A list of common misconceptions about paleontology in fiction. For help with the names of the various extinct creatures, see Prehistoric Life.

Common Inaccuracies In Media

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Paleontology

Paleontology in General

The Prehistoric Monster trope goes hand-in-hand with this one, especially in older works. Occasionally this is due to Science Marches On, but usually it is done deliberately, either due to audience appeal, simple laziness (especially when a Slurpasaur is involved), or as a homage or call-back to earlier works.
Any work claiming that prehistoric reptiles like dinosaurs, pterosaurs and marine reptiles were all "giant lizards". Out of all Mesozoic megafauna, only the mosasaurs fit that description; dinosaurs and pterosaurs were as far from being lizards as it was possible to be while still remaining saurian reptiles; in fact lizards (including snakes) are further away on the evolutionary line from dinosaurs than birds (and crocodylians) are. The relationships of marine reptiles like ichthyosaurs and plesiosaurs to other reptiles are less certain but they were certainly not lizards.^note
Prehistoric animals are often shown as being much larger than they really were. It's also common for works to forget that not all dinosaurs and other prehistoric animals were big, with only the largest prehistoric creatures shown. In fairness, preservation bias means that few fossils of small animals have been found, so the dinosaurs people know of were frequently large in the first place. This trope can be exaggerated however; the average dinosaur was in fact the size of a bison (roughly as tall as a man), rather than merely as big as a sheep as has sometimes been assumed.
Anachronism stewing is endemic with popular depictions of prehistoric times, whether it is humans using Triceratops to plough fields, or depicting T. rex and Stegosaurus living alongside each other, despite the fact that they never would have met in real life. In fact the time between Tyrannosaurus and Stegosaurus is significantly greater than that of Tyrannosaurus and human beings.^note This type of thinking probably comes from the idea that "prehistory" is just one single, vague time period, not considering that the scale of geologic time is unfathomably vast.
Treating any Cenozoic megafauna as an Ice Age animal, despite the last "Ice Age" occurring only 2.6 million years ago during the Pleistocene. This misconception is probably because the most famous prehistoric mammals lived during the Ice Age, particularly the woolly mammoth.^note
Confusing paleontology and archaeology. Paleontology studies remains of past life forms (and their activity). Archaeology studies past human cultures. It doesn't help that paleo and archaeo both mean "ancient".
It's a commonly-held belief that the discoveries of Megalosaurus and Iguanodon were the first documented fossil finds; they weren't. Mosasaurus, Megatherium, Pterodactylus, ichthyosaurs and plesiosaurs were all found before them as far back as 60 years. This fact doesn't make them any less significant, considering they were the first dinosaur finds and arguably where paleontology really took off^note; they were just not the first fossil discoveries.
People often mess up classification of extinct animals; for example, calling all dinosaurs birds. To put this in perspective, this is like saying all mammals are apes. Birds are a subgroup of dinosaurs, not the other way around.
Cryptozoology, particularly the trope of Living Dinosaurs, is prone to outlandish claims that don't reflect accurate palaeontology:
- Any time someone claims that any types of large animals actually survived and is out there. While it is true we have found some creatures that we thought went extinct but actually survived (most famously coelacanths), it is very unlikely we wouldn't know about the really large ones like plesiosaurs, megalodon, Gigantopithecus, and the other prehistoric animals that are most often the subjects of these claims.
- Thanks to Science Marches On a lot of accounts of these animals don't add up in hindsight. For example, plenty of eyewitnesses claim to have seen the Loch Ness Monster get up out of the water and walk on land. The problem with identifying such an animal as a plesiosaur is that we now know plesiosaurs simply couldn't do that. Another is the theory that Bigfoot is a Gigantopithecus, even though Gigantopithecus most likely did not walk upright like Bigfoot is said to.
- Additionally, such animals used as potential explanations for cryptids hinge on the notion that the animal in question has never changed due to evolution for thousands or millions of years. While it isn't impossible for an animal to remain relatively unchanged over tens, or even hundreds of millions of years, it's relatively rare. This would be especially true when said cryptid is reported in an environment that is radically different than the environment it is said to have evolved in. For instance, while the giant ground sloth Megatherium lived in grasslands and open plains, the Mapinguari of Brazilian Folklore, which some cryptozoologists theorize is a surviving Megatherium, is said to exist in swamps and rainforests. Such a creature would have to radically alter its feeding habits and behavior to the point where it would probably look only tangentially similar to a Megatherium. And that's still a less radical change than the notion that a megalodon could go from open ocean hunter to a deep-sea fish and remain unchanged.

Evolution

A lot of people think evolution equals improvement; that's not entirely true. While evolution can improve an animal's survivability and success (just look at us humans) it can also lead to Crippling Overspecialization. One example is saber-tooth cats. They evolved their sharp teeth and strength to overpower and cut through animals hides. Unfortunately this made them too slow to capture more agile prey once their main food source died out.
In a similar vein, evolution is not a single, forward-moving line. If it were, there would be no fish, reptiles or amphibians on Earth today. It's bushy and chaotic, with multiple offshoots of the same species as they evolve according to their own environments. That's why humans could coexist for tens of thousands of years with both Neanderthals and Homo erectus; why wombats were preyed upon by Thylacoleo, which was essentially a giant predatory wombat; and, despite what creationists may say, why there are still apes; why birds coexisted with bird-like dinosaurs; and Tiktaalik, the earliest known example of a fish-amphibian transition, could coexist with vertebrates already on land.
Evolution is not random. Mutation is, which is what gives rise to new traits, but natural selection, the filter by which mutations are selected for their utility, is brutally directed. Animals and plants with disadvantageous traits are all-but-immediately removed from the gene pool, while those with advantageous traits can completely overrun an ecosystem. This, of course, can also lead to the organisms' extinction as they deplete their food supply. There is a misconception that animals and plants "live in harmony" with each other, when they are simply what remains when every disadvantageous trait has been weeded out. What we call an ecosystem is really the survivors of a neverending war, constantly running to stand still.
Any time prehistoric animals are shown to be evolutionary dead ends that deserved to die out. A lot of this comes from earlier works in paleontology up until the Dinosaur Renaissance. Now that we know a lot more about evolution and the history of Earth this is seen as a shallow assumption especially comparing it to dinosaurs. If anything, dinosaurs are probably one of the most successful animal groups to ever live, dominating the earth for about 165 million years, only being replaced by mammals due to a random and sudden global catastrophe, and still existing today as birds.
The idea that of evolution is simply strong survive and the weak die out. While stronger animals usually benefit in the short term, in the long term a lot of those weaker animals last a lot longer. This is because being smaller they need less food to survive, and tend to be more adaptable and not suffer from Crippling Overspecialization. In fact when things start to get tough a lot of animals will get smaller over generations. When mass extinctions occur, it is invariably the "weakest" animals that survive. No animal above 25 kg in size survived the K-Pg extinction, for instance. Evolution isn't about "survival of the fittest" (Darwin didn't even coin that phrase), but about survival of the survivors. What do the T. rex, the sabre-toothed cat, the terror bird and the megalodon all have in common? They're all extinct. And we didn't do it. Conversely, many ludicrously "unfit" organisms from the bigger/stronger/faster = better perspective, such as dodos, sloths, koalas, seahorses and giant pandas, managed to hang on for millions of years by being just fit enough to survive in their habitats. Believe it or not, the panda is the oldest species of bear in the world.
Evolution isn't just about competition. Natural selection takes any strategy that works, and that includes cooperation. Everything from the mitochondria in our cells (which were originally bacteria-like organisms that infected our ancient, single-celled ancestor) to ants farming aphids to clownfish living in anemones is literally living proof of this. There's even a word for it: symbiosis, specifically mutualism (both benefit) and commensalism (one benefits, the other doesn't mind) which are the positive sides of symbiosis. Predation and parasitism would be the common antagonistic flavours.
A very common element of Lost World settings featuring prehistoric life seems to presume that just because the fauna has been "forgotten by time" that it means they will literally not change at all for millions of years (a very common example is living dinosaurs in immediately recognizable genera like Stegosaurus or Tyrannosaurus). Obviously in reality, just because a life-form inhabits an environment that is isolated from the rest of the world doesn't mean it'll stop evolving. It's extremely rare for a species to remain completely unchanged for tens of millions of years (even many so-called "living fossils" are actually recently evolved species that happen to belong to very old lineages), particularly for large terrestrial animals like dinosaurs, which may evolve into another species within a few hundred-thousand years in some cases.

Paleoart

Paleontologist Thomas Holtz Jr. has used the term "dinosaur in a parking lot◊" to describe paleoart that places the animal in complete isolation, removing it from its ecological context.
"Paleoart meme" is a term used to describe when artists assume a previous artistic depiction is 100% on-point and copy it despite the fact that a large portion of it was speculation (for example, think of how many depictions of Deinonychus hunting Tenontosaurus you may have seen). That one picture or interpretation becomes the status quo despite the fact there is no proof of that characteristic. This has not only plagued the public perception but even the paleontology community itself. There have been steps to avoid this in paleoart.
The act of "shrinkwrapping." More prevalent in late 1980s-mid 2000s paleoart, shrinkwrapping is basically when artists draw animals as, essentially, skeletons with skin clinging to the bones and little or no fat or muscle in between, so the shapes of the bones is visible. For comparison, almost no animal in the modern day, including birds and crocodilians (the animals most closely related to dinosaurs), looks like a walking skeletal anatomy diagram unless it's starving or dead, so we can be pretty sure that dinosaurs and their neighbors definitely had much more meat on their bones than that. Lately, people have been avoiding this more often. To sum up just how WRONG shrinkwrapping would look, this ugly thing◊ is what a domestic cat would look like if it was reconstructed with only minor additions of skin and flesh on the skeleton, completely ignoring fur and soft tissues. Most prevalent on dinosaurs and pterosaurs, shrinkwrapping has of course been less seen in depictions of extinct mammals and animals with close living relatives. Since The New '10s, the problem with this style has become better-known and more artists are taking efforts to avoid it.

Fossils

Complete fossils are not found most of the time; occasionally we find really well-preserved skeletons, which is more common for smaller animals, but for bigger animals most of the time it's just bits and pieces. For example, there are only fifty known T. rex skeletons in the entire world, and even then, the most complete one is only 85% intact. This is the reason older prehistoric animal reconstructions look drastically different from today. They only had so much to work on back then compared to what we have now.
The fossils on display at museums are not always the original specimens; sometimes they are, but even then models are often used to fill in the blanks (see above). Most of the time they're reconstructions of the bones rather than the bones themselves. This has to do with how fragile and (in large animals) heavy a lot of fossils are. Remember, a fossil bone is rock, nowhere near as light or resilient as the original bone. The actual fossils are kept in museum collections that are off-limits to the general public.
Any time a fossil find is called a "prehistoric crime scene". Yes, paleontology and forensics have a few superficial similarities, but, leaving aside the fact that predators, by definition, do not commit murder, paleoecology is not just about "who killed whom". A fossilized animal may have died from any number of causes, from disease, drowning or even old age, rather than predation, and the layout of a fossil site can reveal far more about a local environment than just the animals in it, from the plant life to the temperature to whether it was by a lake, river or sea.
Anytime fossilized bones (and, by extension, their replicas in museums) are colored pure white like a regular bone.
The idea that oil and other fossil fuels are made from decomposed dinosaur remains, while a popular statement, is completely false. Petroleum oil is made primarily of decomposed aquatic microorganisms such as zooplankton and algae, and not dinosaurs. On that note, coal also does not come from dinosaur remains as popularly assumed but rather decomposed swamp vegetation that formed into peat (although unlike oil, coal does sometimes contain animal remains).

