The comparative anatomy of the petrosal bone and bony labyrinth of four small-sized deer.

Here we provide complete 3D reconstructions of the petrosal bone and bony labyrinth of four kinds of small-sized deer (Elaphodus cephalophus, Muntiacus reevesi, Muntiacus muntjak, Hydropotes inermis) based on high-resolution CT scanning, and select one musk deer (Moschus moschiferus) as a comparative object. The petrosal bone and bony labyrinth of E. cephalophus are illustrated for the first time, as well as the petrosal bones of M. reevesi and H. inermis. Some morphological characters of petrosal bone and bony labyrinth can be used to distinguish the above-mentioned species. For example, M. moschiferus shows a prominent transpromontorial sulcus and a ventral basicapsular groove on the petrosal bone; there is a bifurcate cochlear aqueduct on the bony labyrinth of E. cephalophus; there is a distinct fusion between the lateral and posterior semicircular canals on the bony labyrinth of H. inermis. Meanwhile, there are some intraspecific variations on the subarcuate fossa, the tegmen tympani, the cochlear aqueduct, as well as the endolymphatic sac. Our results further confirm that the petrosal bone and bony labyrinth have enormous potential for taxonomy. This work will provide new anatomical data for the phylogenetic study of ruminants in the future, and it will be very practical to identify the isolated ruminants' petrosal bones that are frequently unearthed from paleontological or archeological sites.