Large mammals evolved in highlands of the Himalayas and adapted a cold environment even before the beginning of the Ice Age, according to scientists.
Extra-large Ice Age fauna, best exemplified by the woolly mammoths and rhinos, have long been known for their adaptations to cold environments, such as large body size, long hair and snow-sweeping structures. These are the traits that were assumed to have evolved as result of the ice sheet expansion. But a new Pliocene mammal assemblage from a high-altitude basin in the western Himalayas, including a primitive wooly rhino, has a different story to tell.
An artist's reconstruction of a newly discovered species of Tibetan woolly rhino with a flattened horn. Photo: Julie Naylor
Paleontologists from the Natural History Museum of Los Angeles County and the Chinese Academy of Science discovered a 3.6 million-year-old fossil of a woolly rhinoceros high on the Tibetan Plateau in 2007. Based on the new fossils, they argue that some mega-herbivores first evolved in Tibet even before the beginning of the Ice Age. The fossil is believed to be the oldest sample of its kind ever discovered.
The cold winters in high Tibet served as a habituation ground for the mega-herbivores, which became pre-adapted for the Ice Age, successfully expanding to the Eurasian mammoth steppe, researchers said.
Equipped with a flat shovel-like horn, which it would have used to sweep away snow and find vegetation, the rhino, scientists estimate, was roughly the size of today's Indian and black rhinos. But since the fossils did not include hair, paleontologists can only guess how woolly it might have been.
Digital composite photo of the skull and lower jaw of the woolly rhino. Courtesy of Xiaoming Wang
The rhino's skull, unearthed by scientists, is 3 feet long and is believed to have belonged to a giant animal that weighed 1.2 to 1.4 tons, said study author Xiaoming Wang, a curator of vertebrate paleontology at the Natural History Museum of Los Angeles.
The rhino, dubbed as Coelodonta thibetan, also had teeth with high crowns, which could have made it easy for it to handle tough and high-altitude vegetation. Scientists suspect that the giant spread to northern Asia and Europe after the Ice Age set in 2.6 million years ago.
The extinction of Ice Age giants such as woolly mammoths and rhinos, giant sloths, and saber-tooth cats has been widely studied, but much less is known about where these giants came from, the researchers said in a statement. The Tibetan Plateau may have been another cradle of the Ice Age giants.
The findings of the study, released on Friday in the journal Science, also included vanished species of three-toed horse, Tibetan bharal (also known as blue sheep) and almost 25 other kinds of mammals.
Scientists expect that chilly places like Tibet, the Arctic and Antarctic are the hotspots where the most unexpected discoveries will be made in the future.