HERRERASAURUS (huh-RARE-uh-SORE-us)

Period: Late Triassic

Family: Herrerasauridae

Location: South America (Argentina)

Length: 10 feet (3 meters)

This carnivore weighed perhaps 500 pounds and stood about four feet tall at the shoulders. Herrerasaurus was one of the dominant theropods of the Late Triassic of South America. The skull is unknown, but the other parts of the skeleton show that Herrerasaurus was a meat-eater that had muscular jaws, cutting teeth, and claws on the front feet. The pubis of Herrerasaurus is unusual; it looks much like the pelvis of later ornithischian dinosaurs. Herrerasaurus may be close to the ancestry of several major groups of dinosaurs.

Herrerasaurus lived among groves of ferns and tall conifer trees in a cool, moist habitat. 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.

Staurikosaurus, which some paleontologists place in the same family with Herrerasaurus, also had four toes on its back feet. Herrerasaurus was slightly more advanced in the hips, however, showing that it may be an ancestor that led to the prosauropod dinosaurs.

Herrerasaurus is known best from the Ischigualasto Formation in the Valle de la Luna (Valley of the Moon) National Park in San Juan, Argentina. A goat farmer, Victorino Herrera, found the skeleton and the dinosaur was named after him. The barren landscape has hills of red, purple, green, and tan shale. It is similar to the landscape in the Petrified Forest National Park in Arizona, where the Chinle Formation of about the same age has produced similar dinosaurs.