Psittacosaurus Sinensis
In the 1950s, a new Chinese species of Psittacosaurus was found in the Aptian-Albian Qingshan Formation of Shandong Province, southeast of Beijing. C.C. Young called it Psittacosaurus sinensis to differentiate it from P. mongoliensis, which had originally been found in Mongolia. Fossils of more than twenty individuals have since been recovered, including several complete skulls and skeletons, making this the most well-known species after P. mongoliensis.
P. sinensis is readily distinguished from all other species by numerous features of the skull. Adult skulls are smaller than those of P. mongoliensis and have less teeth. Uniquely, the premaxillary bone contacts the jugal (cheek) bone on the outside of the skull. The jugals flare out sideways, forming 'horns' proportionally wider than in any other known Psittacosaurus species except P. sibiricus and P. lujiatunensis. Because of the flared cheeks, the skull is actually wider than it is long. A smaller 'horn' is present behind the eye, at the contact of the jugal and postorbital bones, a feature also seen in P. sibiricus. The mandible (lower jaw) lacks the hollow opening, or fenestra, seen in other species, and the entire lower jaw is bowed outwards, giving the animal the appearance of an underbite. The skull of an adult P. sinensis can reach 11.5 centimeters (4.5 in) in length.
Read more about this topic: List Of Psittacosaurus Species