Protoceratops andrewsi Archosauria: Ornithischia: Ceratopsia: Protoceratopsidae Locality: Tugrikin Us, Gobi Desert, southern Mongolia Age: Late Cretaceous (Campanian), 75 million years ago   Protoceratops andrewsi is one of the best known dinosaurs ever. Literally hundreds of individuals have been collected in central Asia, and sometimes this species makes up more than 80% of all the dinosaurs known from a site. All stages of growth are known from unhatched eggs containing embryos to hatchlings to 'teenagers' to male and female adults. Because so many stages of life of this sheep-sized dinosaur are known, paleontologists have been able to understand how the skeleton changed throughout the life of the individual-something quite rare to know about fossil animals. It is typical for the young of many living land vertebrates to have a larger head relative to the remainder of the body than is seen in adults. Comparison between the two skeletons of Protoceratops andrewsi, the hatchling and the adult, shows that this species followed the same pattern. Protoceratops seems to have lived in large groups, perhaps forming nesting colonies along the shores of ancient lakes and streams that lay in an otherwise arid landscape. The catastrophies that can occur in such an environment, such as flash floods or extended drought coupled with the natural instinct of these dinosaurs to congregate, probably led to the unusual abundance of this group in the fossil record. Although Protoceratops andrewsi is a neoceratopsian (a group of dinosaurs which typically have horns) there were none on this species, just low bony knobs of bone on the skull. The descendants of Protoceratops andrewsi probably emigrated from Asia to North America where they eventually gave rise to such well known dinosaurs as Triceratops, which does have horns. The expansion of bone at the back of the skull, or the 'frill' as it is commonly known, functioned to redirect the muscles that controlled the lower jaw so they acted more efficiently. The frill may also have played a role similar to horns in antelope where they act to establish social dominance between individuals of a group and to help animals within a species recognize another of their species especially during breeding times. The eggs and skeleton of Protoceratops andrewsi illustrate the various stages of life that these animals went through. As with many vertebrates as they grow, the proportions of the skeleton of the juvenile are different from those of the adult. Both the protoceratopsids and ceratopsids were bulky quadrupedals. The protoceratopsids were small- or medium-sized forms, whereas the largest ceratopsids reached up to 8 meters in length and looked somewhat similar to modern rhinoceros. The protoceratopsids are known from Central Asia and West of North America. This group gave rise to ceratopsids that were more evolutionarily advanced and known only from the West of North America. One of the main difference between protoceratopsids and ceratopsids is their skull structure. In both these groups the rear part of the skull roof forms a large bony 'frill', while the ceratopsians also possessed variously developed horns on the nasal bones and above the orbits as well as along the edge of the frill. |
