The giant short-faced hyena Pachycrocuta brevirostris (Mammalia, Carnivora, Hyaenidae) from Northeast Asia: A reinterpretation of subspecies differentiation and intercontinental dispersal

The giant short-faced hyena, Pachycrocuta brevirostris, was the largest and most spectacular bone-cracking hyena that ever existed. Although already extinct long ago, it was extensively distributed across Eurasia during the Early and Middle Pleistocene. P. brevirostris is remarkable for a series of iconic craniodental adaptations in sway with a commitment to scavenging off carcasses of other large herbivores, such as the powerfully built skull and massive premolars, yet the most eye-catching aspect is the enormous size as emphasized by its vernacular name. The largest hitherto known skull of this species is the holotype from Sainzelles in Auvergne, France, discovered over a century ago. We hereby report a new discovery from Jinyuan Cave in Dalian, China, which slightly surpasses the holotype in craniodental dimension, posing a new record in Pachycrocuta body size. Three skull fragments of the same individual unearthed from the site are described in detail herein and compared with other P. brevirostris discoveries from both Europe and Asia. Thorough comparative studies show that the newly discovered materials are very close to the holotype from Sainzelles both metrically and morphologically, which fully indicates that the European morphotype, namely Pachycrocuta brevirostris brevirostris, surprisingly appeared in Northeast Asia as well, and further challenges the conventional concept of the population or subspecies. The giant hyenas from Asia were originally proposed as independent species, such as Pachycrocutalicenti or P. sinensis, but now broadly accepted as conspecifics of the European Pachycrocuta brevirostris, forming only different subspecies. The occurrence of P. b. brevirostris in Northeast Asia forcefully demonstrates that the differentiation is more of temporal than geographical significance, i.e., the subspecies of Eurasia basically constituted an ancestor-descendant sequence, from licenti to sinensis via brevirostris. Moreover, represented by the newly discovered specimens, the forerunner of P. b. brevirostris with transitional features appeared in Northeast Asia as early as 2.0 Ma, which implies the population of Europe most likely originated and dispersed from Northeast Asia. A hypothesis of “out of Northeast Asia” is hereby proposed for P. b. brevirostris. In the present paper, a series of diagnostic craniodental characters, such as carnassial morphology, the accessory cuspids of the premolars and the shape of the skull profile, are also discussed and re-valuated to investigate their potential significance in phylogenetic analysis.