Sanjuansaurus (Greek for "San Juan lizard"); pronounced san-wahn-SORE-us
Woodlands of South America
Middle Triassic (230 million years ago)
Size and Weight:
About 5 feet long and 50 pounds
Small size; bipedal posture
Barring a better hypothesis, paleontologists believe that the first dinosaurs, the early theropods, evolved in South America about 230 million years ago. Discovered recently in Argentina, Sanjuansaurus seems to have been closely related to the better-known basal theropods Herrerasaurus and Eoraptor. (By the way, some experts maintain that these early carnivores weren't true theropods at all, but rather predated the split between saurischian and ornithischian dinosaurs).