Yukon gold miner discovers mummified Ice Age wolf cub

This Ice Age wolf cub doesn’t look much like a fearsome predator, with his tiny puppy teeth and fluffy little ears. However, according to its DNA, the mummified cub, named Zhùr, came from a population that is among the ancestors of all modern wolves. Canada’s permafrost lyophilized his remains shortly after his death about 57,000 years ago.

“It is the most complete wolf mummy ever found. It’s basically 100 percent intact, all it’s missing is its eyes, ”said Julie Meachen, a paleontologist at Des Moines University.

Puppy surprise

In July 2016, miner Neil Loveless of Favron Enterprises was prospecting for gold in Alaska’s famous Klondike gold fields. He was cleaning up the frozen mud along the banks of Last Chance Creek. It’s a process called “hydraulic thawing,” intended to thaw and soften frozen permafrost so that miners can search for gold in riverbed deposits, a method called pleasure mining. But Loveless found something far stranger and even more interesting than Klondike gold: a frozen mummified wolf cub.

“We appreciate [Loveless] because his watchful eye saw Zhùr as he melted from the permafrost, making sure it was kept safe in a freezer and then reporting the discovery to Yukon Paleontology, ”Meachen and colleagues wrote in a recent article in Current Biology magazine. Studying the Pleistocene wildlife in the Yukon means working with gold mining companies, whose workers might be the first to spot something like Zhùr. Scientists like Meachen also work closely with the people who have called this region home for thousands of years, such as the Tr’ondëk Hwëch’in First Nation.

Members of the group gave the cub its name, Zhùr, which means “wolf” in the Hän language. Zhùr is a culturally significant find for the Tr’ondëk Hwëch’in, but they were also interested in how much the frozen cub could teach us about Pleistocene wolves. The First Nation agreed to display the mummy at the Yukon Beringia Interpretation Center in Whitehorse, where it has been cleaned, preserved and studied.

“We are grateful for partnering with Tr’ondëk Hwëch’in in our shared role in protecting and preserving heritage resources in the Klondike,” Meachen and colleagues wrote.

Taking tiny samples from some of Zhùr’s incredibly well-preserved hair follicles, Meachen and her colleagues radiocarbon dated the frozen puppy and studied the chemical isotopes in its body, offering clues about what it ate and the climate it lived in. They also sequenced their mitochondrial DNA, the genetic material passed down directly from mother to offspring.

The ancestors of modern wolves

Zhùr probably lived around 57,000 years ago, but it took three different dating methods to find out.

Radiocarbon dating was only able to tell Meachen and his colleagues that the mummy was over 50,000 years old. The cub’s genome suggested that it had lived sometime between 75,000 and 56,000 years ago, based on the rate at which the wolf’s DNA accumulates mutations over time. And the oxygen isotopes in his body suggested that he had lived during the relatively warm period of Marine Isotope Stage 3, when warmer conditions led to smaller proportions of the oxygen-18 isotope in marine sediment cores and in the body. by Zhùr. MIS 3 spanned a period from 57,000 to 29,000 years ago.

All of those possible dates overlapped at one point: 57,000 to 56,000 years ago. At that time, sea levels were much lower than they are today, and a region of dry land called Beringia connected Siberia and Canada. Animals freely moved back and forth between continents, which is why the Pleistocene wolves unearthed in Eurasia and North America are so closely related. Zhùr’s mitochondrial DNA fits perfectly into that closely related group of animals, or clade, with a common ancestor that lived between 86,000 and 67,500 years ago.

Zhùr and his clade are the ancestors of all the wolves in the world (except possibly the high-altitude Himalayan wolves, which have apparently been doing their thing for hundreds of thousands of years, according to a study conducted in early 2020).

But because mitochondrial DNA is passed directly from mother to cub, Meachen and his colleagues were able to tell that Zhùr was not a direct ancestor of the wolves that roam the Klondike today. At some point in the last 56,000 years or so, the Klondike wolf population became extinct or left the area, and another group of wolves, one less related to Zhùr, replaced it. At the moment, there is not enough data to say whether the newcomers left, outperformed the competition, or simply absorbed Zhùr’s relatives, but the pup’s DNA points to an interesting story that has yet to be explored.

Wolves eat fish too

If Zhùr couldn’t tell Meachen and his colleagues exactly what happened to an entire population of Klondike wolves, he could at least tell a little of his own story. Based on how his bones had developed, the cub was around 7 weeks old when he died. Since modern wolves in the area usually give birth in early summer, that means that Zhùr likely died in July or early August, around the same time that Loveless pulled her out of the permafrost 57,000 years later.

By then, Zhùr’s mother had probably weaned her cubs from milk and started bringing them real food. Modern wolf pups begin to eat solid food around 5-6 weeks of age. In Zhùr’s case, that seems to have included a lot of fish, based on the amount of nitrogen-15 isotope in his body. Nitrogen isotopes offer clues as to how high up the food chain an animal might have been, and whether more of its food comes from land or water.

Considering all the fish, the cub’s breath must have been atrocious. “Normally when you think of wolves in the Ice Age, you think of them eating bison or musk oxen or other large animals on land,” Meachen said. “One thing that surprised us was that it was eating aquatic resources, particularly salmon.”

Modern wolves in the interior of Alaska have been known to devour fish, at least in the seasons when they are available. And Zhùr’s den was not far from the Klondike River, where Chinook salmon spawn today. The fish swim down the Yukon River to the Klondike, where they would have been a veritable buffet for a mother wolf looking to feed her cubs.

How to freeze an Ice Age predator

Obviously, things didn’t end well for Zhùr, or we wouldn’t have a ridiculously lovable canid ice mummy to study today. Its burial may offer some clues to its untimely end and its astonishingly good preservation during the intervening millennia. It must have died in the right conditions and been quickly buried, a rare combination. “The animal has to die in a place of permafrost, where the ground is frozen all the time, and they have to be buried very quickly, like any other fossilization process,” Meachen said.

Animals that are killed by predators do not tend to form perfectly preserved ice mummies, and animals that die from disease or exposure also do not tend to bury themselves fast enough to freeze and mummify. And the isotopic analysis suggests that the pup was well fed, so whatever happens, she was probably not sick and was definitely not starving.

Meachen and his colleagues believe that Zhùr’s lair collapsed, killing her instantly and burying the remains in the frozen ground. “We feel a little better knowing that the poor girl didn’t suffer for long,” Meachen said.

However, there is another question that Zhùr will never be able to answer: why was she alone in the studio? Wolf mothers typically have four to six cubs at a time, but only Zhùr was buried next to Last Chance Creek; no sign of his mother or littermates has appeared. “It could be that she was a single cub, or that the other wolves were not in the den during the collapse,” Meachen said. “Unfortunately, we will never know.”

A wary tail

Permafrost mummies of large mammals, such as mammoths, bears, and even wolves, are rare finds for paleontologists. But the smallest ones, like ground squirrels and ferrets, appear more frequently in places like Siberia and the Yukon. Meachen and her colleagues speculate that animals that lived in burrows or dens, including wolf cubs, may have been more likely to be preserved in permafrost, especially if they died in landslides.

However, even large permafrost mummy finds are becoming more and more common. A cave bear emerged from the Siberian permafrost earlier this year, and it’s one of several recent finds. “One small advantage of climate change is that we are going to find more of these mummies as the permafrost melts,” Meachen said. “That’s a good way for science to better rebuild that time, but it also shows us how much our planet is warming.”

Current Biology, 2020 DOI: 10.1016 / j.cub.2020.11.011 (About DOIs).