Bones tell a horse story from the Yukon steppes

Early this summer, the Dawson gold fields broke into international news yet again. This time, 115 years after the original Klondike stampede, it was bones, not gold, that drew the world's attention to Canada's far northwest.

by Erling Friis-Baastad

Early this summer, the Dawson gold fields broke into international news yet again. This time, 115 years after the original Klondike stampede, it was bones, not gold, that drew the world’s attention to Canada’s far northwest. A team of scientists revealed, in the June 26 issue of the journal Nature, that sequencing DNA from a foot bone of a mid-Pleistocene Yukon horse had allowed them to look back in time 700,000 years.

From that grand perspective they could make new, more accurate deductions about Pleistocene Arctic megafauna in general, and the development of modern horses in particular. It’s a multi-faceted story, involving, among other individuals and institutions, the universities of Alberta, California at Santa Cruz, and Copenhagen, the Yukon’s paleontology branch and Dawson-area gold miners.

The story’s significance varies depending on the observer’s primary area of interest. The sequencing of a fragment of DNA of such great age promises to open ever-wider windows onto the process of mammalian evolution, the Far North’s contribution to species development, the development of horses specifically and even conservation priorities.

Duane Froese, a professor at the University of Alberta in Edmonton and co-discoverer of horse bones at Nancy and Stuart Schmidt’s placer mine in Thistle Creek, is particularly enthralled by large Pleistocene steppe grazers. In fact, 7,000 centuries ago is a significant moment in the process of the development of ice-age megafauna, Froese says. “This is the time when we see the development of steppe fauna, the development of horse and mammoth.”

“One of the really neat aspects of what we learn from genetics back that far is that the caballid line of horses, the ones that are ancestral to modern horses – that ultimately get domesticated – were roaming around the Yukon 700,000 years ago,” he says.

“Probably a lot of their evolution took place in the Arctic.”

In order to understand the significance of the Thistle Creek finds, it’s important to cast off some popular misconceptions – especially the one that claims the horse started out as a dog-sized Eohippus some 50 million years ago and then centimetre by centimetre reached the stature of today’s horses. “It turns out it’s a lot more complicated than that when we actually start looking at the fossil record,” says Froese. There have been many species of horses over thousands of millennia, even within the Pleistocene. The very old specimen found at Thistle Creek stood out because it was so much larger than the horses that roamed the area a mere 30,000 years ago.

Froese has been exploring the gold fields since he was an undergraduate working with the Canadian Geological Survey in the mid-1990s. The treasures within the muck and permafrost near Dawson called him back repeatedly throughout his graduate studies, his post-doctoral work and professorship. It was the Schmidts who originally brought horse bones to the attention of the scientist. “I had originally vetted the site prior to that but had not found any of the fossils,” he says.

Encouraged by the Schmidts, he returned to the site which they had continued to work, revealing new permafrost and new bones. Froese recognized the 2003 find “right away as a larger horse. Yes, they jump out at you. They’re probably 20 to 30 per cent larger than most of the horses that we find.”

However, most of the megafauna fossils from the Yukon Pleistocene date only to 30 to 40 thousand years ago, says Froese. Sites of 7,000 centuries ago are very, very rare. And the scientists were especially lucky because that site had significant permafrost to preserve the bones and DNA. It’s called relict permafrost, says Froese, because it hasn’t thawed since it was formed. The icing on that particular paleontological cake was a previously-dated layer of ash that lay just above the ice where the bones were found.

Other bones, also found at that level, helped prove that horses shared the dry, cold grasslands with woolly mammoths. Steppe bison showed up in North America much later, and proved more adaptable to the increased shrub cover and diminished grasslands of the late Pleistocene. Perhaps one of the reasons why the 700,000-year-old horse was so much larger than the horses of the late Pleistocene was that the earlier ones didn’t have to compete with steppe bison. “It’s only a speculation at this point, but an interesting one,” says Froese.

Horses likely shared the landscape with giant beaver, peccaries, sheep and caribou. But it’s anyone’s guess if the first human Yukoners ever saw horses. It’s possible, though the horses were approaching extinction as the Holocene came on, Froese says.

Archeologists have determined that humans settled at Scottie Creek in the Tanana River drainage, near what is now Beaver Creek, by at least 11,200 years ago. Some scientists suggest that human hunters brought about the end of the horses, but Froese doesn’t hold with that theory. The horses had already shrunk in size and were on their way out when humans showed up, he says. Besides, if hunters were such a factor in the disappearance of horses, why did populations of moose and elk expand at that time?

At any rate, by the time the Holocene epoch began about 10,000 years ago, the North American horse was extinct. Prior to that, horses would have travelled both ways over the Beringia land bridge, and their relatives back in Siberia have survived. Equus cabellus wouldn’t gallop across the North American wilds again until reintroduced by Spanish soldiers in the 16th century.

No paleontologist ever speaks about the rich fossil heritage of the Klondike gold fields without praising placer miners. Froese is no exception. “This has been one of the great things about going back there year after year, as miners get to know what you’re interested in and what you’re doing,” he says. “They’re a tremendous resource.”

“I am very excited about this find for sure,” Nancy Schmidt wrote in an email to Your Yukon. “This is especially exciting to Stuart and me because we love horses and have 10 of our own. It is also an important example of what the Yukon placer mining community can offer the rest of the world.”

This column is co-ordinated by the Yukon Research Centre at Yukon College with major financial support from Environment Yukon and Yukon College. The articles are archived at www.yukoncollege.yk.ca/research/publications/newsletters/_articles

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