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 "P. 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". Chinese paleontologist Zhao Xijin named a new species after his mentor, C. C. Young, in 1962. However, the type specimen of "P. youngi" (a partial skeleton and skull) was discovered in the same rocks as "P. sinensis" and appears to be very similar, so "P. youngi" is generally considered a junior synonym of that better-known species. As with "P. guyangensis" and "P. osborni", You and Dodson (2004) listed it as valid in a table, but not in their text.