Ovis is a genus of artiodactyl mammals of the Bovidae family that includes the domestic sheep and several closely related wild species, such as the European mouflon or the uriales ( Ovis vignei ), a type of wild ram that inhabits the mountains of Russia, Afghanistan, Pakistan , India and several Central Asian countries. Modern wild sheep, all of the genus Ovis , are widely spread throughout the Caucasus and Himalayan ranges, the Tibetan Plateau, the Tianshan-Altai range, in Eastern Siberia, and also in the Rocky Mountains of North America. In Eurasia, fossil remains of the ancestors of this type of sheep have been found in a few Pleistocene sites in northern China, Eastern Siberia and Western Europe, but until now they have not been located on the Tibetan Plateau .
Recently, a team of paleontologists from the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) of the Chinese Academy of Sciences, the Los Angeles County Museum of Natural History and the La Brea Tar Pits and Museum, also in Los Angeles, California, have published in the Journal of Vertebrate Paleontology the find of fossils of a new genus and species of wild Pliocene sheep in the Zanda Basin , Tibet. This find extends the fossil record of the sheep to the Pliocene on the Tibetan Plateau, and suggests the possibility that this geographical area, which spans from Tibet to the Tianshan-Altai Mountains, represents the ancestral home of wild mountain sheep and of that it was the common origin of all the remaining extant species, which seems consistent with the hypothesis that the megaherbivores of the Ice Age came out of Tibet .
The new fossil materials were collected in Guanjingtai , Zanda County, Tibet Autonomous Region, west of the Himalayas, in the field work carried out in 2006 and 2007. The remains of the specimen IVPP V18928 on which the theory has been based that it is a new species are the almost complete horns of a male , similar in size to those of some existing species of Ovis . This new extinct sheep has been named Protovis himalayensis and brings together easily distinguishable combined traits from other species of Ovis , Pseudovis and Tossunnoria . Smaller than the current Argali or Asian mouflon, it shares postero- laterally arched horns with the Ovis and other characteristics that point to the transition to the Ovis .
Situated between the Himalayas and the Ayilariju region, the Zanda Basin was formed in a tectonically active zone that, as it developed geologically, created rolling terrain and gentle hills around Lake Zanda. Protovis’ original habitat must not have been far from some primitive islands formed by sediments of metamorphic rocks that probably offered them refuge from predators in times of scarcity and danger. Carbon evidence in herbivorous mammal fossils from the Zanda Basin indicates that vegetation and plants dominated the landscape during the Pliocene , and that they were likely part of the Protovis diet, similar to that of modern bovids of the Tibetan Plateau. .
These ancestral sheep from Tibet occupied an ecological niche similar to that of the current Argali, and adapted to the high altitude and cold environment of the Pliocene in that region, while in the rest of the planet at that time, even in the Arctic areas, the conditions were warmer. Then its morphology quickly evolved towards that of the current Ovis. When the Ice Age began 2.6 million years ago, the Ovis had competitive adaptive advantages by having lived in an environment much colder than other animals in surrounding regions.
PHOTO CAPTION: Artist’s reconstruction of the male Zanda sheep, Protovis himalayensis.
CREDIT: Art, Julie Selan. Background photo, WANG Xiaoming
