-scientific) grouping of armored fish that looked a bit like tiny bony fish at a glance — that is if today's minnows and guppies wore crash helmets. In actuality, their closest living relatives are lampreys and hagfish, and likewise, they lacked jaws. This last trait differentiates them from the also-armored placoderms, which were among the first jawed vertebrates.

Cephalaspis ("head shield") and Pteraspis ("wing shield") both lived during the Early Devonian, with their fossils being extremely numerous and widespread. These were totally harmless creatures — Pteraspis was only about 20 cm long, while Cephalaspis was about as big as a trout. And whereas their modern cousins, the lampreys and hagfish, are parasites and scavengers, these were inoffensive filter-feeders, with Cephalaspis using its flat, shovel-shaped head to sift through muck and Pteraspis swiftly swimming in the water column with ease, thanks to its narrow and pointy head.

Cephalaspis and Pteraspis are the namesakes of two major groups of ostracoderms, Cephalaspidomorphi and Pteraspidomorphi. Ostracoderms thrived in the Early Paleozoic, first appearing in the Ordovician and going extinct at the end of the Devonian. Cephalaspis appears in Walking with Monsters as the protagonist, of the Silurian segment, escaping the claws of giant "scorpions" and migrating into freshwater to spawn like salmon — the last behavior is entirely speculative, no to mention highly unlikely, given that Cephalaspis was a slow swimmer compared with most modern fish.

1. Entry Time: Uncertain
2. Trope Maker: Educational media

Other prehistoric fish

Sorry, these aren't here. If you're looking for Coelacanthus, Mawsonia, Dipterus, Palaeoniscum, Hybodus, Stethacanthus, Helicoprion, Climatius, Bothriolepis, Coccosteus, Arandaspis, Drepanaspis, Birkenia, Haikouichthys, the Conodonts, and others, see here.

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Prehistoric Invertebrates

It's uncommon to see prehistoric invertebrates in Fictionland, but some are so common in ancient rocks (even cropping up in fossil markets and shops, as well as popular paleo-books and magazines) that they've become familiar to the public nonetheless.

Invertebrates in Media

The First successful Invertebrates: the Trilobites ***

Some things have had more impact than others. Trilobites are among them. Their extreme abundance in the fossil record had made them index fossils: that is, Paleozoic rocks can be easily recognized just because they almost certainly contain at least one trilobite.

As a group, trilobites lived through the whole Paleozoic era, but became rarer and rarer after the Devonian, and none survived the devastating Permian mass extinction: thus, they might be taken as the Paleozoic's unofficial symbol. Trilobites were arthropods, and though their appearance could lead to them being confused with woodlice or horseshoe crabs, they were closely not related to any modern arthropod groups.

"Trilobite" means "three lobes". Their bodies were divided into three parts: the head, the segmented thorax, and the telson (the scute at the rear end of the body). But their flattened bodies also show three parts in the longitudinal sense, the middle segment and the two lateral ones (like this). They had many pairs of legs (up to 100), one pair of antennae, many pairs of gills, and two, usually large, compound eyes similar to those of insects; trilobites were among the first creatures capable of seeing images. They fulfilled many ecological niches: some lived on the bottom, some were active swimmers, some were scavengers, some were predators, some ate plankton, and some even crawled onto land. There's even speculation that parasitic trilobites existed! They also came in a variety of sizes, ranging from being shorter than a human finger to 3ft/90cm long. Some were equipped with unusual features and defenses, including horns, spikes, and eyestalks; a few were even able to curl up for protection, like pillbug woodlice do. Baby trilobites were identical to the adults, and like modern crustaceans, they shed their exoskeletons to grow. Of the 10 orders of trilobites known to science, the most frequently presented in media are the phacopids, which are probably what usually appear in your head when you think "trilobite".

In fiction, trilobites can often be seen in underwater visuals, usually as ambient animals that skitter about on the ocean floor. They might even show up in the Mesozoic alongside dinosaurs, despite having actually gone extinct millions of years before the first dinosaurs. They're much more common in older works, where they tend to be used as an indicator of "prehistoric" — for example, in the original Godzilla (1954), a living trilobite is found in one of Godzilla's footprints, indicating his origins to the characters.

