Researchers have identified a previously unknown species of extinct bovine, provisionally named yak X, from ancient DNA preserved in bone fragments recovered from Denisova cave in the Altai mountains of Siberia. The species appears to have diverged from the wild yak around 400,000 years ago, became genetically isolated by about 250,000 years ago, and disappeared roughly 30,000 years ago.
«It's not every day that one discovers a previously unknown extinct megafaunal species,» says Love Dalén of Stockholm University, who led the research. The findings, published in Current Biology, add a new branch to the bovine family tree and suggest that early humans in the region encountered an animal unlike any living relative.
The discovery emerged from an effort to study bison evolution. Dalén and his colleagues, including Alexandre Gilardet and Jonas Oppenheimer, examined hundreds of tiny bone fragments from Denisova cave and three other nearby sites, plus one near the Ural mountains. Instead of matching known bison or aurochs DNA, nearly all the fragments carried genetic material from an unrecognized bovine. The team ultimately reconstructed genomes from 20 individuals.
Denisova cave is best known as the site where the Denisovans, an archaic human group, were first identified from a finger bone. The new bovine species would have shared the landscape with Denisovans, Neanderthals and modern humans over its more than 200,000-year existence. «Our results show that yak X was present in the region for more than 200,000 years, and they will likely have had first-hand experience of Denisovans, Neanderthals and modern humans coming and going,» Dalén says.
There is no direct evidence yet that these human species hunted yak X, but Dalén considers it likely that Denisovans, Neanderthals, modern humans and large carnivores such as hyenas and lions targeted the animal as prey. The bones recovered so far all come from much lower elevations than the Tibetan Plateau, the native range of modern yaks, suggesting yak X may have been less adapted to extreme mountain environments.
The genetic distance between yak X and the wild yak is comparable to that between polar bears and brown bears, Dalén notes, indicating the extinct species was ecologically and physically distinct. Until further work is completed, including on remains that may have been previously misidentified, the team cannot say what unique traits yak X possessed. Dalén suspects the species may correspond to yak-like remains that Russian palaeontologists had earlier described as a subspecies of the Himalayan yak.
The research highlights how ancient DNA can reveal hidden chapters of megafaunal history, even from fragmentary bones that had sat unexamined in collections. The team's genomic reconstructions provide a foundation for future studies that may clarify yak X's appearance, behavior and eventual extinction.