A new species of Urmiatherium (Bovidae, Mammalia) from the Late Miocene of China and its implications for cranial evolution in ovibovin-like bovids

Late Miocene ovibovin-like bovids are characterized by specialized cranial morphology associated with reinforced cranio-cervical articulations. Among them, Urmiatherium is one of the most derived genera, yet the evolutionary sequence of its cranial specializations remains poorly understood. Here, we describe Urmiatherium cheni, sp. nov. from the Late Miocene of northern China based on multiple crania, associated dentitions, and cervical vertebrae. Morphological comparisons with other Urmiatherium species were conducted to assess cranial and dental evolution within the genus. Urmiatherium cheni differs from previously known species in its relatively small body size, narrow braincase, moderate frontal inflation and exostoses, and less specialized basioccipital morphology. The horn apparatus represents an intermediate condition between the primitive Urmiatherium kassandriensis and the more derived Urmiatherium polaki and Urmiatherium intermedium. Comparisons among species indicate a general evolutionary trend involving frontal inflation, expansion of cranial exostoses, and reinforcement of the basioccipital and cervical articulation system, whereas body size shows no clear directional trend. Some cranial features traditionally regarded as diagnostic for ovibovin-like bovids, including the flattened parieto-occipital angle and thickened basioccipital, may reflect structural constraints associated with cranial loading rather than stable phylogenetic characters. The new material provides new evidence for cranial evolution and functional specialization among Late Miocene ovibovin-like bovids.