PROTOCERATOPS

extinct genus of primitive dinosaurs found as fossils in Gobi (desert) deposits of the Cretaceous Period (144 to 66.4 million years ago). Protoceratops, a predecessor of the more familiar horned dinosaurs, is one of the most primitive members of the last major group of dinosaurs to evolve. It may have evolved from a small biped but moved about on all four limbs; the hind limbs were more strongly developed than the forelimbs, giving the back an arched appearance. Although small for a ceratopsian dinosaur, Protoceratops was still a relatively large animal. Adult individuals were about 2 m (7 feet) long and must have weighed about 180 kg (400 pounds). The skull was very long, about one-fifth the total body length. Bones in the skull had grown backward into a perforated frill that probably served as a surface for the attachment of chewing muscles, for the attachment of muscles that controlled head movements, and for shielding the vulnerable neck region from attack by predators. The jaws were beaklike, and teeth were present in the upper and lower jaws. An area on top of the snout of fossil specimens may mark the position of a hornlike structure. The tail was well developed, with long vertebral spines, suggesting to some theorists that Protoceratops may have been at least partially aquatic in habit. The remains of more than 80 individuals have been found in all stages of growth; the remains include newly hatched young and whole and broken eggs, some with the remains of embryos in them. The eggs, about 15 cm (6 inches) long and ellipsoidal in shape, appear to have been laid in circular clusters. Because of the unusually complete series of remains known, it is possible to work out the rates and manner of growth of Protoceratops and to study the range of variation evident in the genus.