HERRERASAURUS

genus of extremely primitive theropod dinosaurs found as fossils in Late Triassic deposits (dating from 230 to 208 million years ago) of Argentina. Fragmentary fossil remains of them were discovered in the early 1960s, and in 1988 the discovery of several fossil skeletons in the Ischigualasto Formation of northwest Argentina gave researchers the first complete picture of an early dinosaur. Herrerasaurs were the earliest-known carnivores in the dinosaur family. They had a bipedal stance; long, powerful hind legs for running; short forelimbs equipped with three recurved claws for grasping and raking; a flexible lower jaw for holding the prey; and large inward-curving teeth. Herrerasaurs reached a length of about 3 m (10 feet) and weighed about 180 kg (400 pounds). The discovery of herrerasaur remains helped clarify the sequence of anatomical changes that occurred during early dinosaur evolution. They closely resembled the common ancestor of all dinosaurs, but their skull, neck, and forelimb bones show them to be a branch of early saurischians known as theropods. They flourished at a time just before dinosaurs became the dominant animals on land.