EXCERPT

"We knew that sequencing ancient genomes as old as 70,000 to 80,000 years old was possible," said Ludovic Orlando, an evolutionary geneticist with the Natural History Museum of Denmark at the University of Copenhagen. "So we said, why not try even further back in time?"

The Pleistocene horse genome Orlando and colleagues pieced together helped them determine that the ancestor to the Equus lineage – the group that gave rise to modern horses, zebras, and donkeys – arose 4 to 4.5 million years ago, or about two million years earlier than previously thought.

SOURCE

http://news.nationalgeographic.com/news/2013/06/130626-ancient-dna-oldest-sequenced-horse-paleontology-science/