Swedish-Led Team Identifies Unknown Extinct Yak Species in Siberia's Denisova Cave

Scientists have identified a previously unrecorded extinct bovine species closely related to modern yaks, based on ancient DNA extracted from bone fragments found in Denisova Cave and other sites across the Altai-Sayan Mountains in southern Siberia. The findings were published in the journal Current Biology on October 5, 2026.

The research team, based at the Centre for Palaeogenetics — a joint institute of Stockholm University and the Swedish Museum of Natural History — worked with colleagues from the University of California, Santa Cruz, and the University of Vienna. The study's senior author is Love Dalén, Professor of Evolutionary Genomics at the Centre for Palaeogenetics, with Alexandre Gilardet and Jonas Oppenheimer listed among the researchers who carried out the genomic analysis.

How an unnamed species was found in tiny bone fragments

The bones used in the study were too small and too fragmented to be identified by their shape alone, according to the researchers. Instead, the team sequenced ancient DNA from the fragments and reconstructed 20 nuclear genomes spanning more than 200,000 years, from roughly 247,000 to about 27,000 years old. Comparing this genetic material to known bovine species — including modern yaks, steppe bison and aurochs — revealed a distinct, previously undescribed lineage that the team has informally nicknamed "yak X."

Because the species has not yet been compared against all previously described regional bovine fossils, it has not received a formal scientific name. The researchers say further work is needed before yak X can be classified under a Latin binomial.

A separate lineage for hundreds of thousands of years

According to the genomic analysis, yak X began diverging from the ancestors of today's yaks at least 400,000 years ago and had become a fully separate species by around 250,000 years ago. The data also point to a population replacement within the yak X lineage roughly 120,000 years ago, a period researcher Alexandre Gilardet noted overlaps with a particularly strong warm climatic phase.

The youngest bone fragment in the dataset is about 27,000 years old, meaning yak X was still present in the region well into the last Ice Age. The exact timing and cause of its extinction remain unknown, since no younger specimens have been found so far.

Little sign of mixing with other bovines

Unlike the well-documented interbreeding among ancient human groups such as Denisovans, Neanderthals and modern humans — whose remains have also been recovered from Denisova Cave — the genomic data show little to no evidence that yak X interbred with other bovine species living in the same region, such as steppe bison or aurochs, the researchers reported.

Postdoctoral researcher Jonas Oppenheimer noted that the long time span covered by the dataset, more than 200,000 years from a single set of sites, is unusually rare in ancient DNA research. The team also raised the possibility that ancient humans who inhabited the Altai region, including Denisovans and Neanderthals, may have hunted yak X, though the study does not present direct evidence of this beyond the shared presence of their remains at the same sites.

Why the Altai region matters

Dalén said the discovery highlights the Altai-Sayan region as a possible biodiversity hotspot and refugium that preserved distinct animal lineages across repeated glacial cycles during the Pleistocene. Denisova Cave itself is already known among paleoanthropologists as the site where Denisovans, an extinct group of archaic humans, were first identified through ancient DNA.

The study is based on specimens collected from Denisova Cave and additional nearby sites in mid-latitude Asia, and the authors say the approach — recovering genomic information from bone fragments that cannot be identified visually — could help uncover other unknown extinct species hidden in museum and excavation collections from the same period.