Exciting horse fossil discovery in Nevada desert

May 22, 2013; 09:30 AM
San Bernardino County Museum scientists excavating an Ice Age mammoth skeleton from the Tule Springs area north of Las Vegas have found a skull and lower jaw of an ancient horse never before reported at the site or in Nevada.

Horses are not uncommon in the Tule Springs fossil record, but not Equus scotti, a large horse common in much of western North America during the Pleistocene Epoch, or Ice Age.

Las Vegas-area volunteers were instrumental in the discovery.

“Our research funding from the Bureau of Land Management includes a strong public outreach component,” said Kathleen Springer, the museum’s senior curator of geological sciences and lead scientist for the research program in the upper Las Vegas Wash. “Because of this, we set up Nevada’s first paleontology-based site stewardship program, getting local citizens involved in our research. And now it’s paid off — in a big way.”

Springer discovered the fossil site in 2003, during survey conducted by museum scientists and funded by the Las Vegas district office of the Bureau of Land Management. The original find — a tusk and tooth of a mammoth just peeking out at the surface — suggested that multiple parts of the skeleton might be present.

In 2012, Springer’s mammoth site was selected for excavation as part of the BLM’s celebration of 50 years of science at Tule Springs. The presence of multiple bones made it ideal for excavation by site stewards working with museum paleontologists.

Brushing through desert sediments at the surface quickly revealed fragments of horse teeth mixed in with the mammoth fossils. Careful digging teased out more horse teeth, then both sides of the lower jaw, and finally, the skull.

The new finds preserve anatomical features never before seen in any horses from Tule Springs, making firm identifications possible for the first time. The site is nearly 12,000 years old, making the fossils among the youngest records of Equus scotti anywhere in North America.

The discovery is forcing scientists to revise their understanding of horse evolution and extinction at the end of the Ice Ages.

Horse fossils are fairly abundant from Tule Springs and the upper Las Vegas Wash, said Eric Scott, the museum’s curator of paleontology. His studies have revealed that three species of horse lived in the area during the Pleistocene Epoch.

But none of the earlier remains discovered there were sufficiently complete to make firm species identifications possible.

“There have been some species names suggested here and there, but nothing really concrete,” Scott said. “It’s a long-running joke with our team in Vegas that every time a new site is excavated, I plead for them to find a horse I can name.”

With identifiable horse fossils so scarce, paleontologists have had to make inferences about what horse species were present around Tule Springs. Other scientists proposed that the large horse found at the Rancho La Brea tar pits in Southern California also lived throughout the Mojave Desert and the Southwest.

“We now think that’s erroneous,” Scott said. “Our new horse from Vegas has a different anatomy from the big La Brea horse. It looks more like large Ice Age horses from northern Nevada that were living at about the same time.”

The new discovery shows that Equus scotti survived in southern Nevada until the end of the Pleistocene, which was not previously known. In Southern California, the species was replaced in the later Ice Ages by an anatomically distinct form.

“That’s likely either a pulse of evolution — a speciation event — or else the immigration of a different species northwards into California from Mexico,” Scott said. “Either way, we can now clarify the timing and geographic extent of this episode, and the relationships of these two species, in a very exciting way. And it means we had as many as four horse species living in the American southwest at the end of the Ice Ages. Compared to horses today, that’s quite a lot of species.”

Springer said the find emphasizes that “even after decades of work there’s still a lot for us to learn about the Ice Ages at Tule Springs.”

The fossils are under study at the San Bernardino County Museum.

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