1. Entry Time: Unknown
2. Trope Maker: Educational media.

The Symbol of the Mesozoic: the Ammonites ***

Is there anyone who hasn't seen those spiral stony shells emerging from the surrounding rocks? Ammonites, more technically ammonoids, have always been among the most iconic fossil invertebrates, together with the trilobites. They originated in the Paleozoic during the Early Devonian, only reaching their prime in the Dinosaur Age. They went extinct at the end of the Cretaceous alongside the nonbird dinosaurs, marine reptiles, and pterosaurs, when the asteroid struck. Ammonites are cephalopods, related to octopuses and squids — although it resembles an ammonite, the modern nautilus is not descended from them, being part of an older group of shelled cephalopods called the nautiloids (we'll get to them later).

Despite the abundance of their shells, their soft bodies are only rarely preserved and poorly known. They had ten tentacles, a beak, a small siphon for jet propulsion, and even an ink sac. Given that they were more closely related to octopuses and squids than to nautiluses, it's likely that their tentacles had suckers and that they had complex eyes to see images (nautiluses lack either trait). Many were excellent swimmers, but others were slow-moving bottom-dwellers. Their diets likely varied from species to species, with some being active hunters and others being filter feeders. Their hard shells were excellent protection against predators, as shown by some ammonites with marks of teeth left by ichthyosaurs or mosasaurs which tried to break the shell in vain. Like nautiluses, their shells also let them function like miniature submarines, with small chambers they could fill with water or empty to control bouyancy and depth. Ammonites laid their eggs in coastal shallows and produced planktonic larvae, which made them extremely vulnerable to the devastating effects of the asteroid that ended the Cretaceous — unlike nautiluses, which lay their eggs on the deeper seafloor and have babies that look just like tiny adults. Most ammonites were no bigger than a human hand, but some were as big as tractor tires. Many ammonite genera end with -ites, ex. Ceratites, Goniatites, and so on, while many others end in -ceras: Dactylioceras is one.

In media, ammonites are always shown with the classic curly, laterally-flattened shell; these are known as homomorph ammonites. During the Cretaceous however, some ammonites showed unusual forms; these are called hetereomorph ammonites, all within the group Ancyloceratina. Some had loosely uncoiled shells, some had u-shaped shells, some had spiny tower-like shells, some just had straight shells, and others had shapes so bizarre they must be seen to be believed. Prehistoric Planets second season shows off a small handful of these, but this Japanese artist gives us even more! No one is certain how these ammonites lived; none were likely to have been fast animals, and they may have been either bottom-dwellers, jellyfish-like free-floaters, or mostly stationary animals.

Ammonites, like trilobites, are common as ambient animals in paleo-media, though their presence in Mesozoic works at least makes more sense seeing as they were extremely common back then and their fossils are among the most commonly found. So common, in fact, that like the Paleozoic trilobites, individual ammonite species are used as "index fossils" for the Mesozoic, with their presence in layers of rock denoting specific geological time zones.

1. Entry Time: Unknown
2. Trope Maker: Educational media.

The First Giant Flyer: Meganeura **

Popularly referred to as a "giant dragonfly", Meganeura ("big nerve", a reference to its heavily-veined wings) was in fact a part of a related group of insects, Meganisoptera (formerly called Protodonata), informally known as "griffinflies". Actual dragonflies and damselflies belong to the group Odonata, and while Meganeura was extremely similar to them, its lineage has been extinct for over 250 million years.

Meganeura's most iconic quality was its size. With a wingspan like a crow (not like an eagle as is sometimes said), Meganeura has been called the largest-known true insect of all time (millipedes like Arthropleura are not insects), although in reality, it had some larger relatives, such as Meganeuropsis. As stated above, Meganeura had the same shape as modern dragonflies, with a slender body, huge eyes with excellent vision, short antennae, powerful mandibles, and two pairs of independent-moving wings; it would have likely been a very powerful flyer, perhaps as fast as many modern birds.

Meganeura lived in the swamp-forests of Late Carboniferous Europe alongside the giant millipede Arthropleura (below), while its bigger cousin Meganeuropsis lived in the Early Permian of North America — this still makes Meganeura the earliest known Giant Flyer. Unlike Arthropleura, Meganeura was carnivorous and fed on smaller insects, catching them with spiny legs (like dragonflies) and tearing into their flesh with large mandibles (unlike dragonflies, which have much smaller, less visible mouthparts). Meganeura and Arthropleura were usually safe from the predators of the time: the millipede's armor and the griffinfly's agility protected them against giant amphibians and large fish. Fossils of Meganeura nymphs are known too, and like modern dragonfly nymphs, they were fierce aquatic predators.