Dinosaurs

Dinosaurs in General

Anything being called a dinosaur that isn't: Pterosaurs such as Pterodactylus; giant sea reptiles such as plesiosaurs, ichthyosaurs and mosasaurs; pre-dinosaur reptiles like Scutosaurus; synapsids such as Dimetrodon (which were not, strictly speaking, even reptiles, but proto-mammals); any modern "scaly" reptiles (even closely related extinct giant species like Deinosuchus or Megalania); fish or, Darwin forbid, mammals. In short, dinosaurs are usually generally defined as the last common ancestor of Saurischia and Ornithischia and all of its extinct and living descendants; this can be applied to the most recent ancestor of both Iguanodon and Megalosaurus ^note, or Triceratops, one of the last non-avian dinosaurs to live, and modern birds.
Anything being called not a dinosaur that is, such as Archaeopteryx or modern birds. Birds being regarded as different from dinosaurs is acceptable for 1980s/1990s works, but not today, as the modern consensus is that all birds are descendants of small feathered dinosaurs from the end of the Jurassic. Or more accurately, birds and other theropod dinosaurs share a recent common ancestor from which they diverged at the end of the Jurassic.
Describing dinosaurs in general as big. While some are famous for being the largest animals on land, most dinosaurs were in fact small (and still are today). Thankfully, this has become a dying trope with the influence of Jurassic Park.
Dinosaurs were never scientifically considered to be "terrible lizards". When Sir Richard Owen first coined the word "dinosaur", he referred to Dinosauria as a "distinct tribe or suborder of Saurian Reptiles", thus intended the term to mean "Fearfully-Great Reptile" in Greek. However, the Greek deinos can mean "terrible, potent, awe-inspiring, or fearfully-great" and sauros can mean either "lizard" or "reptile", thus "Terrible Lizard" is also a technically correct word-for-word translation that just conveys entirely the wrong idea.
Cold-blooded dinosaurs. In particular, dinosaurs are often depicted as being slow, sluggish and unable to survive, let alone function, in cold temperatures. This old idea was basically stemmed from "They were reptiles similar to crocodiles, and crocodiles are cold-blooded". In reality, the anatomy of dinosaurs suggests they were warm-blooded and led active lifestyles, some of them being nocturnal, and there's evidence that some genera thrived perfectly fine in snowy environments (which are often said not to have existed in the Mesozoic era). While it's now considered doubtful that large dinosaurs were endothermic, they still would have been warm-blooded due to a larger body producing more heat and losing less (i.e. mesothermy). The concept of active, warm-blooded dinosaurs is actually Older Than They Think, going all the way back to the Victorian era (notice how the Crystal Palace dinosaurs are more similar to mammals than lizards or crocodiles), with the sluggish, cold-blooded dinosaurs coming into popularity during the rejection of the dinosaur-bird connection from the 1920s to 70s.
Dinosaurs dragging their tails along the ground. Another old idea based on "Well, crocodiles do it, so they must have". In fact, dinosaurs walked with their tails held rigid due to their weight; most groups have thick caudal vertebrae likely supported by a lot of muscle just to hold them up and power the legs. This early misconception led to the academically approved vandalism of several dinosaur skeletons, to the point of even breaking the bones of some to make the tails drag as desired. While a few tail traces of dinosaurs have been discovered, they seem to be that of individuals crouching or dipping their tails down as opposed to walking. There is speculation Spinosaurus was an exception to this due to its much shorter legs and possibly upright neck, but then, Spinosaurus was effectively a gigantic, convergently-evolved dinosaurian crocodile, and so is the only true dinosaur that actually fits the original conception of dinosaurs as giant crocodiles.
- Dinosaur tails are often shown to be extremely bendy as if they are made of rubber. In real life, dinosaurs had relatively stiff tails, mostly used as counterbalances as the animals were active. Some even had bony tendons to stiffen the tail. However, some studies have suggested stegosaurids have a higher tail dexterity than previously thought.
Dinosaurs having the wrong postures. Most notable examples are small-armed bipeds like Tyrannosaurus walking in a tripodal stance with an upwards-slanting spine and quadrupeds like Triceratops having sprawled limbs like lizards. Dinosaurs couldn't walk with a sprawled posture; their weight mandated that they walk with their legs straight under them, because no muscle could support it sprawled. Dinosaurs with reduced forelimbs held their spines parallel to the ground, since all their weight is placed on their hips. If they walked in a tripodal stance, they would suffer strain or even dislocation in their joints. The tripodal posture thinking likely stemmed from observations of the only large bipedal standing animals with long tails that still exist, macropods (kangaroos, wallabies, etc.), which also led to the idea some "hypsilopodonts" were tree-dwelling animals. It should be noted that the only large bipeds with reduced forelimbs alive today, ratites (ostriches, emus, cassowaries, etc.), hold their spines horizontally.
Dinosaurs only colored grey, green or brown. Another ancient trope derived from the "they were just huge crocodiles" line of reasoning. Crocodilians are grey, green or brown because they are adapted as semi-aquatic ambush predators that depend on camouflage, but in fact, most reptiles today have a wide range of skin colorations and rely heavily on visual communication (having a wider spectrum of color vision than mammals). It is likely that at least some dinosaurs had vibrant colors and patterns. That is not to say no Mesozoic dinosaurs were comparatively drably colored, but brightly-colored representatives probably weren't rare.
- It was once thought the coloration of dinosaurs would be something that could never be truly known. A few years ago a method to figure it out was discovered at long last. What had been assumed to be just dirt or bacteria in fossils turned out to be preserved melanosomes, which could be compared to the melanosomes of living animals to figure out the color they would have been when the animal was alive. There now are complete and highly accurate restorations of the colors and patterns of several dinosaur species, an extinct penguin, and two other birds, with more currently being researched. Several of them have turned out to have vibrant colors.
Dinosaur eggs will often be shown as gigantic, often over six feet tall. In reality larger eggs require thicker shells, but the shell has to stay air-permeable. This limits the size of porous calcium carbonate eggshell for dinosaurs and recently-extinct large birds to about 15 liters in volume and 35 centimeters in diameter — not much bigger than a basketball. No larger eggs have ever been ever found. Eggs made from less rigid materials were even smaller. Not to mention that a six-foot egg would also be implausible due to the Square-Cube Law. Funnily enough, the largest dinosaur egg known was laid by a bird that went extinct less than a millennium ago: Madagascar's elephant bird (Aepyornis maximus).
Dinosaurs and pterosaurs with an unnatural number of fingers, toes and/or claws. Archosaurs (the broader group in which dinosaurs, pterosaurs, crocodilians and their relatives belong) by default have four toes on the back feet, and five on the front feet, but only three of which have claws (as seen here◊); therefore dinosaurs could only have this number or fewer (the other extreme is some advanced titanosaurs, which had no fingers, toes, or claws, their limbs ending in fleshy stumps). The most common errors include giving Tyrannosaurus too many fingers, giving herbivores too many claws (often resulting in inaccurate elephant-like feet), and giving pterosaurs too many elongated fingers (resulting in bat-like wings) and too few wing claws (or too many wing claws in the case of nyctosaurids, which are known for lacking those).
Dinosaurs constantly making noise such as roaring and shrieking. Needless to say real animals don't vocalize nearly as much. Evidence currently suggests that dinosaur vocalizations were potentially more like those of crocodilians than the complex vocalizations of many modern birds (which make them with a specialized organ known as a syrinx, which so far appears to be unique to birds). Depictions of T. rex having a Mighty Roar is more Rule of Cool than based on any evidence. Still, that doesn't mean the sounds it actually made wouldn't have freaked you out.
It's increasingly looking likely that dinosaurs had lips that covered their teeth so when their mouths were closed the teeth would not be visible, like in lizards or mammals, as opposed to the exposed teeth of crocodiles (or this◊ compared to this◊). By extension this is also probably true for ancient crocodile relatives that lived on land, with the modern lipless condition being a derived trait.
On a related note, depictions of dinosaurs with flexible mammal-like lips are very unlikely. If dinosaurs had lips, they would almost certainly be stiff and immobile like those of lizards (as mobile, fleshy lips are only known in mammals among all vertebrates, probably as an adaptation to nursing on teats) which means they would not be able to snarl, bare their teeth, or emote with their mouths outside of simplistic opening and closing.
It would be logical that dinosaurs might have shed their old skin as all reptiles (including birds, which are technically reptiles) do it, but expect this to be portrayed as molting large patches of skin in the same manner as snakes or lizards. However, technically speaking, the "scales" of dinosaurs (and, by extension, archosaurs in general) are not actual scales like on lizards and snakes but rather scutes; they form and behave in different ways from lizard scales. In real life, dinosaurs would have shed individual scutes like crocodiles, especially given that birds molt this way (feathers are modified scales after all, plus the scales on birds' feet and legs are shed as well). This is confirmed by a 2018 discovery of shed dinosaur scales.
Dinosaurs are sometimes portrayed performing autotomy with their tails and regenerating them like lizards; needless to say, they did not do this.
Dinosaurs having pronated hands i.e. the palms of the hands facing backwards toward the body, an artistic convention now derisively called "zombie" or "bunny" hands. In real life, dinosaur hands faced each other like a person about to clap. If they tried to pronate their hands, they would break their wrists.
Large dinosaurs with wrinkly, elephant-like skin, probably coming from the thinking that "elephants are big, dinosaurs are big, therefore dinosaurs were elephant-like". Of course we have overwhelming evidence that indicates that when they weren't covered in feathers, dinosaurs were mostly covered in small pebbly scales. Bonus points if the animal is also depicted as being uniform grey.
Dinosaurs being the ancestors of lizards. Not only are these reptiles from two separate branches on the biological family tree (lizards are lepidosaurs, while dinosaurs are archosaurs like crocodiles) but the sprawled posture of lizards is a primitive trait, and re-evolving lost traits is near to impossible.
- It should be noted that all known advanced forms of lizards have either become entirely aquatic, in the case of mosasaurs, or lost their limbs, in the case of legless lizards and snakes.
Dinosaurs with plantigrade or human-like feet, which is possibly a result of mistaking the ankles for knees. Dinosaurs are mostly digitigrade (walking on their toes) or semi-digitigrade (toe-walking but with the heels closer to ground), with the exception of Therizinosaurs and some diving birds like loons.

The Age of the Dinosaurs

The popularity of the film Jurassic Park (1993) led to a pan-medial explosion in use of the term "Jurassic" to describe the dinosaurs' time period. Actually, the Jurassic Period only comprised the middle third of the dinosaurs' era (in between the earlier Triassic and later Cretaceous), which in its entirety is called the Mesozoic. This was lampshaded frequently in Michael Crichton's original novel; probably because he didn't want to seem scientifically illiterate but wasn't about to give up such a cool name.
The Age of the Dinosaurs is often depicted as a dark, impenetrable jungle from end to end. In fact, the Mesozoic was a vast span of time encompassing a huge range of temperatures which, while all warmer than today, led to a plethora of different climates. The Early Triassic, thanks to Pangaea, was one huge desert, while the Late Cretaceous, the time of T. rex, was surprisingly cold and may have seen snow in some areas. Many time periods in the Mesozoic, such as the Mid-Jurassic and Mid-Cretaceous, do fit the tropical stereotype, though many of the plants we associate with the tropics are flowering broadleafs and so didn't come to dominate the landscape until the age of the dinosaurs was nearly at an end.
Whenever the topic of a real Jurassic Park's feasibility comes up, there is a guarantee that someone will shut it down with the claim that dinosaurs got so big because there was more oxygen in the athmosphere when they were alive, so they would collapse and suffocate in today's world. This isn't true - oxygen levels for most of the Mesozoic were actually similar to today, and the only time in Earth's history they were higher was in the Carboniferous period (360-300 million years ago), 70 million years before the first dinosaurs evolved. Dinosaurs could reach gigantic sizes because they had air sacs in their bones, like birds, and these sacs may have first evolved in the Pangaean desert when trees and in consequence oxygen were scarcer than today. The "grew larger because of the higher oxygen concentration" explanation applies to the large arthropods of the Carboniferous, which could only exist in that time because most arthropods have no lungs, but a tubular system that takes oxygen directly from the air to their cells, and this system is very inefficient in large animals unless you happen to have a great concentration of oxygen in the atmosphere.
Like the Cretaceous and Jurassic; the Triassic is seen as the era were dinosaurs ruled. Dinosaurs weren't doing badly but the era had extreme diversity in terms of life, calling it the age of dinosaurs would be ignoring all that life. In fact, the beginning of the Triassic didn't even have dinosaurs. The age started at 252 million years ago and dinosaurs appeared 240 million years ago. It was only after the End-Triassic extinction did dinosaurs become the dominant creatures on the earth during the Jurassic.
It’s often said that we have no idea what killed all non-avian dinosaurs; the truth is we are pretty sure that the meteorite was the final nail in the coffin for them, though it was the climax to a lot of other events beforehand (See below).
A lot of people think it was just the meteorite that killed the dinosaurs, but later claims amended this by suggesting that it was just the end for a really bad day for them, with the Cretaceous seeing a dropoff in the number of dinosaurs, usually blamed on the changing climate and other factors. This newer theory has in turn started to take a lot of hits in recent years, though, as discoveries from all over the world are suggesting that non-avian dinosaurs were still going strong even to the very end of the Cretaceous, and it really was just the meteor that did them in. Discoveries of new dinosaurs like Dakotaraptor, Chenanisaurus, and Yamanasaurus indicate that even at the end of their age, dinosaurs were continuing to diversify. It’s often speculated that if the meteor had hit at any other time, the dinosaurs would have been able to bounce back even more easily than they actually did - and as it is, they never went completely extinct as was once thought, as birds are still with us today. On the other hand, marine ecosystems were under stress shortly before the end of the Cretaceous due to other factors.
The belief that an ice age killed the dinosaurs. Not only were they dead for 60 million years before the start of the ice age, but the time immediately following the dinosaurs' extinction was actually substantially warmer. There's also plenty of evidence for polar dinosaurs, so it's likely some could have survived an Ice Age.
Forgetting that Pangaea drifted apart about 200 million years ago, at the beginning of the Jurassic. By the Late Cretaceous, the continents would have been arranged closer to where they are today.

