A new elasmothere (Perissodactyla, Rhinocerotidae) from the late Miocene of the Linxia Basin in Gansu, China

Ningxiatherium euryrhinus sp. nov. is a relatively large elasmothere rhino from the Linxia Basin in northwestern China found in the early Bahean, which corresponds to the early Vallesian (MN 9), ca. 11.1 Ma. It is much larger than the extant Ceratotherium simum and has a single horn. Ningxiatherium is similar to the late Miocene Parelasmotherium from Gansu and Shanxi, but differs in having partially ossified nasal septum, terminal nasal horn boss, shallower nasal notch above the P3/P4 boundary, and much shorter premolars. N. euryrhinus sp. nov. differs from N. longirhinus from the late Miocene of Zhongning, Ningxia in northwestern China by its larger size, relatively wider nasals, shallower nasal notch, and sub-quadrangular occlusal surface of M3. In the Linxia Basin, the other early late Miocene (Bahean or Vallesian) elasmotheres are known from complete skulls or isolated teeth. They include two genera and three species: Parelasmotherium linxiaense, P. simplum, and Iranotherium morgani. They lack a nasal septum, but Ningxiatherium has one. The age of N. euryrhinus is early late Miocene based on direct association with biochronologic indicator taxa, such as Dinocrocuta gigantea, Hipparion dongxiangense, and Chilotherium primigenius. N. euryrhinus is more primitive than N. longirhinus sp. nov. in having a sub-quadrangular M3, a shallower nasal notch, and the presence of DP1 in adults.