PSITTACOSAURUS

genus of small dinosaurs found as fossils in Early Cretaceous deposits (144 to 97.5 million years ago) of Mongolia and China. Psittacosaurus, which was ancestral to or related to the horned dinosaurs, was primitive and at least occasionally bipedal. The hind limbs and pelvis were well developed and characteristic of the ornithischian dinosaurs (those with a birdlike pelvis). Although the forelimbs were not as large or massive as the hind limbs, it is probable that Psittacosaurus was able to assume a quadrupedal pose, perhaps for feeding. It was about 2 m (6 feet) long. The skull was high and narrow. The anterior region was very much like a parrot's beak, and the upper jaw curved over the lower. Teeth, absent from the anterior portions of the jaw, were present in the cheek region.