New fossils of Bison palaeosinensis (Artiodactyla, Mammalia) from the steppe mammoth site of Early Pleistocene in Nihewan Basin, China

Since the establishment of the species Bison palaeosinensis by Teilhard de Chardin and Piveteau in 1930, no new fossils have been reported in the last few decades. Recent excavations at the Shanshenmiaozui site in Nihewan Basin of North China led to the discovery of numerous Bovini fossils, including a nearly complete mandible and articulated postcranial bones. The stout axis and the protruded mandibular angle, thick posterior rim of the mandibular ramus, prominently curved coronoid process, thickened mandibular symphysis and short dentition support an assignment to the Bison genus. Moreover, the new specimens have smaller and proportionally narrower cheek teeth as well as a higher premolar to molar ratio than those found in later forms of bison, further supporting their assignment to the species Bison palaeosinensis. The postcranial bones are also considerably smaller and more slender than those of the later forms of bison. In North China, isolated teeth and postcranial bones have contributed to confusion regarding the distinction between early bison and Leptobos, because these specimens have similar dimensions and were temporally concurrent even at the same site. In addition, sexual dimorphism is another potential factor making identification work difficult. In Nihewan Basin, the joint occurrence of Bison palaeosinensis with Mammuthus trogontherii and Coelodonta nihowanensis marks the appearance of the early stage of the Mammuthus-Coelodonta faunal complex.