In 1923 through 24, Osborn described two small dinosaurs found at the Oshih Nur locality.He believed the two belong to different ornithopods and therefore designated two new taxa, Psittacosaurus mongoliensis and Protiguanodon mongoliensis. Osborn also pointed out that the first one was the ancestor of Protoceratops , and the latter was related to iguandonts.
In 1958, C. C. Young studied fossil remains of Psittacosaurus sinenesis “from the Laiyang Basin of the Shandong Province. He concluded that the two taxa above, designated by Osborn, represent in fact the same species, Psittacosaurus mongoliensis. In the 1970s, H.Osmolska and T. Maryanska pointed out that Psittacosaurus possessed a rostral bone, the unique feature of all ceratopsians. As a consequence of this finding, psittacosaurids have been associated with the ceratopsian clade.
Psittacosaurus had a prominent parrotlike beak, the structure, which provided reasons to name these dinosaur as “parrot-lizard” .Psittacosaurus used the beak to chop vegetation.The food was later pulverized by gizzard stones, found within skeletal remains surrounding the area of lost visceral organs. Although widely distributed, Psittacosaurus was restricted only to prehistoric Asia.Nine species referred to the Psittacosaurus genus were described, most of them very recently.