List of Psittacosaurus Species - Psittacosaurus Mongoliensis (type)

Psittacosaurus Mongoliensis (type)

Psittacosaurus mongoliensis is the type species of the genus, named by American paleontologist Henry Fairfield Osborn in 1923. Remains of this dinosaur were first discovered the year before, on the third American Museum of Natural History expedition to the Gobi Desert of Mongolia, when one of the expedition's drivers found the type specimen (AMNH 6254). This same expedition turned up the remains of many other famous Mongolian dinosaurs, including Protoceratops, Oviraptor, and Velociraptor. Many later expeditions by various combinations of Mongolian, Russian, Chinese, American, Polish, Japanese, and Canadian paleontologists also recovered specimens from throughout Mongolia and northern China. In these areas, Psittacosaurus mongoliensis fossils are found in most sedimentary strata dating to the Aptian to Albian stages of the Early Cretaceous Period, or approximately 125 to 100 Ma (million years ago). Fossil remains of over 75 individuals have been recovered, including nearly 20 complete skeletons with skulls. Individuals of all ages are known, from hatchlings less than 13 centimeters (5 in) long, to very old adults reaching nearly 2 meters (6.5 ft) in length.

Skulls of P. mongoliensis are flat on top, especially over the back of the skull, with a triangular depression, the antorbital fossa, on the outside surface of the maxilla (an upper jaw bone). A flange is present on the lower edge of the dentary (the tooth-bearing bone of the lower jaw), although it is not as prominent as in P. meileyingensis or P. major. P. mongoliensis is among the largest known species. The skull of the type specimen, which is probably a juvenile, is 15.2 centimeters (6 in) long, and the associated femur is 16.2 centimeters (6.4 in) in length. Other specimens are larger, with the largest documented femur measuring about 21 centimeters (8.25 in) long.