New fossils of sambar (Rusa unicolor) from Bailong Cave, a Middle Pleistocene human site in Hubei, China

The sambar (Rusa unicolor) is among the main elements of the Oriental Realm. The sambar fossils unearthed from Bailong Cave site dated back to the Middle Pleistocene were better preserved than those from any other fossil site. We described these remains especially focusing on the deciduous teeth and petrosal bone as well as the bony labyrinth which have never been studied before. The measurements of antler and cheek teeth fall within the range of intraspecific variations of extant specimens. The sambar's antler and cheek teeth differ from other allied cervids in having more rugose three-tined antlers, thicker enamel of cheek teeth, and in possessing tapered entostyles on upper molars and stout anterior ectostylid on dp4. The petrosal bone is similar to that of the extant sambar in 3D reconstructions, but different from those of Cervus nippon and Axis axis. The differences are mainly related to the size and overall shape of petrosal bone as well as the dorsolateral outline of tegmen tympani. There are variations in the shape of internal acoustic meatus and subarcuate fossa as well as the position of hiatus Fallopii between extant and fossil sambar specimen. The bony labyrinth of sambar resembles that of Javan deer (Rusa timorensis), while the shape of endolymphatic sac of sambar is paddle-like instead of funnel-like as in R. timorensis. R. unicolor maybe originated from southern China during Mid-Pleistocene Transition, and we provisionally regard Rusa yunnanensis rather than Rusa elegans as the direct ancestor of sambar based on the morphological characters of antler and tooth.