New materials of Lophiomeryx (Artiodactyla: Lophiomerycidae) from the Oligocene of Nei Mongol, China

Fossil teeth representing four species of Lophiomeryx are identified from early Oligocene strata in the Saint Jacques area of Nei Mongol, including L. shinaoensis, L. gracilis, L. cf. chalaniati, and L. triangularis sp. nov. This represents the highest species richness of this early traguline from a single stratigraphic sequence. The new materials expand the spatiotemporal ranges of L. shinaoensis and L. gracilis, which are previously known from the late Eocene of Guizhou, south China. We present further morphological details that support the validity of the original taxonomy for the Guizhou materials. L. cf. chalaniati resembles the type species morphologically but is smaller than European specimens. L. triangularis sp. nov. is the last to appear in the sequence, and it is notably larger and more high-crowned than all the other known species of Lophiomeryx. Aside from the dental materials, we report the first known skull of L. gracilis, collected from a nearby locality, Qianlishan. While the overall skull morphology is primitive for tragulines, the specimen preserves a closed postorbital bar, a derived feature that was previously thought to be absent in Lophiomeryx. Our new specimens shed light on the diversity, biogeography, and ecology of this basal ruminant as well as on the evolution of early tragulines.