At a first glance, sauropod predecessors (traditionally called prosauropods, "before the sauropods") look all alike, with the same mixed theropod/sauropod shape that characterizes the most famous genus, Plateosaurus (the animal in the image). However, their resemblance is not necessarily a real sign of relationship: their body plan was simply a primitive condition shared by the most basal Sauropodomorpha (lit. "shaped like a sauropod").
According to recent classifications, the prosauropods in traditional sense can be divided in three groups: "core prosauropods", "near sauropods" and "really basal sauropodomorphs". The first are typical "prosauropods", large to medium-sized bipedal or semibipedal dinosaurs including Plateosaurus among them. The second ones are more closely related to sauropods and gave rise to them, and were usually larger than the former (and some were obligate quadrupeds). The third ones are more primitive than both "core prosauropods" and "near sauropods", and include the common ancestor of all the other sauropodomorphs.
As none of these are natural groupings, there isn't any external trait which allows them to be distinguished. Even their period is not indicative: both the Late Triassic and Early Jurassic were inhabited by "core prosauropods" and "near sauropods". However, we put all the examples of "prosauropods" together here, specifying for each its possible placement in the evolutionary tree. Plateosaurus, Riojasaurus and Massospondylus are "core prosauropods", while Mussaurus and Anchisaurus are considered "near sauropods". Thecodontosaurus is regarded as the classic example of a "really basal sauropodomorph", but also Eoraptor, classically believed a proto-theropod or a basal dinosaur, was among them according to the last researches.
Giant Quadrupedal Prosauropod: Melanorosaurus
- Some sauropod-predecessors were as big and as massive as several "small" sauropods like Saltasaurus or Shunosaurus. Melanorosaurus (the "lizard from the Black Mountain") has been one of the most famous together with the South-American Riojasaurus, and because of its shape and size it could be considered its South African "twin". Contemporary to it, from Late Triassic, the two dinosaurs maybe could have met in life, since Africa and South America were part of a single supercontinent, Pangea, at the time. Both the same size, with the same robust sauropodian shape but "prosauropod"-like feet, they were mainly quadrupedal unlike the classic image of two-legged prosauropods. Both were candidates for the title of "the ancestor of all sauropods": recent research has shown that while the riojasaur was a "core prosauropod" distantly-related with true sauropods, Melanorosaurus was indeed a "near sauropod", and the riojasaur's similar frame was obtained by convergent evolution. Other "near sauropods" similar to Melanorosaurus were Blikanasaurus ("lizard from Mount Blikana", also South African) and the Chinese Chinshakiangosaurus (Chinshakiang is the upper portion of the Yangtze-Kiang river). Both are often classified today as very basal true sauropods like Barapasaurus and Vulcanodon. The English Camelotia or "Avalonia" was also a "near-sauropod".
Dinosaurs in Stamps: Lufengosaurus
- Lufengosaurus ("Lu-feng lizard") has been the most well-known early dinosaur from China, with about 40 skeletons discovered. It was a "core prosauropod" closely related to Massospondylus but bigger. It actually looked more like Plateosaurus — to the point it could even be considered its eastern twin, only smaller (6 m long). One of the last-surviving prosauropods, Lufengosaurus was originally believed to have lived in Late Triassic: then it was more correctly put in the Early Jurassic, but the most recent findings showed it reached even the Middle Jurassic: enough to encounter the first true sauropods such as the club-tailed Shunosaurus. Unaysaurus was found in Brazil in the 2000s: it has left good remains like the lufengosaur, and was probably closely related with Plateosaurus. Lufengosaurus was also one of the first dinosaurs found in China (1940s), and the first dino around the world to have been portrayed in a postage-stamp. "Mailing With Dinosaurs" began much earlier than the production of "Walking With Dinosaurs" in 1999.
Sauropod Teeth: Yunnanosaurus
- Yunnanosaurus lived in the same epoch/places of Lufengosaurus and was related to it: it owes its name to the southern Chinese province of Yunnan. Traditionally estimated the size of a Plateosaurus, one recently-found Yunnanosaurus species is 10 m long, and now is one of the biggest "prosauropod" known, rivalling the "core prosauropod" Riojasaurus of Triassic South-America and the "near-sauropod" Melanorosaurus of Triassic South-Africa. But Yunnanosaurus is also worthy of note because of its strange unique chisel-like teeth, more similar to those of sauropods than to a typical prosauropod — a classic case of convergent evolution, as the yunnanosaur was not one of the direct ancestors of sauropods as once thought because of its teeth.
