A new species of Brontotheriidae from the Middle Eocene of Junggar Basin, Xinjiang, China

摘要: A new species of large Irdinmanhan brontothere, Epimanteoceras mae sp. nov., is described based on an incomplete skull which was collected from the 躴bulak Formation of Sangequan site, Junggar Basin of Xinjiang Uygur Autonomous Region. The new specimen can be assigned to the genus Epimanteoceras by the large superorbital processes, the broad frontal bone, the shallow central fossae on the molars, and the absence of the anterolingual cingular cusp on molars and the hypocone on M3. E. mae is characterized by the slightly laterally bowed zygomatic arches, the medially arched parasagittal ridges, the posteromedially angled external auditory pseudomeatus, and the prominent occipital pillar processes. E. mae and E. formosus are closely related. It is uncertain whether E. mae or E. formosus forms the sister group to Brontotheriina, but both of them are the basal group of the latter in the phylogenetic analysis. They are both closed to the Irdinmanhan brontothere Protitan grangeri from Nei Mongol but much primitive than Aktautitan hippopotamopus from Kazakhstan. The discovery of E. mae in Sangequan indicates that the age of 躴bulak Formation is Middle Eocene, and earlier than that of Kyzylbulak Formation bearing A. hippopotamopus in Kazakhstan. Moreover, the discovery of E. mae in Xinjiang expanded the distribution of the genus Epimanteoceras, which was only found in Nei Mongol previously.