In media, Meganeura is more common than its land-bound neighbor Arthropleura. Like trilobites and ammonites, Meganeura tends to be an ambient animal in fiction, that exists mostly to emphasize a prehistoric setting. Older works tend to portray Meganeura as living alongside dinosaurs, despite the fact that it had already died out long before the dinosaurs arrived on the scene. A good example is in the first Jurassic Park novel, where a cloned Meganeura is present in the park. This is despite the fact Meganeura went gone extinct long before mosquitoes or even amber would have existed — mosquitoes and modern conifer trees appeared only in the Mesozoic, meaning the only way they could have possibly cloned a Meganeura is if it was living alongside dinosaurs.

1. Entry Time: Undetermined
2. Trope Maker: Educational media.

The Super-Millipede of the Coal Forests: Arthropleura **

While plenty of regular-sized arthropods existed in the Carboniferous, those guys don't gain much attention in media because: A) they were basically identical to today's insects; and B) Bigger Is Better. And among the giant arthropods, the biggest of them all was Arthropleura.

Arthropleura ("articulated side") was a 2.5m/8ft long millipede, the biggest known land arthropod of all time (one group of aquatic arthropods, the eurypterids, produced even bigger forms — we'll get to them in a bit) It was also well-armored, to the point that it could be considered a living tank. But like modern millipedes, it was an inoffensive herbivore that fed on the rotting vegetation abundant in the swamp-forests of Late Carboniferous Europe and North America. Arthropleura wouldn't have resembled a millipede at first glance: wide and flattened, it more resembled an overgrown trilobite, although there are modern millipedes with a rather similar body shape, albeit obviously much smaller. Its fossil tracks are a common find in Carboniferous rock, looking like miniature railways. We don't know if it was able to rear up like a cobra as portrayed in Walking with Monsters and Prehistoric Park, given its weight.

So why did land arthropods reach such a large size in the Carboniferous? The common explanation goes like this: the oxygen content at the time was much greater than in every other period, and the respiratory system of insects and land arthropods prevents them from growing very large (over a certain size, they just can't breathe) — as a result, the upper limit an insect can grow to depends on the quantity of oxygen in the atmosphere, and more oxygen —> bigger size. However, this has been called into question, as Meganuera, Arthropleura, and the rest all first appeared before the oxygen levels rose to ridiculous levels and survived into the Permian when oxygen levels nosedived. The new theory is that they were simply able to get massive due to a lack of competition with large terrestrial vertebrates: once the first large land animals evolved, the giant ground-based arthropods went extinct, while large flying insects continued into the Triassic, vanishing shortly after the appearance of the first flying vertebrates — the pterosaurs.

Despite this critter's size and appearance, Arthropleura historically got little presence in the media, outside of books on prehistoric life. However, after it appeared on Walking with Monsters, it quickly became a common sight in documentaries about life before the dinosaurs and other prehistory-themed pop culture. The most noteworthy appearance of an Arthropleura in a non-educational work was Primeval, which instead decided to portray it as a giant venomous centipede.

1. Entry Time: 2005
2. Trope Maker: Walking with Monsters

Ancient Sea Critters: Pterygotus & Cameroceras *

Today, marine invertebrates are by far the most diverse animals on Earth: almost every zoological phylum is represented in the oceans, just like in the past. Among Paleozoic sea invertebrates (apart from trilobites and the earliest ammonites), the eurypterids and nautiloids are the most iconic in docu-media.

Eurypterids are popularly known as "sea scorpions", but are not true scorpions, or even arachnids — rather, they are cousins of both arachnids and horseshoe crabs (which, while we're at it, aren't crabs or any other kind of crustacean). They did look a bit like scorpions though — if scorpions evolved lived to underwater, that is. They had large compound eyes with excellent vision, lobster-like bodies, and six pairs of limbs; they also had two respiratory systems — one for breathing underwater and another able to breathe air. The second set, combined with fossil trackways, tells us they were likely able to come onto land for brief periods, possibly to breed. Like trilobites, the babies resembled miniature adults and grew by moulting their exoskeletons. Two main groups exist: the free-swimming eurypterines (whose last pair of limbs became swimming paddles) and the bottom-dwelling stylonurines (which had spidery legs) — the former were active predators, the latter bottom-feeders. First appearing in the Middle Ordovician, they ruled the oceans as top predators until the evolution of jawed fish, which almost completely outcompeted the eurypterines in the Devonian and forced the stylonurines to move inland and evolve into freshwater animals. The last eurypterines died out in the Early Permian, while the stylonurines were killed off in the colossal Permian mass extinction.

