Saturday 10 September 2011

A Woolly Rhino from the Pliocene of Tibet.

The Wooly Rhinoceros is an iconic member of the Pleistocene Ice Age megafauna, found across the Eurasian steppes from Scotland in the West to Korea in the East. They were thought to have first appeared in China at the start of the Pleistocene roughly 2.5 million years ago, and survived to as recently as 8000 years ago in parts of Siberia. Wooly Rhinos all belonged to a single genus, Coelodonta, distinguished by a thick wooly coat and a large flattened horn far forward on the snout, hypothesized to have been used for clearing snow in order to access grass and herbage.

Reconstruction of a Wooly Rhino, by Palaeontological Artist Mauricio Antón.

The 2 September edition of the journal Science contains a paper by a team lead by Tao Deng of the Institute of Vertebrate Paleontology and Paleoanthropology at the Chinese Academy of Sciences in which they announce the discovery of a new species of Wooly Rhino from the Pliocene of Tibet, roughly 3.7 million years ago - or at least 900 000 years before the onset of the first Pleistocene Glaciation. This suggests that rather than evolving as a response to the onset of glaciation, the Wooly Rhino, and possibly other Pleistocene megafauna, already existed on the frozen Tibetan Plateau and spread opportunistically across the rest of Eurasia with the onset of Glaciation.

The new species has been named Coelodonta thibetana, and is described from a single specimen, comprising the skull and first three vertebrae, found in the Zanda Basin in Western Tibet by Xiaoming Wang of the Natural History Museum of Los Angeles County during a 2007 expedition. It has the typical flattened, forward located horn of the genus, as well as high crowned, deeply hollowed teeth, which are also considered typical of the genus, but a nasal structure that is considered primitive compared to that of the rest of the genus.

Coelodonta thibetana, before it was separated from its rock matrix.

During the Middle to Late Pliocene the Zanda Basin is thought to have been a cold, upland environment, but much wetter than it is now. The site where the skull was discovered appears to have been a marshy environment associated with a river entering a lake in a broad delta. In addition to the Coelodonta skull the expedition also discovered the partial palate of a primitive giraffe, the skull of a horse, the tooth of a deer, and a toe bone from a rhino of the genus Dicerorhininae, the genus which includes the Sumatran Rhino, thought by the closest living relative of the Wooly Rhino, as well as numerous smaller mammals, and invertebrates.

Reconstruction of Coelodonta thibetana by illustrator Julie Naylor.