A couple horses: just horsing aroundCourtesy cone_dmn via FlickrA couple equine stories are in the news.

First, a new genetic study published in the Proceedings of the National Academy of Sciences has traced the mitochondrial genomes of modern horses to a single mare that lived about 140,000 years ago. According to the research team, eighteen different genetic lines radiated from that one horse. Evidence suggests domestication of horses by humans took place about 10,000 years ago during the early Neolithic Age, and occurred independently throughout the world.

The second horse tale reaches even farther back in equine ancestry and concerns the odd evolutionary behavior of a proto-horse named Sifrhippus sandrae. The cat-sized creature roamed the ancient landscape of Wyoming about 56 million years ago. A sudden warming trend known as the Paleocene-Eocene Thermal Maximum
caused the already midget equine to reduce its size even more - by about 30 percent - from 5.6 kilograms to 3.9 kilograms. Many mammals living at the time showed similar reduction in size. But according to the new study appearing in the journal Science, as the climate cooled again some 45,000 years later, the trend reversed, and the mammals including Sifrhippus began to bulk up again. Size variations were done mainly through study of Sifrhippus’s molars, which can give a more accurate determination of size than other bones can. The study points out the effects rapid temperature changes can have on mammalian evolution, and offers further insight into the geologic history of the period.

SOURCES
Story at Physorg.com
Story at Scientific American website