The frosty highlands of the Tibetan Plateau may have been an evolutionary cradle for woolly rhinos and other shaggy, cold-hardy creatures that roamed North America and Eurasia during the last Ice Age, according to a new study in Science.
The 2 September report describes fossils from an ancient species of woolly rhino that was roaming the Zanda Basin on the Tibetan Plateau 3.7 million years ago, sweeping snow out of its way with an elongated face and massive nasal horn.
It's generally been thought that the "megaherbivores" of the Pleistocene, such as woolly rhinos, evolved from less cold-tolerant ancestors in North America and Eurasia, developing adaptations to chilly conditions as the climate cooled there.
But the new fossils, described by Tao Deng of the Chinese Academy of Sciences in Beijing and colleagues, suggest that at least some of these animals may have gotten their start in high-altitude havens such as Tibet, where they honed cold-weather adaptations before expanding their range across Eurasia.
After analyzing the fossil's age and physical features, the researchers conclude that this new species of rhino, Coelodonta thibetana, was a relatively primitive ancestor in the woolly rhino family tree, compared to its counterparts in the later Pleistocene Epoch.
This finding suggests that the rhinos first adapted to the cold Tibetan Plateau well before climate change occurred in other areas, and that C. thibetana was thus poised for expansion into the rest of Asia as the climate cooled.
"When the Ice Age eventually came, it was able to descend from Tibet and expand to the rest of Eurasia," said Xiaoming Wang, a co-author on the Science paper from the Natural History Museum of Los Angeles County in California.
The authors similarly describe several other large animal fossils from the Zanda Basin, including a snow leopard, blue sheep, and Tibetan antelope, that were adapted to the cold. This region may thus have been the springboard for a variety of cold-hardy species that expanded their ranges during the Ice Age.
Wang said there have already been genetic studies that have traced possible links between the argali, a wild sheep on the Tibetan Plateau, and North American bighorn sheep, as well as the Tibetan wild yak and North American and European bison.
Wang, who has been working at paleontological sites in Tibet since 1998, said there are unique challenges to working at high altitude among the foothills of the Himalayan mountains. "You are short of breath, and physical exertion is that much more for the lack of oxygen."
Still, he called the Zanda Basin "one of the most wonderful places in the world" to work, and he is optimistic that there is much more to uncover in Tibet.
"Cold places, such as Tibet, Arctic, and Antarctic, are where the most unexpected discoveries will be made in the future," he said. "These are the remaining frontiers that are still largely unexplored."
Author: Kathy Wren | Source: American Association for the Advancement of Science [September 01, 2011]
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| This artist's rendering shows a wooly rhino using its flattened horn to sweep snow away in order to find vegetation for food. A 3.6-million-year-old woolly rhinoceros fossil discovered in Tibet indicates that some giant mammoths, sloths and saber-tooth cats may have evolved in highlands before the Ice Age, experts say [Credit: DENG Tao] |
It's generally been thought that the "megaherbivores" of the Pleistocene, such as woolly rhinos, evolved from less cold-tolerant ancestors in North America and Eurasia, developing adaptations to chilly conditions as the climate cooled there.
But the new fossils, described by Tao Deng of the Chinese Academy of Sciences in Beijing and colleagues, suggest that at least some of these animals may have gotten their start in high-altitude havens such as Tibet, where they honed cold-weather adaptations before expanding their range across Eurasia.
After analyzing the fossil's age and physical features, the researchers conclude that this new species of rhino, Coelodonta thibetana, was a relatively primitive ancestor in the woolly rhino family tree, compared to its counterparts in the later Pleistocene Epoch.
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| A, Skull and cheek teeth of Coelodonta thibetana. B, Origin, distribution, and dispersal of woolly rhinos in Eurasia [Image by DENG Tao] |
"When the Ice Age eventually came, it was able to descend from Tibet and expand to the rest of Eurasia," said Xiaoming Wang, a co-author on the Science paper from the Natural History Museum of Los Angeles County in California.
The authors similarly describe several other large animal fossils from the Zanda Basin, including a snow leopard, blue sheep, and Tibetan antelope, that were adapted to the cold. This region may thus have been the springboard for a variety of cold-hardy species that expanded their ranges during the Ice Age.
Wang said there have already been genetic studies that have traced possible links between the argali, a wild sheep on the Tibetan Plateau, and North American bighorn sheep, as well as the Tibetan wild yak and North American and European bison.
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| A, Phylogenetic position of Coelodonta thibetana. B and C, Enamel δ13C and δ18O values of herbivores in Zanda. D-F, three large mammals from Zanda fauna: D, Blue sheep; E, Snow leopard; F, Tibetan antelope [Image by DENG Tao] |
Still, he called the Zanda Basin "one of the most wonderful places in the world" to work, and he is optimistic that there is much more to uncover in Tibet.
"Cold places, such as Tibet, Arctic, and Antarctic, are where the most unexpected discoveries will be made in the future," he said. "These are the remaining frontiers that are still largely unexplored."
Author: Kathy Wren | Source: American Association for the Advancement of Science [September 01, 2011]
