Triassic Period

Triassic Dinosaurs

Why is Herrerasaurus ischigualastensis thought to be one of the earliest dinosaurs known?

Based on the characteristics of its skeleton—a blend of archosaur and dinosaur features—scientists believe the Herrerasaurus ischigualastensis was an early dinosaur. Initially, scientists new this 10-to 18-foot (3-to 6-meter) carnivorous reptile had a skull and foot similar to other archosaurs such as the Euparkeria. Based only on this evidence, it was impossible to determine if the Herrerasaurus was truly a dinosaur. But using the modern cladistic test, the Herrerasaurus skeleton shows all but a few of the characteristics that define dinosaurs. In particular, Herrerasaurus lacks bone in the center of the hip socket, a key characteristic that defines this reptile as a true dinosaur—and one of the earliest known.


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