A new species of Lophiomeryx from the Eocene of Bujiamiaozi (Ningxia, China) and implications for the early evolution of the family Lophiomerycidae

The evolutionary history of the Lophiomerycidae, an early ruminant group from the Palaeogene of Eurasia, remains poorly understood. In this study we describe a new taxon, Lophiomeryx zongi sp. nov., from the middle Eocene of northern China. This new species is characterized by its small size (the smallest in the genus Lophiomeryx ), a long p1–p2 diastema that approximately equals the c–p1 length, a long posthypoconulidcristid that lingually closes the m3 back basin, and the relatively strong M1 cingulum. Cladistic analysis suggests that the Lophiomerycidae can be divided into two monophyletic groups: a ‘northern clade’ and a ‘southern clade’. The northern clade includes all species of Lophiomeryx , which lived in drier environments during the middle and late Eocene in northern China and subsequently dispersed across Eurasia during the Oligocene. In contrast, the southern clade, which includes Zhailimeryx , Krabimeryx and Chiyoumeryx , lived in the middle and late Eocene of southern China and Southeast Asia under wetter conditions until the onset of the Oligocene after the Terminal Eocene Event. Our findings provide new insights into the evolution and diversity of Lophiomerycidae and help to resolve ongoing debates on the phylogenetic relationships within the family.