From CBC News: A horse leg bone up to 700,000 years old, found a decade ago in Yukon permafrost near the Alaska border, has supplied scientists with a complete genetic profile of the animal.
The analysis of the ancient genome suggests that it is likely possible to piece together the genomes of organisms that lived as far back as a million years ago, said Ludovic Orlando, the lead author of the paper describing the discovery, at a press briefing organized by the journal Nature in which the paper was published Wednesday. ...
[After] the ancient horse's genome was compared with that of the only living wild horse species, the Przewalski's horse; modern horses; and donkeys, the team learned a lot about horse evolution.
They found that the common ancestor of the species they analyzed arose around four million years ago — twice as early as previously thought. It appears the Prezwaski horse diverged from the modern domestic horse about 50,000 years ago and hasn't mixed with the domestic horse since. Over time, some parts of the genome that showed the biggest changes were the genes that control the ability to smell and the animal's immune system.