This Ice Age wolf puppy doesn’t look much like a fearsome predator, what with her tiny puppy teeth and soft little ears. According to her DNA, however, the mummified puppy, named Zhùr, came from a population that's among the ancestors of all modern wolves. Canada’s permafrost freeze-dried her remains shortly after her death around 57,000 years ago.
“She’s the most complete wolf mummy that’s ever been found. She’s basically 100 percent intact—all that’s missing are her eyes,” said Des Moines University paleontologist Julie Meachen.
In July 2016, miner Neil Loveless of Favron Enterprises was searching for gold in Canada's famed Klondike gold fields. He was water-blasting the frozen mud along the banks of Last Chance Creek. It’s a process called “hydraulic thawing,” meant to thaw and soften the frozen permafrost so miners can search for gold in the streambed deposits, an approach called placer mining. But Loveless found something far stranger and even more interesting than Klondike gold: a frozen, mummified wolf puppy.
“We thank [Loveless] for his keen eye spotting Zhùr as she was melting out of the permafrost, ensuring she was kept safe in a freezer, and then reporting the discovery to Yukon Paleontology,” wrote Meachen and her colleagues in a recent paper in the journal Current Biology. Studying 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 very closely with the people who have called this region home for thousands of years, like the Tr'ondëk Hwëch'in First Nation.
Members of the group gave the puppy her 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 puppy could teach us about Pleistocene wolves. The First Nation agreed to display the mummy at the Yukon Beringia Interpretive Center in Whitehorse, where she has been cleaned, conserved, and studied.
“We are grateful for the partnership with Tr'ondëk Hwëch'in in our shared role in protecting and preserving heritage resources in the Klondike,” wrote Meachen and her colleagues.
Taking tiny samples from a few of Zhùr’s incredibly well-preserved hair follicles, Meachen and her colleagues radiocarbon dated the frozen puppy and studied the chemical isotopes in her body, which offered clues about what she ate and the climate in which she lived. They also sequenced her 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 figure that out.
Radiocarbon dating could only tell Meachen and her colleagues that the mummy was older than 50,000 years. The puppy’s genome suggested that she’d lived sometime between 75,000 and 56,000 years ago, based on the rate at which wolf DNA collects mutations over time. And the oxygen isotopes in her body suggested that she had lived during the relatively warm period of Marine Isotope Stage 3, when warmer conditions led to smaller ratios of the isotope oxygen-18 in marine sediment cores—and in Zhùr’s body. MIS 3 spanned a period 57,000 to 29,000 years ago.
All of those possible dates overlapped at one point: 57,000 to 56,000 years ago. At the time, sea levels were much lower than today, and a region of dry land called Beringia connected Siberia and Canada. Animals moved freely back and forth between the continents, which is why Pleistocene wolves unearthed across Eurasia and North America are all so closely related. Zhùr’s mitochondrial DNA fit right into that group of closely related animals, or clade, with a common ancestor that lived between 86,000 and 67,500 years ago.
Zhùr and her clade are the ancestors of every wolf in the world (except possibly , which have apparently been doing their own thing for hundreds of thousands of years, according to a study earlier in 2020).
But because mitochondrial DNA gets passed down directly from mother to puppy, Meachen and her colleagues could tell that Zhùr wasn’t a direct ancestor of the wolves that roam the Klondike today. Sometime in the last 56,000 years or so, the Klondike wolf population died out or left the area, and another group of wolves—one less closely related to Zhùr—replaced it. At the moment, there’s not enough data to tell if the newcomers drove off, outcompeted, or just absorbed Zhùr’s relatives, but the puppy’s DNA hints at an interesting story yet to be explored.
Wolves eat fish, too
If Zhùr couldn’t tell Meachen and her colleagues exactly what happened to a whole population of Klondike wolves, she could at least tell quite a bit of her own story. Based on how her bones had developed, the puppy was about 7 weeks old when she died. Since modern wolves in the area usually give birth in early summer, that means Zhùr probably died in July or early August, around the same time Loveless washed her out of the permafrost 57,000 years later.
By then, Zhùr’s mother had probably weaned her pups from milk and started bringing them real food. Modern wolf puppies start eating solid food at around 5 or 6 weeks old. In Zhùr’s case, that seems to have included a lot of fish, according to the amount of the isotope nitrogen-15 in her body. Nitrogen isotopes offer clues about how far up the food chain an animal might have been and whether more of its food came from land or water.
Given all the fish, the puppy’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,” said Meachen. “One thing that surprised us was that she was eating aquatic resources, particularly salmon.”
Modern wolves in the Alaskan interior have been known to chow down on fish, at least in seasons when they’re readily available. And Zhùr’s den wasn’t far from the Klondike River, where Chinook salmon spawn today. The fish swim up the Yukon River to the Klondike, where they would have been a veritable buffet for a mother wolf looking to feed her pups.
How to freeze-dry an Ice Age predator
Obviously things didn’t end well for Zhùr, or we wouldn’t have a ridiculously adorable canid ice mummy to study today. Her burial can offer a few clues about her untimely end and her uncannily good preservation over the intervening millennia. She must have died in just the right conditions and been buried quickly—a rare combination. “The animal has to die in a permafrost location, where the ground is frozen all the time, and they have to get buried very quickly, like any other fossilization process,” said Meachen.
Animals that get killed by predators don’t tend to form perfectly preserved ice mummies, and animals that die from sickness or exposure also don’t tend to get buried quickly enough to freeze and mummify. And isotopic analysis suggests the puppy was well-nourished, so whatever happened, she probably wasn’t sick and definitely wasn’t starving.
Meachen and her colleagues think Zhùr’s den collapsed, killing her instantly and burying the remains in the freezing ground. “We feel a bit better knowing the poor little girl didn’t suffer for too long,” said Meachen.
There’s another question that Zhùr will never be able to answer, however: why was she alone in the den? Wolf mothers usually have four to six puppies at a time, but only Zhùr was buried alongside Last Chance Creek; no sign of her mother or littermates has turned up. “It could be that she was an only pup, or the other wolves weren’t in the den during the collapse,” said Meachen. “Unfortunately, we’ll never know.”
A cautionary tail
Permafrost mummies of large mammals, like mammoths, bears, and even wolves, are rare finds for paleontologists. But smaller ones, like ground squirrels and ferrets, turn up more often in places like Siberia and the Yukon. Meachen and her colleagues speculate that animals who lived in burrows or dens, including wolf pups, may have had better odds of getting preserved in the permafrost, especially if they died in cave-ins.
Even large permafrost mummy finds are getting more common, though. A cave bear emerged from the Siberian permafrost earlier this year, and it’s one of several recent finds. “One small upside of climate change is that we’re going to find more of these mummies as permafrost melts,” said Meachen. “That’s a good way for science to reconstruct that time better, but it also shows us how much our planet is actually warming.”
Current Biology, 2020 DOI: (About DOIs).