Size and Weight:
Known from a single fossil specimen discovered in South America in 1970, Staurikosaurus was one of the first dinosaurs, the immediate descendants of the two-legged archosaurs of the early Triassic period. Like its slightly bigger South American cousins, Herrerasaurus and Eoraptor, it seems that Staurikosaurus was a true theropod--that is, it evolved after the ancient split between ornithischian and saurischian dinosaurs.
One odd feature of Staurikosaurus is a joint in its lower jaw that apparently allowed it to chew its food backwards and forwards, as well as up and down. Since later theropods (including raptors and tyrannosaurs) didn't possess this adaptation, it's likely that Staurikosaurus, like other early meat-eaters, lived in a stark environment that forced it to extract the maximum nutritional value from its wriggling meals.