Saurischians

Theropods in General

Whenever a theropod's skull is drawn without the antorbital fenestra, which is a common occurrence in animation and illustration. Also, the antorbital fenestra is often mistaken for the eye socket, which results in certain theropods like Tyrannosaurus being portrayed with a shorter snout than in real life.
Not all theropods held their spines parallel to the ground. The reason for horizontal stances in theropods is due to the center of gravity being placed in their hips coupled with short forelimbs and long tails. Theropods with more upright stances such as therizinosaurs and penguins tend to be top-heavy with longer forelimbs and short tails.
The popular depiction of theropods with their teeth sticking out of their jaws is also inaccurate. The very fact that their teeth had enamel indicates theropods had reptile-esque lips covering the teeth; enamel needs to be kept moist to protect the teeth from rotting. The very function of lips is to protect enamel-coated teeth from rotting, so since dinosaurs had enamel-covered teeth, they more than likely had lips. A discovery in 2017 of a Daspletosaurus skull with detailed preservation of the jaw bones, which studies found to be more analogous to crocodilian jaws than lizard jaws, led to some calling for a lipless condition, but other paleontologists disagree with this, claiming that said preservation does not indicate lack of lips. It should also be noted that exposed teeth in crocodiles is a very specific adaptation towards piscivory (fish-eating), and even then, other fish-eaters like monitor lizards and otters retain lips.
Some people think all theropods were carnivores. Many were, but some (like Therizinosaurs) actually ate plants, or at least had an omnivorous diet (like ornithomimosaurs). And of course today’s theropods, birds, include many herbivores, like ostriches, swans and turkeys.
Improbable feathering in coelurosaurs. Some of the most common errors are giving too sparse a coat, wrong types of feathers, and giving them the wrong wing shape. In maniraptoriformes (the group that includes dromaeosaurs, ornithomimosaurs, and birds, among others), the primary feathers (the outermost feathers on the wings) emerge from the second finger so that it and the third finger are covered, but it's very common to reconstruct them without primaries or with the primaries emerging from the wrist or third finger.
- With the 2017 paper that Tyrannosaurus was predominantly scaly, some paleontologists suggest that the other large-bodied coelurosaurs would have had fewer feathering due to their size and bulk. However, some like Therizinosaurus, Deinocheirus, and Yutyrannus would have been special cases in that they lived in temperate environments, with Yutyrannus in particular experiencing cold winters.

T. rex and other Tyrannosaurs

See also: Tyrannosaurus rex

Any time Tyrannosaurus rex is depicted with three functional fingers or more. It had only two functional fingers on each hand. Also, tyrannosaur arms being described as weak — short, yes. Weak, no. This is similar to the condition in other coelurosaurs, which utilized the forelimbs for subduing prey and eventually for flight.
Tyrannosaurus making a loud thud when it walked, when its feet most likely had fatty pads to silence its tread and make it inconspicuous to its intended quarry, since it'd be hard to sneak up on prey when one shakes the earth as they walk.
Tyrannosaurus emitting a mammalian roar. Neither birds nor crocodilians can emit such roars, so tyrannosaurs almost certainly couldn't roar in that sense, either. Although crocodilians (and therefore possibly some dinosaurs) can make a sound that would be reasonably described as a "roar", it doesn't sound anything like something a lion, tiger or bear would give off (It sounds vaguely like an engine revving). And rather than open-mouthed roaring like mammals, T. rex would've more likely emitted vocalizations with the mouth closed, like crocodilians do today, as its hearing was found to have been very sensitive to low-frequency vibrations (the kind used in long-distance communciation) rather than the kind of roars we're familiar with.
Any time T. rex is spelled "T-rex" or some variation thereof (even "T. Rex" isn't techically correct). T. rex is an abbreviation for the scientific name Tyrannosaurus rex, just like E. coli is an abbreviation for Escherichia coli, so the hyphen is not applicable. Scientific names are given with genus capitalized and species not, and are traditionally italicized
T. rex hunting fully-grown giant sauropods. There was a sauropod that coexisted with T. rex over part of its range: Alamosaurus, which mostly lived farther south but overlapped with it in Wyoming and Utah. However, there is no evidence that T. rex preyed on it. Most of its prey, as confirmed in the fossil record, is comprised of hadrosaurs like Edmontosaurus and ceratopsians like Triceratops. Theropods with crushing jaws and puncturing teeth (like T. rex) are more specialized in hunting armored prey. Of course, this doesn't preclude occasional predation of juvenile sauropods, but there's still no direct evidence to support it.
Referring to T. rex as a carnosaur. Before the 1990s, "carnosaur" was a blanket term for any large, hulking theropod, like T. rex, Allosaurus or Albertosaurus. But today, thanks to fossil evidence, we now know that carnosaurs were a distinct group that centered around Allosaurus and its relatives (sometimes called allosauroids instead due to Carnosauria’s historical baggage), and that T. rex was in fact a freakishly large coelurosaur, a member of the same group that includes raptors, ornithomimosaurs, and birds.
Tyrannosaurs (and occasionally other saurischians) with short, box-shaped heads that have a squared-off snout, e.g. Charles R. Knight's famous illustration◊. This is generally very prevalent in animation and illustration, and is good sign that nobody involved bothered to do any research at all, as no known dinosaur had any head that even looked close to this. Similarly, tyrannosaurs are often depicted with heads that are smoothed over on the top, lacking the keratinous crests or bosses they most likely had in real life.
Tyrannosaurs having shallow-rooted teeth. Unlike the teeth of other theropods, which have roots the same length as the crown, tyrannosaur teeth have roots that are twice the length of the crown. This enables tyrannosaurs to grip onto struggling prey and not have their tooth fall out all the time.
Either portraying large-bodied tyrannosaurids as having crocodilian scutes, lizard-like scales, or completely smothering it in a heavy coat of feathers. None of these are correct, thanks to a 2017 paper, which suggested the underside, tail, and legs had miniscule scales, similar to those seen on a bird's feet. The scales are so small that the skin would look naked at a distance, though the facial region probably had thick dermal armour, a feature yet to be incorporated into mainstream culture. Feathers, if present, would have been restricted to the head, neck, and back, with the animal relying on its sheer bulk to withstand seasonal cold, much like the bison of today.
- Some palaeontologists have suggested that baby tyrannosaurs had feathers, but lost them as they grew into adults. However, since feathers are basically highly evolved scales, if that assumption is true, then adult tyrannosaurs would have had bare, scaleless skin rather than scales and would have looked less like dragons than giant plucked chickens.
Tyrannosaurus' vision being based only on movement. This was popularized by Jurassic Park (1993), despite the original novel explaining that the motion-based vision was the result of the frog DNA used to recreate the park dinosaurs. It's actually believed that T. rex had excellent vision, probably better than humans and even that of modern birds of prey like hawks.
Sue is often mistaken as the first T. rex found. It’s the most completely-preserved T. rex but it wasn’t the first. The first one was found 85 years before then.
The oft-stated meme that chickens are the closest living relative of T. rex. Really, Tyrannosaurus isn't any more closely related to chickens than to any other modern bird species. Even worse, that tyrannosaurs evolved into chickens. The group that includes the modern chicken and other fowl (the Galloanseres) were already around at the time, long since diverged from the tyrannosaur line. It should also be noted that, however many feathers a T. rex may or may not have had, it really wouldn't look at all like a chicken or any other bird.
Albertosaurus and Gorgosaurus looking like down-sized adult T. rex, when they were more lightly-built and built for speed. Even in the case of T. rex itself, the juveniles and subadults having the same leg proportions and heavily-built body as the adults is inaccurate. Like Albertosaurus and Gorgosaurus, they should be more lightly built and likely occupied different niches than the fully-grown adults.
A trope especially common in older works was portraying Tyrannosaurus, and sometimes other large carnivorous theropods, as being totally inept in the water. There was never any actual evidence for this very popular paleomeme except perhaps the similarly once-popular notion that the hadrosaurs were water-inclined animals with (supposed) adaptations for swimming. Since Tyrannosaurus didn't have any adaptations for swimming, unlike the contemporary hadrosaurs, this must've meant its otherwise hapless prey must've fled to the water where it couldn't follow to escape it. This of course ignores the fact that plenty of modern animals have no specific adaptations for swimming, but are still capable swimmers (such as, for example, humans). This becomes ironic when you realize T. rex lived in a swamplands habitat, alongside Edmontosaurus and Triceratops, so it would have had to traverse into water.

Dromaeosaurs (Raptors)

Main Page: Raptor Attack

Whenever raptors (aka dromaeosaurids) are depicted as scaly, lizard-eyed dragon men with claws, like this◊ or this◊. This is Science Marches On for works before the late 1990s, but is inexcusable in the 2000s. While it is debatable whether all coelurosaurs (such as T. rex) were feathered, there is no debate about the raptors. And no, raptors were not just Jurassic Park-style scaly monsters that had been tarred and feathered; they had wings, tail-feathers and feathers surrounding their eyes◊. If you saw a dromaeosaur from a distance, or even with its mouth closed, you would mistake it for a large, predatory bird, fitting for a group very closely related to the ancestors of modern birds.
Whenever Velociraptor is depicted as resembling Deinonychus. Deinonychus was a roughly wolf-sized predator that lived in North America, while Velociraptor was a dog-sized lone predator that lived in Mongolia. The confusion is quite deliberate, and can be laid at the feet of two individuals: paleontologist/paleoartist Gregory Paul, who placed them in the same genus (the guy has some fairly idiosyncratic personal views on taxonomy) and Jurassic Park author Michael Crichton, who liked the name Velociraptor so much he didn't care if Paul was literally the only paleontologist on Earth who considered them the same. When creating "Velociraptors" for the first Jurassic Park film, the crew used Deinonychus as a model even as they kept the wrong name in the script(since it sounded cooler and more iconic to them), and one of the most enduring public misconceptions about dinosaurs was born.
The form of the raptor's hands is often shown wrong. While real raptors had hands which paralleled each other and were wing-like in appearance, most raptors in media have paw-like hands, as shown here◊.
Utahraptor being portrayed as an oversized Deinonychus in post-2014 works. Utahraptor is now known to have a bulky body, shorter legs and tail, and procumbent jaws.
Referring to the famous "two-clawed raptor" Balaur bondoc as a dromaeosaur. While it was initially believed to be a very unusual member, notably having only two fingers instead of three, further studies have now reclassified it out of Dromaeosauridae and plonked it right into Avialae, containing modern birds as well as some primitive, toothed avians. Note that both Dromaeosauridae and Avialae are within the broader group Paraves, meaning that despite appearances, Balaur was not actually moved very far on the family tree!
Microraptor gliding with its legs splayed apart, which would have dislocated its joints. Microraptor would have glided with its legs down.

Allosaurus and other Carnosaurs

Allosauroids are sometimes depicted as being able to easily kill completely armored dinosaurs such as ankylosaurs, an impossible feat since they have cutting rather than crushing teeth. This is why tyrannosaurs are more built for attacking armored prey. These two groups are opposite ends of the specialization spectrum; Allosaurus and it's relatives were actually well evolved for hunting the massive sauropods by slashing into them with their teeth and bleeding them to death, monitor lizard-style. It's also been stated in some sources and documentaries that Allosaurus had a bite force weaker than a lion's and thus had to use its head like an axe to slash at prey; not only would this strategy have broken its teeth or outright broken its skull and jaw, but the original study that led to such a claim about its bite strength was based on incomplete data. Allosaurus would not have been able to bite as strongly as T. rex, but its jaw strength was in fact more respectable than previously thought.
Allosaurus used to be depicted looking like a three-fingered, downsized Tyrannosaurus (i.e. bulky body, no brow horns). This was during the age when it was considered to be an ancestor or close cousin of T. rex, which we now know was simply not the case.
In a lot of older media, including documentaries like Walking with Dinosaurs, The Ballad of Big Al, and When Dinosaurs Roamed America, adult Allosaurus are depicted as being comparable in size to T. rex, stretching around 12 meters long, even though most allosaurid specimens from the Morrison Formation are midsized (7.5-9 meters long), while specimens over 10 meters in length are rare, fragmentary and only known from the uppermost strata (implying large size only developed towards the end of their reign), which is something that is pointed out in media like 1988's Predatory Dinosaurs Of The World. There is also debate about whether the larger specimens even belong to Allosaurus and not a related genus, called Saurophaganax (with most later studies favoring the latter).

