Part of Hall of Ornithischian Dinosaurs.

Psittacosaurus model in the Hall of Ornithischians. D. Finnin/© AMNH

At 4 feet long and 2 feet tall, Psittacosaurus (pronounced sih-TACK-oh-sore-us) lived some 100 million years ago. Despite the fact that it didn't have any horns, Psittacosaurus was a member of the same group as Triceratops.

Psittacosaurus was named for its prominent rostral bone, which formed the tip of its upper beak. The front of its jaw was used to crop vegetation before the food was chewed, swallowed, and ground between stones in its gizzard.