DNA Horse Fossils Found in North America

A new study of ancient DNA from Horse fossils found in North America and Eurasia shows that horse populations on the two continents remained connected through the Bering Land Bridge, moving back and forth and interbreeding many times over hundreds of thousands of years. The study has been published in the journal Molecular Ecology.

Beth Shapiro, a corresponding author and professor of ecology and evolutionary biology at UC Santa Cruz and a Howard Hughes Medical Institute investigator said that the results of this paper show that DNA flowed readily between Asia and North America during the ice age. It maintains physical and evolutionary connectivity between Horse populations across the Northern Hemisphere.

The study shows the significance of the Bering Land Bridge as an ecological corridor for the movement of large animals between the continents during the Pleistocene when massive ice sheets formed during glacial periods. The lower sea levels uncovered a vast land area known as Beringia, extending from the Lena River in Russia to the MacKenzie River in Canada, with extensive grasslands supporting populations of Horse, mammoths, bison, and other Pleistocene fauna.

Palaeontologists have long known that evolved and diversified in North America. One lineage of horses, known as the caballine Horse dispersed into Eurasia over the Bering Land Bridge about 1 million years ago, and the Eurasian population then began to diverge genetically from the Horse that remained in North America. The new study shows that after the split, there were two periods when moved back and forth between the continents and interbred so that the genomes of North American Horse acquired segments of Eurasian DNA and vice versa.