Spinosaurs in General

Any spinosaurid that is depicted as an entirely terrestrial predator. All evidence of spinosaurid meals found consists of fish, a young plant-eating dinosaur (Iguanodon), and a fish-eating pterosaur (either caught while fishing or scavenged on the shore). As a rule, any theropod with non-serrated teeth is not a sauropod killer, because sauropods require a very specific hunting method. While it is still very likely they could have ambushed other dinosaurs by attacking like a crocodile, killers of sauropods and armored dinosaurs, they were not.
Any spinosaurid with its nostrils at the end of its snout. Spinosaurids have their nostrils farther back on the snout, which helped them breathe as they fished or submerged their jaws in the water.
Giving spinosaurs an alligator-like overbite. Much like crocodiles, spinosaurs had teeth that interlock with each other, and they also had a notch in the toothrow used for trapping fish.
Spinosaurids are usually portrayed without the triangular crest above the eyes. Alternatively, they would have two Allosaurus-like crests, which was invented by Jurassic Park III.
Spinosaurids are sometimes portrayed as quadrupeds, due to their large forelimbs. Like all theropods, they are strictly bipedal as they cannot pronate their hands. It's possible for spinosaurids to crouch in a quadrupedal pose though.

Spinosaurus and other Spinosaurs

Spinosaurus with an allosaur or tyrannosaur-like skull and four-fingered hands. Science Marches On for works from before the late 1980s, but otherwise unacceptable.
Now some new Spinosaurus fossils make everything pre-August 2014 inaccurate. For reference, it had hilariously short legs and was more aquatic than previously thought. Just how short the legs were, however, is unclear. However, some paleontologists have expressed skepticism over this model, suggesting the short-legged fossils might be either chimeras or from a different species. Additionally, the assumption that it was quadrupedal is not based on any definitive evidence. Any and all known information on Spinosaurus is in flux at the time of this writing, but it seems it most likely was semi-aquatic and had short legs albeit still bipedal, since the arms are unable to support constant quadrupedal movement on land since it can't pronate its hands. As of 2020, Spinosaurus now possesses a flat, crocodile-like tail, suggesting it was primarily aquatic, and a 2022 study only solidified it by discoverering that the bones of it were dense, perfect for submerging.
The two crests above Spinosaurus eyes are actually located further front to the snout, and as such some depictions actually have the eyes far too front, in the wrong set of fenestrae!
Portraying Baryonyx without the enlarged claw on its first finger, despite said claw being where the genus got its name from.
- Depicting it as purely a shoreline-hunting predator is this thanks the above-mentioned 2022 study discovered that Baryonyx had dense bones and thus could dive easily.

Carnotaurus and other Ceratosaurs

Carnotaurus (or any other abelisaurid) with tyrannosaur or allosaur-like arms. They had ridiculously small arms that were actually invisible as they lay flush against the body and probably completely useless.
Any time Carnotaurus and Ceratosaurus are shown with a full covering of feathers. Despite the increasing evidence that many (or even most) theropods had feathers, Carnotaurus is the only theropod that we have any definitive proof of no feathering thanks to a really well-preserved fossil with skin impressions. Or at least not on most of its body; a sparsely-feathered Carnotaurus still wouldn't be out of the question. While it's debatable as to whether Ceratosaurus had feathers, it is unlikely to have a full coat due to the presence of osteoderms.
Any time Ceratosaurus is portrayed with only one horn, namely just its trademark nasal horn. Ceratosaurus actually had three horns, including two small ones over each eye. These horns were also fairly laterally-flat and resembled blades, in contrast to the broad horns that befall most depictions.
There seems to be a persistent misconception that Ceratosaurus was outcompeted and driven into extinction by Allosaurus (like in Jurassic Fight Club). This is pretty absurd, since the two taxa are known to have appeared in and disappeared from the Late Jurassic fossil record at around the same time, having coexisted for nearly 10 million years. While Allosaurus would have been the more dominant apex predator (due to its larger size), Ceratosaurus had no issue coexisting alongside it as a mesocarnivore, akin to lions and leopards today. There are many who also suggest that they may have occupied different niches, which kept conflicts minimal.
Similarly, the notion that ceratosaurs as a whole were outcompeted by the more derived tetanurans (like allosaurs). While ceratosaurids proper like Ceratosaurus seem to have vanished by the end of the Jurassic ^note, abelisaurs, which are classed as ceratosaurs, were incredibly successful in the Southern Hemisphere throughout the entirety of the Cretaceous, being found from Argentina to Africa to India, and by the Late Cretaceous, they even colonized Europe (like Arcovenator), all while coexisting with tetanurans like megaraptorans and carcharodontosaurs (the latter being super-sized, derived allosaurs), and actually outlasted the carcharodontosaurs, who vanished around 90 million years ago, while abelisaurs were wiped out during the K-T extinction, 66 million years ago.

Oviraptorosaurs

Egg-stealing Oviraptor. Yes, its name means "egg stealer", and oviraptorosaurs appear to have been omnivorous, but it is unacceptable if eggs are stated to be the main or only source of their diets. The name was chosen in 1924 by Henry Fairfield Osborn, who also named T. rex, after paleontologist/adventurer/possible Indiana Jones inspiration Roy Chapman Andrews discovered Oviraptor near a nest of eggs, but even Osborn felt it might be misleading. Discoveries of related species since then have pretty much confirmed that those eggs were the Oviraptor's, and she/he was likely brooding them, not stealing them. It's certainly possible that oviraptorosaurs sometimes ate eggs, but the model of them as primarily or even outright exclusively egg eaters is thoroughly dead.
Oviraptorosaurs without feathers. They were so heavily feathered that they were essentially indistinguishable from modern birds. They even had beaks.
Oviraptor refers only to a single, poorly preserved specimen unearthed by Roy Chapman Andrews in 1924. Subsequently discovered "Oviraptors" have all eventually been placed in separate genera, usually Khaan, Conchoraptor or Citipati. Restorations of "Oviraptor" tend to be based on these other, less well known dinosaurs.
Thanks to John Sibbick, Avimimus was often portrayed as a flightless clone of Archaeopteryx, namely as a bizarre lizard-bird hybrid complete with a mouth full of teeth. Avimimus actually had a short head with a toothless beak and, like any other oviraptorosaur, was practically identical to modern birds.

Ornithomimosaurs (Ostrich-Dinosaurs)

Featherless ornithomimosaurs. We know ornithomimosaurs were covered in feathers due to many specimens being preserved with them or signs that they had them.
Ornithomimids with teeth. Early ornithomimosaurs such as Pelecanimimus possessed teeth (very tiny teeth), but they were absent in advanced ones.
Ornithomimosaurs running with vertical necks like ostriches. Due to their long tails, ornithomimosaurs held their necks at an angle.
Ornithomimids being exclusively herbivores or carnivores, with older portrayals showing them as egg-eaters. They were actually omnivores, though they leaned to a more herbivorous diet similar to the ratites that they resembled.

Archaeopteryx and other Protobirds

Whether all avialans including Archaeopteryx are birds or not is still not settled; some argue that they are, others argue that birds should only be those avialans classed under either the clade Aves or the upper clade Ornithurae (so that beaked birds that still possess teeth, like Ichthyornis and Hesperonis, wouldn't be left out). Right now the consensus seems to be settling on the latter option, but the argument persists.
Archaeopteryx and many enanthiornithines possessing toothy or toothless beaks. In real life, they had toothy snouts similar to other paravians like dromaeosaurs and troodontids. Having teeth in the beak would be impossible; even in the case of ornithurans that possess both at the same time (e.g. Hesperornis), they don't occupy the same space.
Archaeopteryx is usually depicted being an skilled flyer like its modern relatives, or completely flightless due to being primitive. It is now generally agreed among paleontologists that Archaeopteryx was a poor flyer, but a flyer nonetheless.
Archaeopteryx having generic bird feet with the hallux touching the ground, rather than raptor-like feet including the sickle-shaped claw.
The traditional depiction of Archaeopteryx with multicolored, macaw-like plumage. Thanks to preserved melanosomes, we now know it at the very least had black wingtips.

Birds

Hesperornis being portrayed walking upright like a penguin. Actually, Hesperornis's legs were too weak to support its body on land, therefore it moved on its belly like modern loons.
The flightless bird Gastornis (called "Diatryma" in early works) being portrayed as a carnivore in post-2014 works. Calcium isotopes in the bones of Gastornis have confirmed that it was a herbivore, not to mention it lacks other predatory features such as sharp talons (based on footprints discovered in 2012) or a hooked beak. With that said, treating it as a harmless gentle giant because of this info is also a case of artistic license, as given its large size and powerful beak, and the fact that it would need to defend its young from predators such as terrestrial crocodylomorphs, mesonychids, and creodonts, it was very likely not a bird you would want to mess with, any more so than the equally herbivorous ostrich or cassowary.
Any work that portrays Gastornis with hairy ratite-like feathers. This was based on fossilized fibrous strands which were thought to be Gastornis feathers, but these turned out to have been plant fibers. Gastornis actually had advanced feathers like flying birds, thanks to an actual fossilized feather that most likely belong to it. It should be noted Gastornis is actually more closely related to ducks rather than ostriches.
The dodo is popularly described as stupid; in fact the dodo was a member of the pigeon family, which is noted for its intelligence. The reason it died out was because it had no learned fear of humans and no defence against introduced species, particularly rats.
Any post-2006 work that depicts phorusrhacids (aka, the famous "terror birds") with clawed hands like those of non-avian theropods. This came from the fact that the North American genus Titanis had unusually bent wings that initially suggested this. However, it was pointed out that seriemas, the terror birds' closest living relatives, have similarly bent wings, and still lack wing claws.
Phorusrhacids have traditionally been thought of as a victim in the Great American Interchange being outcompeted by Smilodon when they showed up in South America (as shown on Walking with Beasts for example). This theory has mostly been discarded; they were already on their last legs thanks to environmental pressures and may have already died out by the time Smilodon reached South America. They weren't unsuccessful even then, though - one of the last phorusrhacids, Titanis, coexisted in North America alongside Smilodon and other native predators, and have even been theorized to have prevented such predators from getting bigger until it died out. So not only did Great American Interchange allow the group to hang on for a bit longer, but it would have been the terror birds bullying Smilodon rather than vice versa.
Phorusrhacids are sometimes shown using their beaks to seize and shake small prey to death like a dog. We now know that their skulls weren't strong enough laterally to enable this; instead, the birds would have more likely jabbed and thrust the hooked tips of their beaks into prey and pulled back to gouge into it repeatedly, more like modern hawks or vultures.

Other Theropods

Dilophosaurus is frequently depicted, especially in more inaccurate works, with a frill and venomous spit; the venom was made up by the Jurassic Park novel and the frill by The Film of the Book, with absolutely no evidence for either. The venom hypothesis was proposed because Dilophosaurus was once depicted as being slender and graceful, with a jaw too weak for conventional attack (hence the claims by some scientists that it had to rely on other hunting methods, such as venom); new findings in 2020 have since shown that it was a more robust animal with stronger jaws than traditionally portrayed, and its crests were reinforced by a system of air sacs and could have been used for resonating, much like those of hadrosaurs.
Ornitholestes with a crest or horn on its nose. This stemmed from the fact that the type skeleton of Ornitholestes had its nasal bones broken off and the area there seemingly points upwards, which turned out to be a result of the bones being flattened during fossilization.
Therizinosaurs lacking cheeks. Therizinosaur skulls were similar to those of ornithischians, namely having a toothless beak and inset teeth for chewing plants, making cheeks or similar structures more plausible. That said, what the tissues around the mouths of most plant-eating dinosaurs would have looked like is still hotly debated.
Old portraits would show Megalosaurus preying on Iguanodon in the Early Cretaceous, despite the former being from the Middle Jurassic. This was because the two genera were discovered in England, and many theropod specimens dating to the Early Cretaceous were originally assigned to Megalosaurus. This becomes a case of Accidentally Correct Zoology with the discovery and naming of Neovenator, a large carnosaur that was a contemporary of Iguanodon. Not to mention the also contemporary Baryonyx turned out to be more closely related to Megalosaurus than to any allosauroid.
Megaraptor as a dromaeosaurid in post-2003 works, as we now know its distinctive enlarged claws are actually from the hand rather than the foot.

