Plateosaurus (Wikimedia Commons).


Plateosaurus (Greek for "flat lizard"); pronounced PLATT-ee-oh-SORE-us


Plains of Western Europe

Historical Period:

Late Triassic (220-210 million years ago)

Size and Weight:

Up to 25 feet long and four tons



Distinguishing Characteristics:

Partially opposable thumbs; small head on long neck; occasional bipedal posture


About Plateosaurus

Plateosaurus was the prototypical prosauropod--the family of small-to-medium sized, occasionally bipedal, plant-eating dinosaurs of the late Triassic and early Jurassic periods that were distantly ancestral to the giant sauropods and titanosaurs of the later Mesozoic Era.

Because so many of its fossils have been unearthed across the expanse of Germany and Switzerland, paleontologists believe Plateosaurus roamed the plains of western Europe in sizable herds, literally eating their way across the landscape (and staying well out of the way of comparably sized meat-eating dinosaurs like Megalosaurus).

The most productive Plateosaurus fossil site is a quarry near the village of Trossingen, in the Black Forest, which has yielded the partial remains of over 100 individuals. The most likely explanation is that a Plateosaurus herd became mired in deep mud, after a flash flood or a severe thunderstorm, and perished one on top of each other (in much the same way the La Brea Tar Pits in Los Angeles have yielded numerous remains of the Saber-Toothed Tiger and the Dire Wolf, which likely got stuck while trying to pluck out already-mired prey). However, it's also possible that some of these individuals accumulated slowly at the fossil site after drowning elsewhere and being carried to their final resting place by the prevailing currents.

One feature of Plateosaurus that has caused raised eyebrows among paleontologists is the partially opposable thumbs on this dinosaur's front hands. We shouldn't take this as an indication that the (fairly dumb by modern standards) Plateosaurus was well on its way to evolving fully opposable thumbs, which are believed to have been one of the necessary precursors of human intelligence during the late Pleistocene epoch.

Rather, it's likely that Plateosaurus and other prosauropods evolved this feature in order to better grasp the leaves or small branches of trees, and--absent any other environmental pressures--it wouldn't have developed any further over time. This presumed behavior also explains Plateosaurus' habit of occasionally standing on its two hind legs, which would have enabled it to reach higher and tastier vegetation.

Like most dinosaurs discovered and named in the mid-19th century, Plateosaurus has generated a fair amount of confusion. Because this was the first prosauropod ever to be identified, paleontologists had a hard time figuring out how to classify Plateosaurus: one notable authority, Hermann von Meyer, invented a new family called "pachypodes" ("heavy feet"), to which he assigned not only the plant-eating Plateosaurus but the carnivorous Megalosaurus as well! It wasn't until the discovery of additional prosauropod genera, like Sellosaurus and Unaysaurus, that matters were more or less sorted out, and Plateosaurus was recognized as an early saurischian dinosaur. (It's not even clear what Plateosaurus, Greek for "flat lizard," is supposed to mean; it may refer to the flattened bones of the original type specimen.)