Extinct horse species ranged further and survived longer than first thought

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An extinct species of horse ranged thousands of kilometers further east than first thought and died out much later than originally suspected, fresh research has shown.

Scientists in China and Germany used molecular technology to test fossils recovered in China, revealing that the species involved was Equus ovodovi, remains of which had previously been recovered only in Russia.

Jun-Xia Yuan and his colleagues, writing in the open-access journal PLOS ONE, said they retrieved three near-complete mitochondrial genomes from the specimens.

Sussemionus is a recently described subgenus of Equus thought to have originated in Alaska during the Pliocene. Its representatives were widely distributed from North America to Eurasia and Africa.

Although fossil materials of Sussemionus are abundant, its evolutionary history is not yet well understood. It was previously believed that all its members were restricted to the Early and Middle Pleistocene.

However, ancient DNA analyses and fossil evidence from Proskuriakova cave and Denisova cave in Russia verified that at least one species of Sussemionus, E. ovodovi, survived as recently as the Late Pleistocene.

E. ovodovi was a confusing fossil species in terms of its features. The form of the fossils indicated the specimens belonged to the subgenus Sussemionus, subsequently named as a different species, E. ovodovi.

These specimens were dated to the Late Pleistocene according to the stratigraphic layer, which challenged the previous view of Sussemionus having gone extinct around half a million years ago.

Paleontologists went on to identify additional Late Pleistocene E. ovodovi fossils around Russia. Complete mitochondrial genomes were retrieved from two of these Late Pleistocene E. ovodovi specimens.

Until now, none have been identified outside the political boundaries of present-day Russia.

The authors noted that many equid fossils have been found in Pleistocene strata in Northern China.

Paleontologists have carried out detailed studies of their form, identifying E. hemionus, E. przewalskii, and the extinct Equus dalianensis.

Molecular analysis by the current study team revealed the existence of a fourth horse species, E. ovodovi, in northern China.

For their research, the study team extracted DNA from three equid fossil specimens excavated from northeastern China dated at 12,770 to 12,596 years ago, 29,525 to 28,887 years ago, and 40,201 to 38,848 years ago. They had previously been identified, based on their form as E. dalianensis.

The scientists retrieved three near-complete mitochondrial genomes from the specimens, analysis of which showed that these specimens actually clustered with the Russian E. ovodovi.

“The molecular identification of E. ovodovi in northeastern China extends the known geographical range of this fossil species by several thousand kilometers to the east,” they said.

The specimen with the youngest radiocarbon age of about 12,500 years ago is the first E. ovodovi sample dating to the very end of the Pleistocene.

This, they said, moved the extinction of the species forwards considerably compared to previously documented fossils.

The species probably vanished from its Pleistocene habitats when the climate became more humid and warmer than during previous time periods, they suggested.

Comparison of the three mitochondrial genomes with the two published ones suggests a genetic diversity similar to several modern species of the genus Equus.

The full study team comprised Jun-Xia Yuan, Xin-Dong Hou, Axel Barlow, Michaela Preick, Ulrike Taron, Federica Alberti, Nikolas Basler, Tao Deng, Xu-Long Lai, Michael Hofreiter and Gui-Lian Sheng.

Yuan J-X, Hou X-D, Barlow A, Preick M, Taron UH, Alberti F, et al. (2019) Molecular identification of late and terminal Pleistocene Equus ovodovi from northeastern China. PLoS ONE 14(5): e0216883. https://doi.org/10.1371/journal.pone.0216883

The study, published under a Creative Commons License, can be read here

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