Sauropods in General

Whenever sauropods are depicted up to their necks in water. This is more commonly seen in older depictions, because paleontologists initially couldn't believe that such huge creatures could exist without being supported in water. However, we now know that sauropods could not breathe in such a situation (as the water pressure would crush their lungs), and so it is thankfully a slowly dying trope. In fact, studies on the flotation dynamics of sauropods show that they would have floated unsteadily on the water surface rather than walk along the bottom were they to take a dip beyond wading depth. That said, that doesn't mean sauropods did not hang around in water occasionally, similar to elephants and moose.
As mentioned above, the very belief that sauropods were too heavy to exist on land. We now know sauropods have light yet powerful skeletons with air-filled chambers, which allowed them to grow to such a large size while stabilizing their weight.
Sauropods chewing their food. They couldn't; they didn't have cheeks or chewing molars. In fact, their long necks were only possible because they didn't need to chew- no chewing means no big jaw muscles, ergo small, light head, ergo long neck. On that note, the idea that sauropods had to swallow rocks to aid in digestion is flawed as of late, since gastrolith fossils are rare. It's now believed sauropods just used their very large guts to slowly digest vegetation.
Sauropods having their nostrils on the top of their heads. This is because of their nasal openings being positioned on the apex of the skull, which led to the idea that the nostrils were placed there and thus were used as snorkels or to help them breathe as they ate. We now know the nostrils were placed lower down near the tip of the snout.
Sauropods with elephant feet. In actuality, most had one visible claw on each front foot, and three claws on each hind foot. Some, like the titanosaurs, had clawless front feet which looked more like stumps than anything else.
Sauropods having skinnier, more flexible necks than in real life; the vertebrae were actually locked together somewhat to support the weight of the neck, which probably had a lot of muscle just to hold itself up. Similarly, sauropods are sometimes depicted holding their necks in a completely vertical pose. This is incorrect, but whether they held their necks at an incline or more or less horizontally is uncertain.
Sauropods singing like whales is unlikely for the same reasons as T. rex roaring like a lion is: lacking the vocal organs needed for mammal-like vocalizations. They would have more likely communicated through low-frequency vibrations traveling through the ground and picked up by the feet, like elephants do, or possibly by lashing their tails to create miniature sonic booms in the case of the whip-tailed diplodocids.
Sauropods are commonly depicted having either grins with their teeth sticking out or fleshy, pliable lips. In 2017 it was discovered that their teeth were covered over by gums which in turn would have been covered by a keratinous sheath forming into a beak (or more accurately a pseudo-beak, since there's still teeth).

Brontosaurus

Confusing Brontosaurus with Apatosaurus. Before 2015, people were most likely to call an Apatosaurus a Brontosaurus; however, these days it could just as easily be the other way around. Up until 2015, anyone remotely versed in palaeontology would have told you that the word Brontosaurus had as much scientific meaning as the word "unicorn", since the creature never existed. Rather, the name, meaning "thunder lizard", was given to a misidentified older specimen of Apatosaurus. Why and how the word "Brontosaurus" survived is too complicated to explain quickly (in essence, big egos), but regardless, the Rule of Cool knows no statute of limitations, and the Thunder Lizard persisted to this day. And it turned out that was lucky, because in 2015 studies of Brontosaurus skeletons led scientists to conclude that yes, Brontosaurus was its own genus after all, and so the name was brought back from legend into natural history. It's still wrong to use it for all sauropods though.
As noted in the comic books section below, the common story about Brontosaurus being just an Apatosaurus reconstructed with Camarasaurus-like head was in fact incorrect even before 2015 revision of Apatosaurus, as the synonymization of Brontosaurus with Apatosaurus was an issue unrelated to the original incorrect restoration of Brontosaurus excelsus. Also, even when both genera were synonymized, their type species Apatosaurus ajax and Apatosaurus/Brontosaurus excelsus were retained as distinct species; just because they were classified in the same genus for a while doesn't mean they were the same animal - just like, say, assigning lions, tigers, jaguars and leopards to the single genus Panthera doesn't mean they are all the same animal.
Any time Brontosaurus or Apatosaurus are portrayed with longer, thinner necks and more lightly-built frames than in real life. Apatosaurine sauropods are known for having a heavy build with very thick necks. And because the necks were so robust they might have been used for fighting, and the placement of the cervical ribs suggest the presence of thickened pads or keratinous spikes.

Other Sauropods

As noted above, referring to any sauropod as a Brontosaurus or even an Apatosaurus, unless, of course, it actually is one. Brachiosaurus and Diplodocus are both common victims of this.
Brachiosaurus with a diplodocid-like body. Brachiosaurids (or at least those for which forelimbs & tails are known) have longer forearms and shorter tails. In fact, Brachiosaurus got its name ("arm reptile") for having longer forelimbs than hindlimbs.
Similarly, titanosaurs like Argentinosaurus or Alamosaurus resembling Diplodocus rather than having a high-crested skull and longer forelimbs like Brachiosaurus.
Diplodocids with shorter tails like that of a brachiosaurid. Their tails were actually very long and whip-like.
Brachiosaurids being able to rear up on their hind legs like other sauropods is unlikely, because their center of gravity was too far from their hips (due to their aforementioned longer forearms and shorter tails). It was also probably unnecessary, because the increase in height they'd gain from it would be minimal compared to other sauropods.
Amargasaurus has been traditionally portrayed with two parallel sails, due to its distinctive neck spines resembling those of sail-backed pelycosaurs such as Dimetrodon. This hypothesis was not considered likely, since the spines are rounded rather than flattened, there was little space between them, and possessing sails would limit neck movement. Instead Amargasaurus's spines would have been solitary structures sheathed in keratin, making them effective for display and combat. However, a 2022 paper challenged this notion and suggested that sails would have been likely after all, since the spines show cylical growth marks. That said, the sails would probably have resembled humps rather than fins as in traditional depictions.
Mamenchisaurus with a Diplodocus-like skull rather than short and boxy like Camarasaurus and with no tail club. It was originally considered a close relative of Diplodocus, but its affinities with other Chinese sauropods were recognized by the mid-1990s.
Agustinia being depicted with stegosaur-like spikes protruding from down its back. It's very likely that these spikes were actually, in fact broken ribs, strongly suggesting that Agustinia would have probably looked more like pretty much every other sauropod.

Other Saurischians

Unless it's a case of Science Marches On, core prosauropods like Plateosaurus being mainly quadrupedal or being able to walk on all fours at all is inaccurate. They were obligate bipeds, although the juveniles of some species appear to have been quadrupedal.
While adult skeletons haven't been discovered yet, it's unlikely adult Mussaurus would have been short-necked and quadrupedal like the juveniles rather than long-necked and bipedal like other adult plateosaurids.
There have been debates as to whether Eoraptor and herrerasaurs are really theropods rather than either sauropodomorphs or basal saurischians. Recent studies suggest they are not theropods, with Eoraptor being a sauropodomorph and herrerasaurs being ambiguous.

Ornithischians

Ornithischians in General

Ornithischians having lizard-like mouths, with lips instead of a beak and no cheek-flaps. Since ornithischians are characterized by having chewing teeth, they must have flaps of skin on the sides of the mouth like most other reptiles to keep food from falling out. That said, they probably didn't have muscled cheeks like mammals do, either, since that would require a lot of rearrangement of the facial muscles for no viable purpose.
It used to be common practice to label all bipedal ornithischians as ornithopods, but this is no longer applicable. Hypsilophodon and its close relatives were likely very basal ornithischians without any ties to specific groups, pachycephalosaurs are most closely related to ceratopsians, and the fang-bearing heterodontosaurs have since been found to be very primitive pachycephalosaurs themselves.

Stegosaurs in General

It's often believed that stegosaurs were strictly low-browsers due to their small heads and shorter forelimbs. This disregards the fact stegosaurs are able to rear up on their hind legs, since their center of gravity is placed back in their hips.
Stegosaurs being depicted with a toothy lizard-like mouth. In reality, stegosaurs had beaks at the end of the snout, though it's unsure whether they had cheek flaps or exposed muscles on the sides of the mouth.
Concerning stegosaurid plate function:
- A commonly stated "fact" is that nobody knows what the distinctive back plates of stegosaurs were used for. The consensus nowadays is that because they came in a variety of shapes and sizes from species to species, they most likely evolved precisely to be distinctive (i.e. species recognition) and to appear attractive to potential mates or intimidating to rivals.
- It's been established that the plates of stegosaurs were covered in horny sheaths, based on well-preserved tissues on the plates of Hesperosaurus, which would make the portrayals of Stegosaurus with skin-covered plates unlikely. This would also mean the plates could not have turned red by flushing blood, as Walking with Dinosaurs demonstrated, though seeing as stegosaurid plates likely evolved for the sake of display and species recognition, they could've been brightly colored like the beaks of toucans at least during the breeding season (so they probably weren't dull-colored as commonly portrayed in fiction).
- The notion that Stegosaurus itself used its plates for thermoregulation is somewhat more excusable, since the horn-covered scutes of modern alligators are capable of such due to containing plenty of blood vessels not unlike what Stegosaurus plates would have had (as the plenty of grooves in the fossilized bone cores would indicate). However, this function was likely not as pertinent as is sometimes stated, especially since most other stegosaurs had much smaller plates or a mix of plates and spikes on their backs which wouldn't have provided as much surface area for absorbing or losing heat.
- Also, stegosaurs using their plates as armor. While some studies suggest the plates were covered in horn, they are still irregularly placed for protection and keep the animal's sides unprotected. Instead, stegosaurs more likely used the chainmail-like scutes underneath their skin as protection against predators, though the plates may have impeded a predator from attacking the stegosaur's back or leaping onto it (not to mention that some stegosaurs like Kentrosaurus had plates and spikes protruding from the dorsal area, albeit with the latter usually ranging from halfway down the spine to the end of the tail).

Stegosaurus

No, Stegosaurus didn't have a walnut-sized brain. This assertion was first stated in 1945 by paleontologist Edwin Colbert, and caught on due to the then-common notion of dinosaurs being ill-fit for survival; in reality, Stegosaurus' brain would have been the same size relative to its body as most other reptiles. In a similar vein, the notion that it had a second brain in its hip is also false - this idea stems from 19th-century Yale paleontologist Othniel Charles Marsh, who described an expanded neural canal in both Stegosaurus and Camarasaurus. Simply put, a cluster of nerves does not a brain make, and for that matter, there is no vertebrate (as far as we know, anyway) which has or needs more than one brain (more recent research indicates that there was probably no nerve cluster in this hip cavity anyway, as the same gap is known in modern birds and it stores fatty tissue).
The plates of Stegosaurus were arranged alternatively in real life, but good luck seeing a portrayal with this arrangement. Usually the plates would be paired or even arranged in a single row (although the latter would be fairly closer to the real arrangement). Said plates will also be misshapen, often as triangles or half-circles as opposed to pentagonal. There's even at least one very old depiction of Stegosaurus being covered in bony plates resembling pangolin scales, though that was before more complete fossils showed that the spikes stuck straight up from the back. The dermal armor of Stegosaurus in fact consisted of much, much smaller and more numerous nodules of bone like a built-in suit of chainmail, especially around the otherwise vulnerable throat area, but don't expect this to be shown in fiction outside of documentaries.
Any time Stegosaurus is portrayed with the wrong number of tail spikes, from lacking any to having up to eight. Said tail spikes may also be too short, when the fossil spikes shown they were at least 60-90 cm (2 to 3 feet) long^note.
Any depiction of Stegosaurus that has a fat body, a dragging tail, a stubby neck, and splayed limbs. This is excusable if this is seen in older portraits, but not in modern ones.
Stegosaurus with an unrealistically long neck. While its neck wasn't exactly short (according to a young adult named "Sophie", which is the most complete specimen to date), it was far from the sauropod-like necks some depictions portray it with. Although Miragaia, a long-necked stegosaur, was discovered in 2009.
Any time Stegosaurus is portrayed as being too slow and sluggish to defend itself from predators. Stegosaurs have front legs shorter than their back legs; while this limited their speed, it put the center of gravity in their hips. This enabled stegosaurs to rapidly turn their bodies around, giving them opportunity to strike predators with their tails and keep them away from their weak spots. It helps that Stegosaurus lived alongside swift, fleet-footed predators such as Allosaurus, so maneuverability would have been necessary for its defensive mechanism to be more effective in spite of its size and bulk.
Stegosaurus having feet like an elephant or a rhino. In real life, stegosaurs have five toes on each forefoot, four of which being slightly long (though only two possess claws) while the fifth is hidden underneath the skin, and three short toes on each hindfoot.
Depictions of Stegosaurus with the thagomizer spikes facing upward, while they more likely faced horizontally, a position that would have made them far easier to use as an offensive weapon.

Other Stegosaurs

Anytime Kentrosaurus is depicted without its shoulder spikes.
Wuerhosaurus is traditionally depicted with low, rounded plates due to the way its only known fossil plate is shaped, but it is now acknowledged that said plate is actually broken. Their actual shape is unknown.
Dacentrurus is often stated to be small stegosaur. In reality, according to a 5-foot-wide pelvis, it was actually one of the largest stegosaurs and even rivaled Stegosaurus in size.
Similar to the above, Kentrosaurus will often be depicted as being almost the same size as Stegosaurus, when it was a small stegosaur in reality.

