"Psittacosaurus" was first described as a genus in 1923, by Henry Fairfield Osborn. He named the type species "P. mongoliensis", for the location of its discovery in Mongolia, placing it in the new family Psittacosauridae. 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, Wong, found the type specimen (AMNH 6254), which preserves a nearly complete skull, as well as a post cranial skeleton lacking sections of the limbs. 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 mya. 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 long, to very old adults reaching nearly in length.