The complete skull and skeleton of an early dinosaur.

The unearthing of a complete skull and skeleton of the early dinosaur Herrerasaurus ischigualastensis sheds light on the early evolution of dinosaurs. Discovered in the Upper Triassic Ischigualasto Formation of Argentina, the fossils show that Herrerasaurus, a primitive theropod, was an agile, bipedal predator with a short forelimb specialized for grasping and raking. The fossils clarify anatomical features of the common ancestor of all dinosaurs. Herrerasaurus and younger dinosaurs from Upper Triassic beds in Argentina suggest that the dinosaurian radiation was well under way before dinosaurs dominated terrestrial vertebrate communities in taxonomic diversity and abundance.