Ankylosaurs

Ankylosaur armor is almost always depicted being a shell, when in reality it was fused into the body. In fact, Ankylosaurus means "Fused reptile" because of this feature. Ankylosaurids also had armor plates or half-rings covering the neck.
Any portrayal of Ankylosaurus that is lacking its squamosal horns (the two horns that point backwards from the back of its head) and jugal horns (the two other horns below that point downwards and back).
Anytime Ankylosaurus is depicted with spiky osteoderms, with big spikes protruding along its sides (a strictly nodosaur trait). Ankylosaurus actually had flat osteoderms, with slightly elongated ones being from along the sides of the half-rings, hips and tail. The side spikes were due to associating the armor with that of the nodosaur Edmontonia, which was erroneously depicted with a tail club. There were ankylosaurids that resembled this portrayal, such as Tarchia, only the "side spikes" are still placed higher than on a nodosaur.
Club-tailed ankylosaurs are sometimes depicted with flexible tails capable of curving all the way down their length. In reality, the back half of this type of tail was stiffened by rods of bone, functioning like the handle of a hammer so the club could strike more forcefully. The tail club of Ankylosaurus itself will often also be incorrectly shaped, either two-lobed like on Euoplocephalus or having spikes protruding from it like a mace - it's actually three tightly fused knobs of bone, shaped like this◊.
Confusing Ankylosaurus with Euoplocephalus. Besides having smoothed armor compared to Euoplocephalus, Ankylosaurus also had sideways-facing nostrils unique to other ankylosaurids.
The old-fashioned portrayal of Scolosaurus (and in some cases, Euoplocephalus) with a nose horn and two spikes pronging from the tail club. This is now a dead trope, since we now know Scolosaurus would have been identical to Euoplocephalus (which it was formerly synonymous with until 2013, because they were that similar) albeit with longer horns that face downwards. The spikes that were once shown on the tail club actually protruded from around halfway down the tail.
As with other quadrupedal dinosaurs in fiction, ankylosaurs are common victims of the elephant-feet syndrome. They actually had fairly long toes, with three claws on the five toes of the forefoot.
Some depictions of ankylosaurs give them the ability to curl up into a ball like some species of armadillos. Ankylosaurs (and ornithodirans more generally) simply could not do this because their torsos are too vertically stiff, to say nothing of the gastralia (belly ribs) further limiting such flexibility.
Polacanthus was traditionally depicted as some sort of "reverse stegosaur", with a double row of spikes on its back and a double row of plates along its tail. We now know these spikes and plates protruded sidewards, and its armor was also extensive like any other ankylosaur.
Baby ankylosaurs looking like miniature versions of the adults. Ankylosaurs started off having very few to no osteoderms, and the tail club would have grown in at a later stage in life.

Other Thyreophoreans (Armored Dinosaurs)

Both ankylosaurs and stegosaurs used to be portrayed as having hind legs much longer than the front legs, with a downward-curving spine from the hips forward. Recent findings show that the front and back limbs are about the same length, with the spine being relatively straight.
Primitive thyreophoreans such as Scutellosaurus and Scelidosaurus being portrayed as being quadrupedal, which is common in older works. A trackway from Poland shows a similar animal walking in a bipedal manner, hinting that Scelidosaurus may have been more proficient at bipedalism than previously thought, although the precise extent is debatable.
Assuming all thyreophoreans have weapons on the ends of the tails. Some, such as scelidosaurs and nodosaurs, lacked such a feature. It's also been suggested that weaponized tails on stegosaurs and ankylosaurs could only have happened BECAUSE they were armored, since the stiffening of the torso to support the armor was needed to brace the body against the force of swinging a tail weapon.

Marginocephalians (Ceratopsians and Pachycephalosaurs)

Triceratops with a gigantic frill. While it possessed one of the largest skulls of any land animal, its frill was relatively short especially by the likes of Chasmosaurus or Pentaceratops.
Styracosaurus with no frill and the long spikes protruding from the nape. And to a lesser extent, it may be depicted with long, Triceratops-like brow horns (there was a ceratopsian that sort of looked like that—Medusaceratops—but don't expect to see it even in a documentary).
Ceratopsians are often victims of being confused for other ceratopsians. This often includes putting whatever head on to whatever body and calling it whatever (usually Triceratops) or just giving it a completely made up and inaccurate skull because it would look cooler. Some examples include the aforementioned Styracosaurus-with-Triceratops-brow-horns, Triceratops itself having a long Styracosaurus-like nose horn rather than the much shorter one it had in reality, and Pachyrhinosaurus with a horn on its nose despite this genus being known for lacking one.
Ceratopsians did not look the same throughout their lives, we once thought this but thanks to new discoveries, we now know their heads generally changed over the course of of their lives. In fact some are debating whether ceratopsians like Triceratops and Torosaurus were the same species.
It has been said that ceratopsian horns were not used for combat as they were too brittle and might not have been pointed enough to gore through flesh, plus they might not have been able to charge into its opponents as the skull would break upon impact. These both conflict with the fact that when the animal was alive the skull would have been reinforced by strengthening tissues and the horns would have also a layer of keratin, better shaping them for combat and preventing bone breakage.
Basal ceratopsians with no quills or feathers. In Real Life, they had a lot of quill-like integument on the tail, particularly Psittacosaurus which was preserved with them. It is debatable whether the advanced ceratopsians have them, though.
Big ceratopsids having feet like rhinos, hippos, and elephants. In actuality, they had four long toes on each hindfoot, one of which dangles uselessly, and five on each front foot, two of which don't support the weight and lacking claws, either.
Older works have ceratopsians lacking visible beaks, instead having long lizard-like toothy mouths with a beak-shaped tip. In fact, ceratopsians almost certainly had keratin-covered beaks on the end of the snout, though as previously noted, whether or not they had cheek flaps or exposed muscle on the sides of the mouths like most modern reptiles is debatable.
A mummified specimen of Triceratops has shown it had crocodile-like dermal scutes and underbelly, rather than the smooth skin shown in most portraits.
Similarly to ceratopsians, pachycephalosaurs didn't look the same throughout their entire lives. Hatchlings had flat, if somewhat knobby heads, growing domes as they aged. Also like the Triceratops-Torosaurus debate, it's debatable if Dracorex and Stygimoloch weren't the growth stages of Pachycephalosaurus.
Whether pachycephalosaurs used their heads to ram into each other like bighorn sheep, employed them as defensive weapons, etc. is debatable. It's often stated that the dome-shaped skull caps would have glanced off each other, and some claim that they were used for display instead, but many pachycephalosaur skulls show evidence of head trauma, so this hypothesis can't be ruled out just yet. That said, using them against predators every single time is unlikely - many modern animals with defensive headgear like goats and antelopes prefer to flee most of the time, and unless you have the size and muscle to back it up, charging head-first at a predator is generally not a good idea.
Pachycephalosaurus is sometimes portrayed as inaccurately sized, either shrunken down or scaled up almost to the size of large theropods. Its average height is actually about the same as a human at the hip◊.

Hadrosaurs

Hadrosaurs with visible fingers that may or may not be webbed for swimming. Their fingers were actually embedded underneath skin, bounded into a single thickened hoof built for walking on dry land, with nails on two fingers (a hoof-like one on the second finger and a spade-like one on the first) and no thumbs.
No, hadrosaurs were not aquatic animals. They are especially hit with this misconception because the hadrosaur Edmontosaurus has a superficially ducklike skull◊ (hence the nickname "duckbilled dinosaurs"), which lead to the assumption that they ate aquatic plants; some hadrosaur mummies appear to have webbed feet and tails capable of crocodile-like sculling, but as noted above, this was not the case in real life; they were land animals like modern camels or bison. The feet are actually short and compact, almost like hooves, while the tail itself was stiffened by ossified ligaments and incapable of flexing with enough strength to propel them through the water (though one very well-preserved Edmontosaurus mummy shows that they had much larger tail muscles than expected... except that they were used to move the legs, not the tail itself). When they did have to swim, they wouldn't have been any more capable at it than modern hoofed grazers, though this doesn't preclude some wetlands-dwelling ones (including Edmontosaurus itself) taking to the water regardless, a la modern moose.
Assuming hadrosaurs had weak teeth that fell out easily. They had thousands of specialized grinding teeth making up tightly-packed dental batteries that were continuously replaced, arguably one of the most sophisticated chewing mechanisms of any known animals.
Hadrosaurs (or similar ornithopods such as Iguanodon) being perpetually bipedal. Hadrosaurs have stronger forelimbs and weaker hind legs, forcing them to walk mainly on all fours. They would only become bipedal when rearing up or running. However, there are some large ornithopods which probably would have been mainly bipedal, like Mantellisaurus ^note, Camptosaurus and Muttaburasaurus ^note.
Hadrosaurs being too weak to defend themselves from predators. This is due to the misconception that if dinosaurs have horns, sharp teeth, claws, tail clubs, or spikes then they are guaranteed to be dangerous, and hadrosaurs have none of those things. But given that large ornithopods have massive bodies and large tails, it would be hard to imagine they would be defenseless in real life. It's also sometimes stated that hadrosaurs were too slow to escape their enemies, but recent findings have shown that their leg strength and top speed were actually much greater than previously thought.
Related to the above inaccuracy, hadrosaurs being drawn with skinnier bodies than they would have had in real life; they would have most likely needed as much supportive bulk as modern cattle or buffalo of comparable size, and the aforementioned Edmontosaurus mummy suggests large tail and rear leg muscles that would've only added to that. It's also common to depict hadrosaurs as being smaller than their carnivorous contemporaries, but some genera such as Shantungusaurus were in fact some of the largest ornithischian dinosaurs ever discovered, even reaching sizes comparable to some sauropods.
Tsintaosaurus having a unicorn's horn-like crest in post-2013 works. We now know its crest pointed backwards and had rhomboid facets on the upper part.
Lambeosaurus being described as 15m long and the largest hadrosaur. What was once thought to have been a species of Lambeosaurus had been renamed to Magnapaulia, which is now thought to have been 12m long rather than 15. The two valid species of the former, L. lambei and L. magnucristatus are "only" 9-10m long, the same size as most hadrosaur.
Hadrosaurs being portrayed with a literal duckbill. In actuality, this was only the shape of the hard bone, and there was a curved beak made of keratin that covered up the broad duckbill-shape so that it actually looked like this◊.

Other Ornithopods

Tree-climbing Hypsilophodon. This is a discredited hypothesis based on a foot fossil where the first toe seems to be facing backwards like a perching bird's, which was interpreted as being useful for climbing◊. The fossil was actually damaged, and in life the animal was strictly ground-bound with all of the toes on each foot pointed forward◊ ^note.
Iguanodon is sometimes stated to be a cosmopolitan (worldwide) genus (as in Walking with Dinosaurs). This is due to the practice of wastebasket taxonomy, wherein specimens similar to a known taxon are lumped into it (which was common in early palaeontology). Nowadays the only species identified as belonging to the Iguanodon genus are I. bernissartensis of Belgium and I. galvensis of Spain, with many other species once called Iguanodon having been reassigned to other genera.
Iguanodon being depicted as a medium-sized dinosaur. It actually rivaled T. rex in size.
Showing Iguanodon without the enlarged thumb spike on its front limbs, which was likely used both for defense against predators and in intraspecific competition. This is largely fueled by the common misnomer that ornithopods were helpless prey items. Though its later relatives, the hadrosaurs, did not sport such a feature.

Pterosaurs

Marine Reptiles

Marine Reptiles in General

Plesiosaurs, ichthyosaurs and mosasaurs being cold-blooded. They were warm-blooded like whales, great white sharks, and leatherback sea turtles.
Plesiosaurs or any other marine reptiles coming onto land to lay eggs, as we now know they would die if they tried this and instead gave live birth, probably practicing parental care.

Plesiosaurs

Plesiosaurs almost always have bendy necks. In some old books, they are even described as "snake-like". In reality, their necks were relatively stiff and had limited mobility, though they were far from being ramrod-straight.
In a similar vein to the mosasaurs below, it's becoming increasingly likely that plesiosaurs had tail fins due to the way their caudal neural spines are shaped, in contrast with the tapering tails they are commonly portrayed with. Alternately, they might have had whale-like flukes used in steering and balance.
Liopleurodon, thanks to Walking with Dinosaurs, is often thought to be bigger than it actually was; it was 7 meters long rather than 25. The biggest pliosaur we know about was Pliosaurus funkei (aka "Predator X"), which was 13 meters at best. The Liopleurodon in "Walking With Dinosaurs" was based on the "Monster of Aramberri", a very incomplete specimen found in Mexico in 1985; early reports had suggested that it was a juvenile and 18 m in length, leading to speculation of how big it could get as an adult. Despite being initially identified as a Liopleurodon, the Monster has since lost that designation and is currently unclassified. A giant pliosaur vertebra was also reported but turned out to be from a sauropod. Kronosaurus was also oversized for a long time due to being reconstructed with too many vertebrae.
Long-necked plesiosaurs raising their necks above the water is anatomically impossible. The notion that they did this to strike at fish from above like snakes is also unlikely, since their eyes were on top of their heads, which would prevent them from aiming properly if they hunted this way. The long neck most likely evolved to get the relatively small head within striking distance of schools of fish without the large body being noticed.
In some works, plesiosaurs may lunge their heads out of the water to snatch prey from the shore. This is at least plausible in the case of pliosaurs, which had large and powerful jaws and strong necks built to tackle large prey, but unlikely for the long-necked plesiosaurs, which typically fed on much smaller prey and never developed any such adaptations.

