Rhinocerotoid fossils of the Linxia Basin in northwestern China as late Cenozoic biostratigraphic markers

Abstract

This study reports on rhinocerotoid fossils from the Oligocene-Pleistocene strata of the Linxia Basin of Gansu Province, northwestern China. Rhinoceroses have been important components of mammalian faunas of these beds, and include the Late Oligocene giant rhinos (paraceratheres) and the Late Miocene hornless rhinos (aceratheres). As a result of their high diversity, wide geographical distribution and rapid evolution, rhinoceroses are good markers for stratigraphic division and may be used for intercontinental correlations. The Late Oligocene fauna of the Linxia Basin occurs in the lower part of the Jiaozigou Formation. Among 12 species of large mammal fossils, nine are of the superfamily Rhinocerotoidea, and giant rhinos are dominant. Rhinoceroses of the Middle Miocene fauna reflect a forest environment. Comparison with contemporaneous European rhinoceroses suggests a dispersal route for populations along the north side of the Tibetan Plateau. Rhinoceroses were most abundant in the Linxia Basin in the Late Miocene times. The most primitive species of the genus Chilotherium and the huge elasmotheres are key indicators for the base of the Upper Miocene (Tortonian). From the Late Miocene to Early Pliocene, the assemblages of the three-toed horse Hipparion comprise five horizons, each of which has different rhinocerotid fossils as markers of division and correlation. Because of the strong competition by ruminants, rhinoceroses declined greatly in the Early Pleistocene fauna. At that time, only a species of the woolly rhino persisted, but as an intermediate form, Coelodonta nihowanensis of the Linxia Basin can still connect the Pliocene Zanda Basin of the Tibetan Plateau and the Early Pleistocene Nihewan Basin of the North China Plain.