AsianScientist (May 19, 2016) – The modern wild sheep, Ovis, is widespread in mountain ranges around the world. In Eurasia, ancient sheep fossils have been found at a few Pleistocene sites in North China, eastern Siberia, and western Europe, but are so far absent from the Tibetan Plateau. Now, an international team of researchers have reported a new genus and species of fossil sheep from the Pliocene of Zanda Basin in Tibet.
The research team, led by paleontologists from the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) of the Chinese Academy of Sciences, published their discovery in the Journal of Vertebrate Paleontology.
This finding extends the fossil record for the sheep into the Pliocene of the Tibetan Plateau, and suggests that the Tibetan Plateau, possibly including Tianshan-Altai, represents the ancestral home range(s) of mountain sheep. It is also possible that these basal stocks were the ultimate source of all extant species.
“With the present discovery of a primitive sheep in the Himalayas, we thus offer another example of our previous out-of-Tibet hypothesis—ancestral sheep were adapted to high-elevation cold environments in the Pliocene, and during the Pleistocene they began to disperse outside their ancestral home range in Tibet to northern China, northern Siberia, and western Asia,” said Dr. Wang Xiaoming, a visiting professor at IVPP and a senior curator of the Natural History Museum of Los Angeles County.
The fossils were collected from the Tibetan Autonomous Region in the Western Himalayas during the 2006 and 2007 field seasons. The holotype specimen, forming the main basis of this new species, comprises nearly complete male left and right horncores. With a total horncore upper curve length of 443 mm, it is similar in size to some extant species of Ovis.
The fossil sheep, Protovis himalayensis, has a combination of features distinguishable from other species such as Ovis, Pseudois and Tossunnoria. Smaller than the living argali, or mountain sheep, it shares with Ovis posterolaterally arched horncores and partially developed sinuses, and possesses several transitional characters leading to Ovis.
Situated between the Himalayas and Ayilariju ranges, the Zanda Basin was formed in a tectonically active region. Along the shores of the paleo-Zanda lake, basement outcrops from residual topography and surrounding mountains offered plenty of rugged terrain and gentle hills. The environment occupied by Protovis is not far from one of the paleo-islands formed by metamorphic basement rock, and these cliffs probably provided protection from predators in times of danger.
Ancestral sheep in the Tibetan Plateau, occupying a similar range as the extant argali, were adapted to high-elevation, cold environments during the Pliocene, when conditions elsewhere (including the high Arctic regions) were much warmer.
By the time the Ice Age arrived around 2.6 million years ago, Ovis possessed a competitive advantage for surviving in freezing environments and spread rapidly to regions surrounding the Plateau and beyond. Most sheep species survived along their Pleistocene route of dispersal, the authors say.
“Fortunately, wild sheep were able to take refuge in mountain ranges, possibly an important contributing factor in protection against early human hunting, and they have largely survived the end-Pleistocene extinction that befell many of their megafaunal contemporaries,” said study coauthor Dr. Li Qiang.
The article can be found at: Wang et al. (2016) Out of Tibet: an Early Sheep from the Pliocene of Tibet, Protovis himalayensis, Genus and Species Nov. (Bovidae, Caprini), and Origin of Ice Age Mountain Sheep.
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Source: Chinese Academy of Sciences; Photo: Julie Selan and Wang Xiaoming.
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