Similar to Plateosaurus: Euskelosaurus
- There were also some "core prosauropods" living alongside Melanorosaurus in South Africa: among them, Euskelosaurus ("lizard with good legs") was only slightly smaller than Melanorosaurus, but was related with Plateosaurus. Once a well-known prosauropod genus, today many of its remains are now believed pertaining to other relatives, ex. the similarly-named Eucnemesaurus ("lizard with good knees"). This one was probably closer to the gigantic Riojasaurus than to Plateosaurus or Euskelosaurus. One fragmentary remain of Eucnemesaurus was once believed from a giant Triassic theropod related with herrerasaurians, "Aliwalia rex".
Double Identity: "Sellosaurus" & Efraasia
- A slightly more derived “really basal sauropodomorph” from Europe than Thecodontosaurus is Efraasia, which was once thought to be the young of another European dinosaur, Sellosaurus. The latter used to be known from numerous remains found near those of Plateosaurus... indeed, even though "Sellosaurus" was once thought a large relative of Anchisaurus, today is now often thought to be a simple species of Plateosaurus. Science Marches On frequently with the sauropod predecessors: for example, some fragmentary fossils once classified as "prosauropods" (ex. Canadian Arctosaurus, "arctic lizard", and Moroccan Azendohsaurus) have revealed pertaining to non-dinosaur dinosauromorphs. While the allegedly Australian Agrosaurus ("field lizard", long believed the most ancient dinosaur of that continent) has revealed being a Thecodontosaurus specimen or a thecodontosaur relative originally found in England.
All-Eating?: Guaibasaurus & Saturnalia
- Some basal saurischians have traditionally made together the Guaibasaurids: these saurischians were extremely generic and unspecialized dinosaurs, known only since the 2000s. Their external shape was in the middle between a small theropod and a basal sauropodomorph, not deceptively theropodian like Eoraptor. The namesake Guaibasaurus from the extreme south of Brazil (Rio Grande Do Sul) was the first discovered; then, the mythical-named Saturnalia, also from the Deep South of Brazil. "Saturnalia" is a plural Latin name for a kind of feast made by Ancient Romans to celebrate Saturn, the god who protected their crops — incidentally, another astronomical-named ancestral dinosaur (the planet Saturn) like the herrerasaur Staurikosaurus: also found in the Brazilian state of Rio Grande do Sul (near Argentina), the staurikosaur was potentially one of its predators, being a bit bigger. Saturnalia was initially believed the "first prosauropod". In the second half of the 2000s scientists decided that both dinosaurs were too basal to be either theropods or sauropodomorphs, and put together in the same family, Guaibasaurids. Now they are often considered very basal sauropod-predecessors, though this, too, may still change. Recently they have been put in two distinct families, the proper Guaibasaurids and the Saturnalids. With their unspecialized traits, these dinosaurs were almost surely omnivorous creatures; indeed, a saturnalid found in 2009 in Argentina has received a meaningful name: Panphagia, "eat-all".
From the South Pole to the North Pole: Glacialisaurus & Issi
- Prosauropods have been found everywhere, even in the most remote places. One of them, for example, was found in Antarctica during the late 2000s: Glacialisaurus ("lizard from ice"), the third described dinosaur in the continent after Cryolophosaurus and Antarctopelta. Middle-sized and related with Massospondylus and Lufengosaurus, it shows in Dinosaur Revolution as the opponent of the cryolophosaur. In 2021, the first sauropod-ancestor was described in Greenland, near the North Pole: Issi saaneq ("Cold Bones" in Greenlandic), the only non-bird dinosaur genus known from the great icy island near Canada. Discovered in The New '10s, it was originally considered a specimen of Plateosaurus, and is still considered one of the closest plateosaur-relatives among sauropod-predecessors. Both Glacialisaurus and Issi were dug out from the few ice-free portions of the two polar lands, like Antarctopelta and Cryolophosaurus.
