Psittacosaurus mongoliensis

Psittacosaurus is one of the oldest and most primitive ceratopians ever found. Unlike later ceratopians such as Triceratops and Protoceratops, this small dinosaur was bipedal (stood on two legs), and lacked horns. Psittacosaurus was about as tall as an eight-year-old child.

Image credits: main image, courtesy of AMNH/Kelvin Chan.