Xu Xing, another Chinese paleontologist, named a new species of "Psittacosaurus" in 1997, based on a complete skull with associated vertebrae and a forelimb. This material was recovered in Gansu Province, near the border with Inner Mongolia. This species is named "P. mazongshanensis" after the nearby mountain called Mazongshan (Horse Mane Mountain) and has been described in a preliminary manner. Unfortunately, the skull was damaged while in the care of the Chinese Institute of Vertebrate Paleontology and Paleoanthropology (IVPP), and several fragments have been lost, including all of the teeth. The remains were found in the Lower Xinminbao Formation, which have not been precisely dated, although there is some evidence that they were deposited in the late Barremian through Aptian stages. Sereno suggested in 2000 that "P. mazongshanensis" was a "nomen dubium", with no unique features that separate it from any other species of "Psittacosaurus". However, more recent authors have noted that it can be distinguished by its proportionally long snout compared to other species of "Psittacosaurus", as well as a prominent bony protuberance, pointing outwards and downwards, on the maxilla of the upper jaw. The maxillary protuberance is also now missing. Other features originally used to distinguish the species have been recognised as the results of the deformation of the skull after fossilisation. Sereno (2010) remained unconvinced of its validity.