Herrerasaurus

Herresaurus was one of the earliest dinosaurs. This dinosaur lived during the Middle Triassic Period in Argentina. The names Ischisaurus and Frenguellisaurus are synonymous with Herrerasaurus. The name of this carnivore means "Herrera's lizard". It was lightly built carnivore that was estimated 4-6 meters long and weighed about 400 kilos.  The skull of this dinosaur was 56 centimeters long. It resembled skulls of more primitive archosaurus such as Euparkeria.

Herrerasaurus was one of the dominant theropods of the Late Triassic of South America.  It probably captured small animals by ambush and surprise. Its prey included rhynchosaurs, thecodont reptiles, and other early dinosaurs. Herrerasaurus lived around 230 million years ago, when dinosaurs first appeared in the Triassic Period but were not yet dominant. These earliest dinosaurs were all small predators, like Coelophysis in North America. They competed with more powerful nondinosaur carnivores for food, including the rauisuchids, some of which were like huge crocodiles. Larger predators ate Herrerasaurus and other small dinosaurs.

Herrerasaurus represents the roots of dinosaur evolution. It cannot be classified as either a Saurischia or Ornithischia. This early and very primitive dinosaur had four toes on its back feet. This separates it from other meat-eating dinosaurs, which had three toes. It was advanced in other ways, however. Its pelvis and vertebrae (back bones) were similar to the advanced theropods of the Jurassic and the Cretaceous Periods. 

The first Herrerasaurus fossil was found in 1958 by Don Victorino Herrera, a local rancher. Three partial skeletons have been found. The first Herrerasaurus skull wasn't found until 1988.