A study led by University of Adelaide researcher Julien Soubrier has revealed that prehistoric European cave artists recorded a previously unknown hybrid species of bison and cattle on cave walls more than 15,000 years ago.

The mysterious species originated over 120,000 years ago through the hybridization of the aurochs (Bos primigenius) — an extinct species of ox that inhabited Europe, Asia and North Africa — and the extinct steppe bison (Bison priscus), according to Dr. Soubrier and co-authors.

The study has revealed that the hybrid species eventually became the ancestor of the extant European bison (Bison bonasus).

“Finding that a hybridization event led to a completely new species was a real surprise – as this isn’t really meant to happen in mammals,” said study co-author Prof. Alan Cooper, Director of the Australian Centre for Ancient DNA at the University of Adelaide.

“The genetic signals from the ancient bison bones were very odd, but we weren’t quite sure a species really existed – so we referred to it as the Higgs Bison.”

The team studied genetic material extracted from radiocarbon-dated bison bones and teeth found in caves across Europe, the Urals, and the Caucasus to trace the genetic history of the populations.

The researchers found a distinctive genetic signal from many fossil bison bones, which was quite different from the European bison or any other known species.

Radiocarbon dating showed that the hybrid species dominated the European record for thousands of years at several points, but alternated over time with the steppe bison, which had previously been considered the only bison species present in Late Ice Age Europe.

“The dated bones revealed that our new species and the steppe bison swapped dominance in Europe several times, in concert with major environmental changes caused by climate change,” Dr. Soubrier said.

“When we asked, French cave researchers told us that there were indeed two distinct forms of bison art in Ice Age caves, and it turns out their ages match those of the different species. We’d never have guessed the cave artists had helpfully painted pictures of both species for us.”

The cave paintings depict bison with either long horns and large forequarters — more like the American bison (Bison bison), which is descended from the steppe bison — or with shorter horns and small humps, more similar to the European bison, also known as wisent.

“Once formed, the new hybrid species seems to have successfully carved out a niche on the landscape, and kept to itself genetically,” Prof. Cooper said.

“It dominated during colder tundra-like periods, without warm summers, and was the largest European species to survive the megafaunal extinctions.”

“However, the modern European bison looks genetically quite different as it went through a genetic bottleneck of only 12 individuals in the 1920s, when it almost became extinct. That’s why the ancient form looked so much like a new species.”

The research appears today in the journal Nature Communications.

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Julien Soubrier et al. 2016. Early cave art and ancient DNA record the origin of European bison. Nature Communications 7, article number: 13158; doi: 10.1038/ncomms13158

This article is based on a press-release from the University of Adelaide.