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Mammoths and North American horses vanished later than previously thought: researchers

Mammoths didn’t die out until about 6,000 years ago — more recently than previously believed — as did the wild horses that once grazed the plains of North America, according to new findings out of McMaster University.

A team of scientists used permafrost soil to study DNA record of 30,000 years of natural history

An illustration of mammoths and North American horses during the Pleistocene period. The Yukon once resembled an African savannah, says Tyler Murchie, a postdoctoral fellow at McMaster University. (Julius Csotonyi)

Mammoths may not have disappeared until about 6,000 years ago — more recently than previously believed — as did the wild horses that once grazed the plains of North America, according to new findings out of McMaster University. 

A team of scientists in Hamilton as well as the University of Alberta, the Government of Yukon and the American Museum of Natural History, used ancient DNA in soil samples from the Klondike region of central Yukon to study 30,000 years of natural history.

"Just from gathering tiny flecks of dirt — in this case between about 0.5 and 1 gram, which is very little sediment — we can reconstruct the whole ecosystem with a variety of animals that existed in the area," said Tyler Murchie, a postdoctoral fellow at McMaster University and lead author on the paper. 

The team was particularly interested in the Pleistocene-Holocene transition, an unstable period around 11,000–14,000 years ago when large animals such as mammoths, mastodons and sabre-toothed cats disappeared. 

Their paper, published in Nature Communications, found that mammoths and North American horses were in steep decline before the Pleistocene-Holocene period, but didn't disappear 13,000 years ago as bone records suggested. Instead, the DNA evidence shows that they were still around as early as 6,000 years ago. 

That puts the disappearance of mammoths in the Yukon in the current geological epoch, the Holocene, that began about 11,000 years ago. By the time mammoths disappeared from the region, human civilizations were emerging around the world and early cities were developing.

Tyler Murchie, pictured, said new methods of studying ancient DNA could eventually resolve long-standing questions about the role of humans in the disappearance of animals like mammoths and wild Yukon horses. (Georgia Kirkos)

DNA preserves best in permafrost, because it is cold and there is very little degradation from liquid water, oxygen or the sun, Murchie said. Using DNA capture-enrichment technology developed at McMaster, the scientists extracted DNA preserved in the soil to discover when species appeared and disappeared from the region.

"They're just kind of locked in place until someone comes along and is able to recover those fragments," Murchie said.

During the period studied, the Yukon environment transitioned from the rich grasslands known as the "Mammoth Steppe" to the thick boreal forests that exist today. Murchie said that one theory is that as large grazing animals disappeared, they were no longer able to keep plant life in check.

"Part of this theory is that much of the Northern Hemisphere was analogous to the modern African savanna," he said. "But as a lot of these big animals started to disappear, those kinds of ecological networks began to break down." 

Murchie added that it could be early evidence of the impact of humans on ecosystems. Scientists still disagree on whether humans, a warming climate or a combination of the two caused the extinction of large animals like mammoths, he said.

Because ancient DNA preserves best in cold conditions, permafrost in areas like the Yukon is ideal for soil samples. (Tyler Murchie)

He said reconstructing ancient ecosystems could help to get to the bottom of this question and other debates that have raged between scientists "at least 270 years."

Ross MacPhee from the American Museum of Natural History co-authored the study. He said the study provides further evidence that the horse is native to North America.

"Although mammoths are gone forever, horses are not," he said. "The horse that lived in the Yukon 5,000 years ago is directly related to the horse species we have today."

There may be a time limit on the research. Permafrost is thawing quickly in the Arctic as the earth warms, which has created a sense of urgency to collect DNA samples that can reveal the earth's natural history. 

"If we don't collect the samples, and they just thaw and degrade, then we lose all that life history data that's been preserved for all this time," Murchie said.

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