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Pssittacosaurus mongoliensis

The small asian dinosaur, Psittacosaurus ("parrot reptile") was so named for its distinctive bird-like beak. It was small (by dinosaur standards), only reaching lengths of 2 meters and standing (on its two hind legs) about as tall as a small adult human. During the 1980s, Dr. Walter Coombs was studying the material from the R.C. Andrews expeditions and uncovered two tiny skeletons (40 cm and 25 cm long). The large eyes and bone arrangements led him to conclude that these were hatchling psittacosaurs. The tooth wear in these tiny creatures is evidence that they were independent enough to eat abrasive plant material at an early age.

Discovery
Between 1922 and 1930, Roy Chapman Andrews led five expeditions for the American Museum of Natural History to the wilds of the Gobi Desert in Mongolia. This colorful naturalist and explorer (and perhaps the model for Indiana Jones) was looking for fossils of early man, but instead found extraordinary dinosaurs. In these badlands of Mongolia, his expeditions found the skeletons of the oldest and most primitive ceratopsian dinosaur: Psittacosaurus.
Taxonomy

Marginocephalians are all distinguished by some sort of bony frill or border at the back of the skull. All ceratopsians and pachycephalosaurs have this trait to a greater or lesser degree. The ceratopsian dinosaurs split from the pachycephalosaurs at the next level of distinction. The ceratopsians are a large and diverse group of plant-eaters that include, not only Protoceratops and Triceratops, but also Psittacosaurus. The Psittacosaurus skull illustrates some of the traits that set ceratopsians apart: a rostral bone and narrow beak; a vaulted palate at the front of their mouth; and extended jugals or cheeks (see illustrations).

At the next level down on the taxonomic chart, Psittacosaurus splits into its own group, leaving all other ceratopsians in a group known as neoceratopsians (Triceratops, Torosaurus, Monoclonius, etc.) Seven species of Psittacosaurus are known from the Early Cretaceous formations of eastern Asia. All of these species are distinctively psittacosaurs: their snouts are short with nostrils that are set high and to the front; the rostrum is tall and parrot-like; the digits (fingers) on the forelimbs are reduced to three functional ones; and, lastly, the bony frill at the back of the head is hardly developed and barely visible.

In many ways Psittacosaurus skeletons resemble a very primitive ornithischian (like Heterodontosaurus and Hypsilophodon) rather than a ceratopsian. The hind limbs are longer than the front limbs; it probably walked on two legs and used its "hands" for holding plants as it browsed. Psittacosaurus had a moderately long, outstretched tail that was held in place by strong tendons along its spine. Psittacosaurs were common and widespread in their day and are an excellent example of a primitive ancestor to the extraordinary neoceratopsians that were to follow.

Anatomy

It is very interesting to compare the skull of Psittacosaurus with its later relatives like Triceratops--you can see many of the features, though painted with a smaller brush. Ther beak is clearly visible, as is the beginning jugal hornlet below and behind the eyes.

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