The most famous eurypterids are the Middle Silurian-Late Devonian pterygotid eurypterines, which could reach over 2m in length — the biggest arthropods of all time (the smallest eurypterids were as big as paperclips!). The namesake and most famous of the pterygotids (or "seraphims") was the 1.7m-long Pterygotus ("the finned one" or "the winged one"). Like all pterygotids, Pterygotus had lobster-like claws on its first pair of limbs and a paddle-shaped tail — adaptations for life as a powerful, fast-moving predator of the water column able to compete with early jawed fish. Being among the biggest and fiercest of its kind, Pterygotus is a popular inclusion in docu-media about the Paleozoic: it memorably appeared in Walking with Monsters as the top predator of the Silurian, ambushing the giant, aquatic true scorpion Brontoscorpio to feed its babies.

Unlike the trilobites, eurypterids, and ammonites, nautiloids are still alive in today's world in the form of the chambered nautilus found in the deeper waters of the Indo-Pacific. As cephalopods, nautiloids were likely the ancestors of the ammonites and coeloids (octopus and squid): they likewise have tentacles, a beak, and a siphon for jet propulsion. However, compared to ammonites and coeloids, they have much simpler eyes with poor vision, up to a hundred small tentacles without suckers (rather than just eight or ten), and no ink sac. And while their chambered shells are easily mistaken for those of ammonites (and serve the same purpose of defense and buoyancy), nautiloids have simple smooth walls to their chambers while ammonites have wrinkled, curved walls: also, an ammonite's siphon forms under the animal's tentacles, while a nautiloid's is in the middle of them. And whereas coeloids and ammonites produced numerous planktonic young, nautiloids produce few young, and they resemble tiny versions of the adults. Nautiloids first appeared in the Late Cambrian, but were most numerous during the Ordovician and Silurian: they entered a steady decline in the Devonian due to competition with ammonites and coeloids — in the Oligocene and Miocene, their numbers crashed until only the modern species remained. For a long time, their Cenozoic near-extinction was attributed to the oceans getting colder, but in 2022, new research revealed the evolution of seals also played a role: seals eat shelled prey by biting on and sucking/shaking the soft-bodied animal out, and the decline of nautiloids worldwide coincides with the arrival of seals in the area — there are no seals found in the places the modern nautilus inhabits.

Although the modern nautilus possesses a helix-shaped shell, many Paleozoic nautiloids possessed long, straight shells resembling ice cream cones. These nautiloids are dubbed "orthocones", and the most oft-depicted form is the Ordovician-Silurian genus Cameroceras ("chambered horn"). Popularly nicknamed the "giant orthocone", many paleo-books and documentaries will tell you that Cameroceras was the largest of all nautiloids, up to 9m/30ft in length. This interpretation most famously appeared in Sea Monsters, feeding on sea scorpions and giant trilobites. However, this is no longer considered a valid interpretation — as it turns out, those alleged 9m/30ft Cameroceras specimens actually belonged to a different genus, the already-known Endoceras, and were in fact only 6m/20ft. Today, Cameroceras is now believed to have been about 1m/3ft long: although some experts think that Endoceras and Cameroceras are the same, potentially allowing the latter to regain its title. Regardless of identity, the giant orthocone was doubtlessly a formidable predator and certainly the biggest animal to have ever lived up to that point in Earth's history. The last orthocones vanished during the Triassic, leaving only their spiral-shelled brethren today, the very last of an over 400-million-year-old lineage.

1. Entry Time: undetermined for Pterygotus; 2003 for Cameroceras
2. Trope Maker: educational books (Pterygotus); Sea Monsters (Cameroceras)

Unshelled or Shelled?: the Belemnites *

The fossils of many marine invertebrates are so common and widespread that before they were understood to be the petrified remains of long-gone animals, people made up all sorts of stories about them. Ammonites, for instance, were believed to be stony horns ("ammonite" comes from Amun, an Ancient Egyptian deity who was often portrayed with rams' horns), or petrified snakes — some folks even sculpted snake heads on the shells' extremities to make them look like more serpentine! The lesser-known belemnites (technically belemnitids), with their straight pointed shape, were believed to be stony arrows, or even the Devil's fingers!

