A lost species of yak, hiding in Denisova Cave's bone pile

Denisova Cave holds a mountain of bone fragments so smashed that 95% can't be identified by eye. Reading their DNA, geneticists found at least 20 genomes of a previously unknown bovine — 'yak X' — a sister species to the modern Himalayan yak that split off some 400,000 years ago. The animal that once roamed outside the cave may even have been on the menu of Denisovans and Neanderthals.