Perissodactyl diversities and responses to climate changes as reflected by dental homogeneity during the Cenozoic in Asia

Cenozoic mammal evolution and faunal turnover are considered to have been influenced and triggered by global climate change. Teeth of large terrestrial ungulates are reliable proxies to trace long term climatic changes due to their morphological and physico-chemical properties; however, the role of premolar molarization in ungulate evolution and related climatic change have rarely been investigated. Recently, three patterns of premolar molarization among perissodactyls have been recognized: endoprotocrista-derived hypocone (Type I); paraconule-protocone separation (Type II); and metaconule-derived pseudohypocones (Type III). These three patterns of premolar molarization play an important role in perissodactyl diversity coupled with global climate change during the Cenozoic in Asia. Those groups with a relatively higher degree of premolar molarization, initiated by the formation of the hypocone, survived into Neogene, whereas those with a lesser degree of molarization, initiated by the deformation of existing ridges and cusps, went extinct by the end of the Oligocene. In addition, the hypothesis of the “Ulan Gochu Decline” is proposed here to designate the most conspicuous decrease of perissodactyl diversity that occurred in the latest middle Eocene rather than at the Eocene-Oligocene transition in Asia, as conventionally thought; this event was likely comparable to the contemporaneous post-Uintan decline of the North American land fauna.