Belemnites were a group of cephalopods exclusive to the Mesozoic era: like their ammonite contemporaries, only their shells are usually preserved. This shell was straight, arrow-shaped, and inside the animal's body, invisible in life; belemnites would resemble simple squid or cuttlefish if alive today, and indeed, they are part of the same group that contains modern octopus, squid, and cuttlefish — the coeloids. Note that squids and cuttlefish have internal shells too (octopuses have lost them entirely), but this is a much simpler structure than in belemnites: almost entirely gone in the squids' case. Additionally, the belemnite's body extends beyond the fins, whereas a squid's fins form at the very end of the body. Most belemnites were highly active animals adapted for moving at high speed in the open ocean, and they were able to do the same things modern squid do: spraying ink, swimming using the lateral "fins", catching prey with their suckers, seeing complex images with their eyes. Unlike squids however, belemnites went extinct at the end of the Cretaceous alongside the ammonites when the asteroid struck. In popular media, belemnites tend to be shown as ambient animals for prehistoric placements, but it's not uncommon to hear them referred to as proper squids, which they weren't. And despite appearances, they were not the ancestors of squids either, bur rather the most primitive branch of the coeloid family tree.

1. Entry Time: undetermined
2. Trope Maker: educational media

The First Predator of the Seas: Anomalocaris *

About 540 million years ago, the "Cambrian Explosion" occurred, marking the sudden appearance of a staggering variety of complex lifeforms — some of the first-ever animals. And among the "wonderful life" that emerged in this era, the most famous of all is Anomalocaris ("odd shrimp"). This, of course, is because it was one of the largest animals of the Cambrian and among the earliest examples of a large apex predator

Living in the shallow seas that cover what is now Canada (alleged Chinese specimens have since been reclassified as relatives), Anomalocaris means "anomalous shrimp": this name reveals a singular Real Life case of Mix-and-Match Critter. Initially, the name was invented in 1892 for one of its "arms", which was mistaken for the tail of a shrimp. Then, its circular mouth and body were found separately, each of them believed in turn to have been distinct organisms: the mouth was first described as a jellyfish named Peytoia, while the body was thought to be a sea cucumber named Laggania. In 1966 however, scientists found new fossils showing that the "three" animals were actually fragments of one bigger animal, with Anomalocaris taking priority. However, the original Peytoia and Laggania fossils have since turned out to belong to a related animal that has kept the Peytoia name (Anomalocaris' mouth, while similar in shape, was structured slightly differently).

Like many "Cambrian Explosion" lifeforms, Anomalocaris was an extremely early member of a modern phylum — in this case, the arthropods. Specifically, Anomalocaris was a member of the Dinocardids. And like a lt of its fellow "Cambrian Explosion" animals, it looked like something from another planet — it had a soft body with numerous lateral "fin-like structures in place of articulated legs to swim above the seafloor, compound eyes on stalks, a pair of mustache-like "arms" at the front of its head (the alleged "shrimps" that gave it its name), and a circular mouth on the underside of its head with "teeth" placed in a circular fashion like a lamprey (this was the alleged jellyfish).

Anomalocaris gets a lot of hype in docu-media as "the first Sea Monster", but at only 56cm/2ft long, it would have been very harmless by today's standards. Nonetheless, Anomalocaris and many of its relatives were the biggest and fiercest animals of their day — twelve to six times larger than their prey. Bizarre, finger-sized animals like Hallucigenia, Pikaia, Wiwaxia, and Opabinia (the last one also a dinocardid) were hunted by Anomalocaris, which would have snatched them with its "arms" and sucked them into its maw. In fact, it's quite possible that the evolution of predatory dinocardids set up the important role of predators in ecology and evolution, driving animals to evolve a variety of defenses or to directly compete with their predators and each other.

While the strange animals of the "Cambrian Explosion" are a staple of palaeo-books, Anomalocaris is the only one that has made to make regular appearances in popular media, such as Walking with Monsters, where its size is exaggerated to that of a human! Interestingly, "Cambrian Explosion" lifeforms are extremely popular in Japan (Hallucigenia, for instance, plays a major role in Attack on Titan as part of the eponymous giants' origin story), and Anomalocaris is again the most popular. For example, the Pokémon Anorith and its evolved form Armaldo are based on it, while franchise rival Digimon features Anomalocarimon. Evidently, Japan's love for the bizarre extends even to extinct animals!

1. Entry Time: Early 2000s
2. Trope Maker: Walking with Monsters and Pokémon

Other prehistoric invertebrates

Sorry, these aren't here. If you're looking for prehistoric crustaceans, rudists, brachiopods, bryozoans, cystoids, blastoids, graptolites, chalcicordates, nummulites, and others, see here.

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