Redescription of the skull of Hezhengia bohlini (Artiodactyla, Mammalia) and a reassessment of the systematics of the Chinese late Miocene 'ovibovines'

摘要

Hezhengia is the most recently named 'ovibovine' genus, established by Qiu et al. (2000) based on a brief description of several skulls from Hezheng County, Linxia Prefecture, without attempting to provide a phylogenetic analysis with the other Chinese 'ovibovines', including Tsaidamotherium, Shaanxispira, Lantiantragus, Urmiatherium and Plesiaddax. Since then more than 100 well-preserved skulls have been discovered from the Linxia Basin. Most of the late Miocene 'ovibovines' have a highly specialized horn apparatus, and their inter-relationships and relationships to the extant Ovibos remain enigmatic. In this study, we provide detailed descriptions of H. bohlini skulls and mandibles, compared with the other Chinese late Miocene 'ovibovines'. Two previously described upper jaws (?Plesiaddax minor) from Fugu County in north-western China are referred to a second species of Hezhengia, H. minor (Bohlin, 1935a). We perform a cladistic analysis using 110 morphological characters of skull, teeth and horn core, including all the Chinese late Miocene 'ovibovine' genera with relatively complete skulls, the middle Miocene fossil bovid Turcocerus, and 13 extant bovids. An analysis focused on the target fossil taxa is also performed with minimally necessary extant bovids. The phylogenetic analyses indicate that the Chinese late Miocene 'ovibovines' are paraphyletic offshoots of the same Glade including Turcocerus and the extant capines, and none of them is closely related to Ovibos. We tentatively divided them into three groups, referring Hezhengia, Plesiaddax and Urmiatherium to the tribe Urmiatheriini, finding Shaanxispira and Lantiantragus as closely related, and Tsaidamotherium probably a distant Glade.