Mosasaurs

Mosasaurs with dorsal fringes or crocodilian armor. The dorsal fringes were due to misidentification of tracheal cartilages preserved on mosasaur fossils, while crocodile-like armor is entirely a Rule of Cool invention that has never been supported by fossil evidence (misinterpreted or otherwise). Mosasaurs actually had streamlined bodies, with small overlapping scales similar to on a snake. Also, a well-preserved specimen of Platecarpus revealed that advanced mosasaurs had tail flukes, and therefore swam in a shark-like manner rather than eel-like as traditionally portrayed.
Mosasaurs without forked tongues. Mosasaurs had paired fenestrae in their palates similar to a monitor lizard, which strongly suggest the presence of a forked tongue.
Mosasaurs depicted without palatal teeth◊ (a second smaller set of teeth on their top jaw behind the normal set, so that they would have had three sets in total). It's also very likely that the teeth wouldn't have been visible when the mouth was closed, similar to modern snakes or lizards.

Pseudosuchians

Crocodilians & Other Pseudosuchians

Crocodilians are not descended from dinosaurs. While closely related to true dinosaurs, crocodylomorphs (including extant crocodilians) are in fact a different type of archosaur. The group they belong in is called Pseudosuchia, and includes all archosaurs more closely related to them than to dinosaurs (and by extension, modern birds).
People often think crocodiles and alligators appeared at the same time as Mesozoic dinosaurs, but they didn’t. It is true that crocodyliforms existed for about as long as the dinosaurs have, and that similar looking relatives to today's crocodiles and alligators, like Sarcosuchus or Deinosuchus, lived alongside them and filled the same niches, but the crocodilians we see today didn’t appear until the beginning of the Late Cretaceous.
Depicting all crocodilians as semi-aquatic predators. Pseudosuchians, and crocodyliforms by extension, were an extremely diverse group, and were just as diverse as dinosaurs. There were semi-aquatic ones like modern crocodilians, but also entirely terrestrial predators, terrestrial herbivores, and even filter feeders.
Assuming all pseudosuchians were obligate quadrupeds. Some such as Postosuchus were actually bipedal or at least semi-bipedal - Postosuchus itself had shorter forelimbs and small hands, and was a pursuit predator (rather than a slow-moving ambush predator as Walking with Dinosaurs portrayed), so standing on two legs would be better for bursts of speed. In fact, a good number of early pseudosuchians were similarly bipedal - if you compared the skeleton of such a pseudosuchian with a dinosaur from the same time period, it wouldn't be difficult to confuse the two.
It's sometimes stated that dinosaurs outcompeted crocodyliforms to the extent that the latter group was almost as suppressed as mammals. Pseudosuchians in fact remained relatively successful even after the Triassic/Jurassic extinction wiped out all the large dominant ones known from before then - the infamous Boar-Croc, Kaprosuchus, is one such example, being a terrestrial mid-sized hunter occupying the same role as similarly sized theropods elsewhere. Just because the dinosaurs overtook the roles of the large crocodyliforms didn't mean they upstaged all their ecological niches.

Fish

Megalodon Shark

No, megalodons were not a hundred feet long. Since the only fossils we have of them are their, admittedly big, teeth, reconstructions of megalodon have varied wildly in both size and shape over the years, but most palaeontologists agree that megalodons probably were between 45 and 60 feet long. Additionally, whether or not megalodon is a great white relative is also in dispute, so its common depiction as a giant great white is likely, if not wrong, than at least partially inaccurate. Some have argued that, due to its larger size, megalodon may have required a different body form and likely more resembled a whale shark or basking shark than a white◊. However, a 2024 study suggests that megalodon would have had a longer, more slender body.
Megalodons did not eat dinosaurs (unless you count seabirds). They're actually a relatively recent species, evolving about 23 million years ago and only dying out about 2.6 million years ago, meaning our hominid ancestors just missed them.
Despite what sensational fiction or media hoaxes may tell you, no one has found even the tiniest shred of evidence that megalodons are still alive. In fact, since megalodon preyed on whales, the super-giant cetaceans like blue whales would never have evolved if it hadn't gone extinct. The baleen whales that co-existed with the megalodon were relatively smaller and faster than modern whales, the better to avoid being preyed on.
Any time "megalodon" is spelled as capitalized ("Megalodon" or even "Megalodon"). It's commonly thought to be a genus name, but is actually a species name (the full scientific name is Otodus megalodon).

Other Fish

Helicoprion is often seen by many as one of the most bizarre prehistoric sharks of all time. But it didn’t actually look like that. It was actually more subdued in its appearance.◊ It also wasn’t a shark, but a member of an extinct order whose closest living relatives are ratfish.
Leedsicthys has likewise been depicted with exposed bone plates on its head, with said head having a sloped shape◊. It's believed that Leedsicthys had an elongated, smooth head.◊ And contrary to what some sources say, it did not grow more than 16 meters long.
Dunkleosteus and similar placoderms being portrayed with actual teeth. They were actually toothless, instead having blade-like bone plates forming a beak-like structure.
The traditional depiction of Dunkleosteus with a long, thin body has been put into doubt by 2023 studies, which suggest it had a shorter, more compact body.

Synapsids

Early Synapsids in General

There is some confusion about what actually classifies a synapsid.
- Some use "synapsid" to describe only the early ones like Dimetrodon. In reality this term also includes mammals of today like us.
- The name "mammal-like reptiles" isn’t an accurate description of early synapsids. This term was once in wide use, as the term "reptile" was used to refer to any amniote (land vertebrate that either lays hard-shelled eggs or gives live birth) outside of mammals and birds (in addition to fossil taxa closer to amniotes than to modern amphibians), but in modern nomenclature paleontologists prefer to define taxonomic groups based on phylogeny (evolutionary relationships) rather than phenetics (superficial similarities). Under modern phylogenetic definitions, "reptile" is only used to refer to modern reptiles (lepidosaurs^note, turtles, and crocodylians) and the animals more closely related to them than to mammals, thus synapsids of any kind are no longer considered to be reptiles. A more accurate term for non-mammalian synapsids would be stem-mammals or proto-mammals. However "mammal-like reptile" is still used in some circles.
Any time early synapsids are shown with dinosaur or reptile anatomy and lacking the more mammal like features. Dimetrodon suffers heavily from this, often being shown as just a lizard with a sail on it’s back. A real Dimetrodon (and other basal synapsids) might have had naked skin like a mammal's coupled with pseudo-scales (of a completely different structure than those of true reptiles) on the underside.
In 2012, neural spines of Dimetrodon were reported to be commmonly bent at the tips, indicating that the tips may have been exposed. As such, it became a bit of a paleoart meme to depict Dimetrodon as having only half a sail. However, what the study had actually concluded was that while the extreme tips of the spines indeed were exposed, the rest of the spines (about nine-tenths of it) were covered in a sail, and such would have looked much more like the traditional depiction.
Synapsids being depicted with scaly skin like a lizard or crocodile. While it's debatable what body covering they had, it's unlikely that they had osteoderms. A preseved specimen of the skin impressions of Estemmenosuchus (a strange therapsid resembling a cross of a hippo and a moose) revealed it to have smooth leathery skin, covered in pores that may have housed skin glands similar to mammals of today. (However, it's unclear whether this trait was common on all therapsids, or if others indeed had hair and Estemmenosuchus secondarily lost its fur.)
Early synapsids being shown living alongside dinosaurs like T. rex. While the mammals of course survived, a lot of the earlier synapsids at best only made it to the Triassic, like the dicynodonts, and didn’t live alongside the dinosaurs of the Jurassic and Cretaceous. The few stem-mammal groups that did survive past the end of the Triassic (tritylodontids, tritheledontids, docodonts) are unheard of in fiction and probably would have been more or less indistinguishable to a layman from a true mammal.
Gorgonopsids are always portrayed as having their sabers exposed, despite having huge jaw extensions which their teeth fit inside, suggesting they kept their sabers hidden inside their mouths.
Lystrosaurus and other dicynodonts depicted with the proeminent parts of their skulls being seen along their heads, akin to a ridge. Since such areas served as attachment for neck muscles, it is probable they wouldn't have been visible in the living animals, or at least not as noticeably as in some portrayals.

Mammals in General

Any medium (including a few documentaries) that suggests that mammals either didn't evolve until after dinosaurs died out or had barely done so when they did. In fact, mammals coexisted with the dinosaurs throughout most of the Mesozoic and may be present in the fossil record as far back as the Late Triassic, which would make them almost as old as the dinosaurs.
Conversely, any medium that suggests that non-avian dinosaurs coexisted with giant extinct mammals, such as mammoths, sabertoothed cats, or neanderthals. The largest mammals alive during the Mesozoic, or age of the dinosaurs, were about the size of opossums. They didn't start getting big until the dinos weren't around to clog their niches.
That said, the idea that all mammals during the time of dinosaurs were insignificant shrew-like animals that only lived in their shadow is now considered not completely true, as recent finds suggest that they evolved a wide variety of forms during the Mesozoic, including aquatic species, gliding species, burrowing species, grazing species, arboreal species, and even species that ate dinosaurs. Very small dinosaurs.
There is a misleading belief that the mammalian form is somehow "superior" to the archosaurian, and that mammals are inherently more successful and adaptable. In fact, dinosaurs, in the form of birds, currently outnumber mammal species by nearly two to one, and many species, such as crows and parrots, are of comparable intelligence to primates. Indeed, mammals only became dominant over dinosaurs after literal cosmic intervention in the form of a meteor wiped out most of them, and had it not occurred, it's likely non-avian dinosaurs would still rule the Earth today.
There is a tendency (largely carried over from earlier times) to refer to extinct mammals as "X [insert modern mammal's name here]." For instance, referring to a Smilodon as a "sabre-toothed tiger", Thylacoleo as the "marsupial lion", or the thylacine as the "Tasmanian wolf" or "Tasmanian tiger". The marsupial predators of Australia were not at all closely related to wolves, lions, tigers or indeed any other placental predators.
Thanks to Walking with Beasts, it is believed that mammals were still small at the beginning of the Cenozoic era and were prey for killer birds and land crocodiles. In reality, mammalian megafauna first appeared right after the K-Pg extinction event, including carnivores like the creodonts and the hoofed mesonychids.

Sabre-toothed cats

Referring to sabre-toothed cats as "saber-toothed tigers". Machairodontines, or true sabretooths, were an entire subfamily of cats that were no more closely related to the pantherines (tigers, lions, leopards and jaguars) than they were to the felines (pumas, cheetahs, lynxes and domestic cats).
Any time saber-toothed cats are depicted as having proportions like modern cats and long Panthera-like tails. Primitive saber-toothed cats have proportions similar to non-sabertoothed cats, including shorter canines and long tails. As they become specialized, their fangs grow longer, but so do their necks and front legs, while their hind legs become shorter, giving them a loosely hyena-like profile, and their tail becomes stubby like in a bobcat. Smilodon, the most famous sabertooth cat, is also the last in the series and the one where these features are the most exaggerated.
Any time sabretooth cats are fast and agile. They were actually among the slowest predators in Real Life, relying on ambush and strength, not speed or agility, similar to a modern bear. Sabretooth cats could never chase prey. The one big exception to this is Homotherium, the scimitar cat, but it rarely shows up in media anyways.
Sabertooths are sometimes shown using their fangs exclusively and slashing at their prey arbitrarily. Biomechanical studies have shown that their unusual build compared to modern cats is suitable to knock down and hold the prey on the ground before "stabbing" it with the fangs in a meaty, well irrigated area. If Smilodon and co. attacked without securing the prey with their paws first, as they are often seen in fiction, their fragile sabers could break in half.
Smilodon, a strictly American genus, is sometimes placed in any other continent, and often long after every other sabertooth had gone extinct there. It's also often shown living in a snowy environment alongside woolly mammoths, despite ranging farther south in warmer climates. The South American species S. populator was known to have lived in a savannah-like environment which spread much of the Amazon was during the Ice Age, and it didn't live alongside mammoths but rather the elephant-like gomphotheres. On the other hand, the North American species S. fatalis would have seen snow during winter, given California's colder climate at the time, but its range is still far away from woolly mammoths. That species, however, did live alongside the massive Columbian mammoths as well as American mastodons.

