New study sheds light on the impressive intraspecific variation of Quaternary Asiatic black bears in China

Abstract

Asiatic black bears have long been recognized as key members of the Quaternary mammalian fauna in South China. Despite this, for decades, taxonomic remarks since the Early Pleistocene Ursus thibetanus have been controversial, and the intraspecific variations of it remain unresolved. We here described a nearly complete black bear skull from the late Mid-Pleistocene or the early Late-Pleistocene (ca. 134 ± 22–133 ± 30 ka) of the Sifangdi Cave, Yanjinggou area, Chongqing. The studied material was compared with other U. thibetanus materials from the Quaternary localities in China.Morphological analyses revealed impressive intraspecific variations and that U. t. kokeni can be deemed as an invalid paleosubspecies, which discernibly corresponds to all living subspecies of U. thibetanus. Based on isolated teeth and several skulls from various localities, we proposed that U. thibetanus primitinus was a black bear with small-sized skull and upper molars, while U. thibetanus since the Mid-Pleistocene was a larger black bear with significantly larger cranium and upper molars, in accordance with extant subspecies. Furthermore, in response to the prominent Mid-Pleistocene climate transition and ecosystem changes, it is evident that black bears tend to have increased their body sizes, expanded their living territories, and perhaps even arrived at the localities in North China since the Mid-Pleistocene.