New materials of Pliorhinus ringstroemi from the Linxia Basin (Late Miocene, eastern Asia) and their taxonomical and evolutionary implications

A large collection of dicerorhine rhinoceros remains, here identified as Pliorhinus ringstroemi, were studied from the Late Miocene deposits of the Linxia Basin, eastern Asia. The new specimens include several complete skulls with for the first-time preserved premaxillae, providing new knowledge on the morphology and allowing a preliminary investigation of the intraspecific variation of the species. The morphological study supports Pliorhinus ringstroemi as a valid species and phylogenetic analyses place it as the sister group of P. megarhinus and P. miguelcrusafonti. Compared with P. megarhinus, the unique characters of P. ringstroemi include the better developed and oval I1, tusk-like i2, complex secondary folds on upper cheek teeth, convex base of the mandibular corpus, and slightly different skull shape as supported by the geometric morphometric study. Our findings confirm the gradual reduction of incisors, elongated nasal, retracted nasal notch, and, finally, a developed bony nasal septum previously reported for Dicerorhina. The early age and primitive traits suggest that Pliorhinus could have originated in Asia and migrated to Europe at the latest Miocene, taking the niche of closely related species Dihoplus pikermiensis in Europe.