In 1993, the first news of a nearly complete, one-meter-long skeleton of an early bipedal dinosaur was published (Sereno et al. 1993). This was Eoraptor lunensis, a medium-sized carnivore found in the Ischigualasto Formation of northwestern Argentina. The find occurs alongside other early dinosaurs and their kin, such as Herrerasaurus and Pisanosaurus.
Scan of Eoraptor skull using high-resolution X-ray computed tomography.
Eoraptor lacks the specialized features of any of the major groups of dinosaurs, and is quite similar to what would be expected for dinosaur ancestors. This has led some to conclude that it is not part of the dinosaurs proper, but is a closely related archosaur. Others have pointed to the functionally three-fingered hand as an indication of close ties to theropod dinosaurs.
In any case, the traits of Eoraptor suggest that the first dinosaurs were small, bipedal predators. Taken together, the finds at Ischigualasto demonstrate that dinosaurs had radiated by the Late Triassic.
Original page created by Brian Speer 11/1997; modifications since 2005 by David Smith. Eoraptor image © DigiMorph.org.