At a first glance, sauropod predecessors (traditionally called prosauropods, before the sauropods) seem looking all alike, with the same mixed theropod/sauropod shape that characterize the most famous kind, Plateosaurus. Actually their resemblance was not necessarily a real sign of relationship: their bodyplan 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 ensembles: core prosauropods, near sauropods and really basal sauropodomorphs. The first were typical "prosauropods", large to medium-sized bipedal dinosaurs including Plateosaurus among them. The second ones were more closely related to sauropods and gave rise to them, and were usually larger than the former (and some were capable of some quadrupedality). The third ones were 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 isnt any external trait which allows to distinguish these groups. Even their period is not indicative: both Late Triassic and Early Jurassic were inhabited by core prosauropods and near sauropods, to say. However, we put here all the examples of "prosauropods" together, specifying for each its possible placement in the evolutionary tree.
An Old Story: Thecodontosaurus
- Thecodont ("teeth in sockets") is the traditional catch-all name for the basal non-dinosaurian Triassic archosaurs and archosauromorphs like Euparkeria, phytosaurs, rauisuchians, aetosaurs, and so on. Thus, it could seem that the deceptively-named Thecodontosaurus was one of them: actually was a true dinosaur, albeit one of the most primitive known. Triassic and European just like Plateosaurus, Thecodontosaurus was also one of the first-discovered dinosaurs, in England, and initially was not classified as a dinosaur. Only 2 m long, Thecodontosaurus antiquus (antiquus = ancient) was the most theropod-like among the classic "prosauropods"; in modern taxonomy, is considered a really basal sauropodomorph. Long considered the most archaic "prosauropod", the thecodontosaur has recently lost its record in favor of other dinosaurs — among them, maybe even some putative theropods like Eoraptor and Guaibasaurus. Some Thecodontosauruses have recently been re-classified in another genuses (Asylosaurus, Pantydraco).
Mickey Mouseosaur: Mussaurus
- Discovered in 1979 in Triassic Argentina, the unusually short-named Mussaurus (mouse reptile) was a near sauropod whose only remains are from newborns the size of a house mouse (hence the name), which died just after being hatched. Astonishingly some thought that these remains were from adults, and many popular books have then reported Mussaurus as a literally mouse-sized dinosaur: some went even further by claiming it was the smallest dinosaur ever (or at least the smallest herbivorous one). Popular portrayals of the mussaur, maybe first-inspired by John Sibbick, often depicted the adult form as quadruped animals with the same large head and short neck of the hatchlings. It should be remembered that dinosaurs were not like the distantly-related snakes and lizards, whose youngster are miniaturized images of the adults; the dinosaurs nestlings were more like those of the closerly-related birds and crocodilians, both with childlike, cuteness-inspiring traits which get lost in adults. Since adult skeletons of Mussaurus have never been discovered so far, obviously we dont know how big the adult was: but almost certainly it was at least as large as a human and had the classic small head and long neck of all "prosauropods". We don't know if it was bipedal or quadrupedal. Some suspected the 4 m long Coloradisaurus (from Argentina like Mussaurus, not from Colorado!) was in fact the adult form of Mussaurus, but the former is known only from a skull, and was closer to Plateosaurus than to the "mouse-dinosaur".
- Riojasaurus has been, in a sense, the polar opposite of Mussaurus in popular dino-books. Its Spanish-sounding name reveals it also lived in Late Triassic Argentina like the "mouse-reptile" (La Rioja is a northern province of Argentina), but was bigger. More than 10 m long and perhaps heavier than an average elephant, was one of the largest land animals of the Triassic, even bigger than Plateosaurus itself, only equalled in weight by other "prosauropods" like Yunnanosaurus and the recently discovered mammal-ancestor Lisowicia. Like other prosauropods, the riojasaur has left abundant record (more than 30 individuals). Indeed, at a first glance, Riojasaurus resembles more a sauropod, with the same size of many small true sauropods like Saltasaurus, Amargasaurus and Shunosaurus, massive limbs and stocky body. However, the structure of its feet with distinct digits and its plateosaur-like skull are typically "prosauropodian". Recent research indicates that Riojasaurus was a core prosauropod like Plateosaurus, and not a sauropod-ancestor as previously proposed. Melanorosaurus (the "lizard from the Black Mountain") could be considered the Riojasaurus South African "twin". Contemporary to it, from Late Triassic, the two dinosaurs maybe could have met in life, since Africa and South America were reuned in the Pangea at the time. Both the same size, with the same robust sauropodian shape but "prosauropod"-like feet, they were perhaps mainly quadrupedal. Both were candidates for the title of the ancestor of all sauropods: recent research has shown Melanorosaurus was indeed a "near sauropod", and the riojasaurs similar frame was obtained by convergent evolution.
Dinosaurs in Stamps: Lufengosaurus
- Lufengosaurus ("Lu-feng lizard") has been the most well-known early dinosaur from China, with about 40 skeleton 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. 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: it owes its name to the southern chinese province of Yunnan. Traditionally extimated 7 m long, one recently-found Yunnanosaurus species is 13 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.
Good-legged Dinosaur: Euskelosaurus
- Other "near sauropods" similar to Melanorosaurus were Blikanasaurus ("lizard from Mount Blikana", also South African), the Chinese Chinshakiangosaurus (Chinshakiang is the upper portion of the Yangtze-Kiang river)note , and the English Camelotia or "Avalonia". But 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. 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"). While one fragmentary remain of the latter was once believed from a giant Triassic theropod related with herrerasaurians, "Aliwalia rex". Unaysaurus was found in Brazil in the 2000s: it has left good remains, and was probably closely related with Plateosaurus.
From Europe to the South Pole: "Sellosaurus" & Glacialisaurus
- A slighty 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 and Moroccan Azendohsaurus) have revealed pertaining to non-dinosaur dinosauromorphs. While the allegedly Australian Agrosaurus (long believed the most ancient dinosaur of that continent) has revealed being a Thecodontosaurus specimen originally found in England. One prosauropod was found even in Antarctica, during the late 2000s: Glacialisaurus ("lizard from ice"), the third described dinosaur in the continent after Cryolophosaurus and Antarctopelta. It shows in Dinosaur Revolution as the opponent of the cryolophosaur.