June 11, 2014
High Tibet May Have Been Starting Point For Cold-Adapted Mammals
Gerard LeBlond for www.redorbit.com - Your Universe Online
Over the past 2.5 million years, the Earth has gone through changes in climate. Warm and cold cycles, some lasting for millennia, have become known as the Ice Age. During the cold cycles, ice sheets covered large areas of the northern hemisphere and as the ice melted during the warm cycles, the glaciers receded leaving huge valleys behind. These cycles also affected the evolution and distribution of animals, including the ones living in cold climates today.
Fossil specimens were discovered in the Zanda Basin in southern Tibet in 2010.
Along with lead author of the paper Xiaoming Wang, from the Natural History Museum of Los Angeles County (NHM), the team included co-authors Zhijie Jack Tseng of the University of Southern California, Qiang Li of the Chinese Academy of Sciences, Gary T. Takeuchi of Page Museum at the La Brea Tar Pits, and Guangpu Xie of Gansu Provincial Museum.
Among the fossils unearthed, were the Arctic fox, extinct species of a woolly rhino, three-toed horse, blue sheep, Tibetan antelope, snow leopard, badger and 23 other mammals. Cold-adapted mammals had been previously thought to have originated from the Arctic tundra or other cool regions. However, this new study suggests some of the Ice Age animals, including North America’s woolly mammoth, saber-toothed cat, giant sloths and others, pre-adapted to the colder climates of the Ice Age 2.6 million years ago.
Wang says the location is a grueling but rich area for paleontological fieldwork. His team, over the last 15 summer seasons, has had good success on their expeditions. They involve a one-week journey to Lhasa, then a four-day drive to the “layer cake” sediments of the Zanda Basin. The team camps at more than 14,000 feet where the water freezes overnight and it is difficult to breathe. Every morning the team searches for fossils.
Most of the fossils are found in ancient lake margins. To keep up their strength and stamina, the team alternates camp nights with nights in town. “There are a lot of challenges, but in paleontological terms, it is a relatively unexplored environment. Our efforts are rewriting a significant chapter of our planet's recent geological history,” Wang said.
Image 2 (below): Pliocene Tibetan fox localities (red stars); Ice Age arctic fox (yellow); and today's arctic fox. Credit: Xiaoming Wang