Megatherium

Whenever a Megatherium, or giant ground sloth, appears, expect it to be in a perpetual upright stance. In real life, while they would rear up from time to time in order to browse, their limb structure suggests ground sloths walked on all fours. Ground sloths also walked with their hindfeet facing sideways, rather than flat on their soles like in most depictions.
Megatherium is often portrayed with a horse-like head or a dog-like nose, and the oldest portraits even gave it a tapir-like trunk. However, skull studies suggests Megatherium had a narrow muzzle with prehensile lips like a black rhinoceros, and ground sloths would have just two nostrils like modern sloths.
Some depictions of Megatherium show it scavenging on carrion to supplement its diet, or even outright preying on other animals. Modern herbivores do feed on animal matter occasionally, but infrequently and only to obtain specific nutrients not found in their normal diet (eating bones for calcium, for example). Megatherium would have been no exception, and no evidence has been found indicating that it included any substantial amount of meat in its diet.
Old portraits often show Megatherium as being no larger than a bear and brought down by a lone Smilodon. This is significantly inaccurate; Megatherium is as big as modern elephants and the second largest land mammal that isn't an elephant or a rhino, after fellow giant ground sloth Eremotherium, much too big for a sabertooth cat to take down. This may have been due to confusion with other ground sloths such as Megalonyx and Paramylodon, both bear-sized and prey for Smilodon (though not easy prey as commonly depicted, as the sloths can kill the cat with a Deadly Hug similar to how giant anteaters kill their predators).
The popular portrayal of Megatherium as a shaggy beast actually doesn't hold much water. Given the sloth's size and habitat, it was most likely largely hairless.

Mammoths and Mastodons

Mammoths were not the ancestors of modern elephants. Asian elephants are more related to mammoths than to African elephants, but mammoths were direct ancestors of neither.
Mammoths were not all woolly. There were several species of mammoths, the woolly one (Mammuthus primigenius) being only one of them, and it is possible that others were as naked as elephants because they lived in warmer climates. Mammoths appeared in the Pliocene, roughly at the same time as hominids, and the woolly mammoth was the last of them, evolving its thick pelt as protection against the cold, from ancestors that were "naked" instead of the other way around.
Mammoths were not all prehistoric. The last ones died out in Wrangel Island, Siberia, around 1700 BC, when the Egyptians were already building pyramids, though no one knew of them at the time.
Mastodons are often shown looking the same as mammoths, despite being shorter and stockier and having a low-domed skull. Also, there is no evidence that mastodons were furry as commonly portrayed. Given they lived in warmer climates, it's most likely they were as naked as modern elephants or Columbian mammoths, though what little concrete evidence of hair we do have does not rule out patches of it around the shoulders, not unlike a modern bison.
Mammoths and mastodons are regular victims of Bigger Is Better, to the point that "mastodontic" is a synonym of "gigantic" in some languages. There were some truly gigantic mammoths and mastodons: the Steppe Mammoth, Mammuthus trogontherii, was the fourth largest land mammal ever, and one of a handful that routinely surpassed the four meters on shoulder height. It was only itself surpassed by the Indian straight-tusked elephant Palaeoloxodon namadicus and the giant Tertiary rhino-giraffes Paraceratherium and Dzhungariotherium. However, the species usually depicted in media, the woolly mammoth and the American mastodon, were actually smaller than living elephants. In fact, one theory about the American mastodon's extinction is that it was displaced by a newly arrived immigrant to the Americas - the moose.

Other Proboscideans

Referring to elephants or any elephantine creature as a "pachyderm". Despite being cute, the name is now completely outdated and should be forgotten (it arguably would have been if Dumbo hadn't remained so popular). It originally referred to a taxonomic group that included elephants, rhinos and hippos. But now, thanks to anatomical and genetic evidence, we know that, other than being placental mammals, these animals have literally nothing to do with one another. In fact, rhinos are more closely related to horses and tapirs than they are to elephants, and hippos are more closely related to whales.^note
If the gomphothere Platybelodon ever makes an appearance, it will usually be portrayed with a big, flap-like trunk◊ to match with its famous shovel-like lower jaw. In real life, Platybelodon and its similar-looking relatives most likely had long, flexible trunks like modern elephants. The flappy trunk might have been due to the outdated belief Playbelodon was a swamp-dweller using its lower tusks to scoop up food, before its teeth were found to have wear patterns suggesting it ate tough plant material as opposed to soft water plants ^note. Thus, if Platybelodon was a terrestrial browser, it would have required an elephant-like trunk to grasp branches while it used its tusks to cut up the tree.
The term "elephant" being used for any extinct proboscidean, such as mastodons and gomphotheres, despite being in different families. Conversely, there's also mammoths being treated as separate from elephants despite the fact that, being in the Elephantidae family, they technically are elephants.
Deinotherium has been sometimes portrayed with a short trunk, due to deinothere skulls lacking attachment marks for trunk muscles. But since it's been discovered elephants don't have these marks either, it's seems more likely that Deinotherium and its kin had longer trunks. Especially given while their necks are longer than those of elephants, their legs are also longer meaning they would have difficulty kneeling (and therefore unable to drink). It should also be noted Deinotherium has a large nasal bone suggesting it had a powerful trunk, and a longer trunk would endure more strain than a shorter one. That said, some paleontologists stick with the short trunk due to the fact deinotheres are far from elephants, and the drinking problem can be resolved by submerging in water much like how moose drink.

Humans

No, humans did not "evolve from apes". Humans and modern apes share a recent common ancestor from which they diverged. But even that statement is actually inaccurate; humans have not diverged from apes- humans still are apes. Modern genetic classification defines the family Hominidae as including not only humans but all "great apes" (chimps, orangutans, bonobos and gorillas). Works from before the 80s or so restrict Hominidae to humans and use the now-discredited Pongidae for the other great apes.
- There is a lot of confusion about what "evolve from apes" means. Neither "ape" nor "monkey" is a taxonomic term, but everyone has a general idea of what an "ape" or "monkey" looks like. Distant human ancestors include animals that an average observer would describe as an ape or a monkey. Humans don't descend from any modern, currently existing ape or monkey, however. We don't descend from chimpanzees, or gorillas, or macaques.
Despite what certain pictures may tell you, humans did not evolve from chimpanzees, either. Recent finds like Ardipithecus have suggested that chimpanzees' quadrupedal posture is in fact a highly derived form, and that the ancestral "missing link" may look more like us than them.
There is no archaeological evidence that early man used clubs; in fact, the earliest spears are thousands of years older than the earliest clubs. And while many early humans definitely sheltered in caves, there is no way that they all did. Caves are rare, and unlikely to be found on ice age steppeland. Most early men sheltered in huts, much like modern day hunter gatherers. The reason so many of our ancestors' remains are found in caves is because caves are better at preserving human remains than open fields.
Neanderthals are not the ancestors of modern humans. While the genetic relationship between humans and neanderthals is somewhat complicated (nearly everyone not from Africa has a little neanderthal DNA in their makeup), neanderthals were a specifically Eurasian species that evolved to live in the harsh northern Ice Age climate. Modern humans may have interbred with neanderthals when they reached their territory, but they did not evolve from them, since they first appeared in Africa, and therefore no native Africans have any neanderthal DNA.
Neanderthals are often depicted in media as being dumb, brutish, and uncivilized, sometimes bordering on Frazetta Man. Recent evidence has suggested that they were in fact as intelligent and cultured as the other species of human at the time, known for skilled cooperative hunting, possible medical practices, and even maritime travel.

Other Mammals

Cave bears will usually be portrayed as carnivores in the media, when their dentition and isotope analysis suggest they were herbivores. That said, they probably would have eaten meat if the opportunity arose, much like the giant panda.
Any time Gigantopithecus is portrayed walking upright like a human, mainly in order for it to associate with Bigfoot. While Gigantopithecus is only known from teeth and jawbones, its close relationship with modern apes, particularly the orangutan, strongly suggests it walked on all fours (it was once thought to be very closely related to humans, but this seems to be incorrect; orangutans and humans have very similar teeth anyway).
Andrewsarchus was initially thought to have been a relative of mesonychids due to similarities in teeth and skull, and Walking with Beasts perpetrated this portrayal◊. Recent studies have shown it was actually an artiodactyl closely related to entelodonts as well as hippos and cetaceans; it would have most likely looked more like a pig with the head of a wolf as opposed to simply a wolf with hooves. With that said, its exact appearance is currently impossible to clarify since it is only known from the aforementioned teeth and skull, but it was most likely different than its traditional wolf-like portrayals.
Glyptodonts are often portrayed withdrawing their heads into their shells like turtles, which they couldn't in real life. They were actually more like ankylosaurs, having body armor that covers only the topside of the body leaving their undersides unprotected.
The giant short-faced kangaroo Procoptodon being portrayed hopping as a mode of transportation and having a body plan just like its modern-day relatives. In real life, Procoptodon was unable to hop due to its weight and instead walked bipedally like a human or a theropod would. Its single hoof-like toe means it would have been digitigrade, instead of plantigrade like today's kangaroos, and it also would have a thicker tail.
Dire wolves draw a lot to fantasy imagination, but in real life, while they were the largest wolves to ever live, they weren't nearly as big as fantasy portrays. They were only slightly larger than modern grey wolves. The largest canid was a Epicyon, which was half as tall as an average human. Larger was Pseudocyon, a species of what are called 'bear-dogs.'
Depicting Basilosaurus and other proto-whales with necks and lipless mouths.
The South American litoptern Macrauchenia being portrayed with a tapir-like proboscis. Its skull wasn't really tapir-like at all◊, lacking the large bony projection tapirs use as an anchor for their trunks, and thus it more likely had a bulbous nose like a moose or saiga antelope.
Elasmotherium was traditionally portrayed as "unicorn-like", with a 2-meter-long horn. However, a 2021 paper has challenged this notion, and it was more likely the mammalian equivalent to Pachyrhinosaurus.

Invertebrates

Thanks to them being Big Creepy-Crawlies the giant arthropods of the past (particularly the Carboniferous, the era of big bugs) suffer a lot from the Prehistoric Monster trope. Some of them were predators yes, but some were pretty harmless herbivores. Arthropleura is probably the biggest victim of this; despite the fact it was a herbivore a lot of works involving it show it as a scary predatory animal.
Speaking of Arthropleura, thanks to Rule of Scary they are sometimes shown as being centipede like in shape even though they were a type of gigantic millipede.
Portraying eurypterids (sea scorpions) only as scorpions that know how to swim. For one thing the creatures came in more shapes and sizes than just scorpion-like.◊, For another they had several differences, most notably their tails didn't have stingers. And while they’re closely related to scorpions and other arachnids, they are not part of the arachnid group. In fact one of the closest known ancestors to scorpions, Brontoscorpio, an actual aquatic scorpion, isn’t actually part of the eurypterid (sea scorpion) order, which are actually more closely related to horseshoe crabs (which aren't a type of crab either). Classification can be weird sometimes.
Portraying Megarachne as a Giant Spider any time after 2005. This was one of the big issues with Walking with Monsters—the show was in mid-production right when it was discovered that Megarachne wasn't actually a spider. They couldn't remove it from the show, so they kept it in and just called it a "Mesothelae", a hypothetical member of a primitive spider group.
Often, ammonites will be depicted with dull, brownish-grey shells, as if they were wearing their actual rock fossils. Of course, nautiloids and marine gastropods also have dull, brownish-grey fossil shells, but we know from living species that their shells are often very colourful and vibrantly patterned. Most ammonites probably also had very colourful and vibrantly patterned shells, but they just don't preserve in the fossils.
Portraying Meganeura and other similarly large arthropods as living alongside the dinosaurs. The giant dragonfly-like insect Meganeura only lived in the Late Carboniferous, and its relatives only ranged to Late Permian. As mentioned in the "Age of the Dinosaurs" folder, such arthropods only got so big due to factors like the higher oxygen concentration of the Carboniferous and the unoccupied niches on land, meaning they didn't coexist with dinosaurs in the Mesozoic.

Analysis / Artistic License – Paleontology

Common Inaccuracies In Media

Paleontology

Dinosaurs

Saurischians

Ornithischians

Pterosaurs

Marine Reptiles

Pseudosuchians

Fish

Synapsids

Invertebrates

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Analysis / Artistic License – Paleontology

Edit Locked

Common Inaccuracies In Media

Paleontology

Dinosaurs

Saurischians

Ornithischians

Pterosaurs

Marine Reptiles

Pseudosuchians

Fish

Synapsids

Invertebrates

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