Size and Weight:
Known from a single fossil specimen found in South America in 1970, Staurikosaurus is one of the earliest dinosaurs, the immediate descendants of the two-legged archosaurs of the early Triassic period. Unlike its slightly bigger South American cousin, Herrerasaurus, it seems that Staurikosaurus was a true theropod--that is, it evolved after the ancient split between ornithischian and saurischian dinosaurs.
One odd feature about Staurikosaurus was a joint in its lower jaw that seemed to allow it to chew its food backwards and forwards, as well as up and down. Since later theropods didn't have this adaptation, it's likely that Staurikosaurus lived in an stark environment that forced it to extract the maximum nutrition from its wriggling meals.