57,000 year-old wolf puppy found frozen in Yukon permafrost

The preserved pup is helping researchers understand how wolves migrated across Europe, Asia, and North America.

Published 22 Dec 2020, 12:15 GMT
A well-preserved wolf pup has been recovered from permafrost in the Yukon Territory of northern Canada, ...

A well-preserved wolf pup has been recovered from permafrost in the Yukon Territory of northern Canada, revealing new details about how ancient wolves spread across North America and Eurasia.

Photograph by Government of Yukon

In the summer of 2016, a gold miner in Canada’s Yukon Territory found an unexpected treasure. While blasting a wall of permafrost with a water cannon to release whatever riches might be found inside, Neil Loveless saw something melting out of the ice. It wasn’t a precious mineral, but the oldest and most complete wolf mummy ever discovered.

Loveless quickly placed the frozen pup in a freezer until palaeontologists could have a look. They found that the well-preserved animal was a juvenile female, part of a vanished ecosystem dating to a time when northwestern Canada was home to American mastodons and other Pleistocene megafauna. The local Tr’ondëk Hwëch’in people named the 57,000-year-old pup Zhur, meaning “wolf” in the language of their community.

Exceptional mammals have been recovered from the Siberian tundra that also date back to the Pleistocene epoch, a period from about 2.6 million to 11,700 years ago also sometimes called the Ice Age, because the ice caps at the poles were much larger than today. However, finding such an intact wolf in the Yukon is unprecedented.

Only seven weeks old when she died, the young gray wolf belonged to a population that first arrived in the Yukon region by migrating from Siberia across the Bering land bridge.

Photograph by Government of Yukon

“In Siberia, preservation like this is fairly common because of the way the permafrost preserves things there, which is way less common in the Yukon, Alaska, and other parts of North America,” says Des Moines University palaeontologist Julie Meachen, who is the lead author of a study describing Zhur published today in the journal Current Biology. Much of Zhur has remained intact after tens of thousands of years, from the fur of her coat to the delicate papillae on her tongue.

“The preservation looks amazing,” says University of Copenhagen palaeontologist Ross Barnett, who was not involved with the study. But there’s more to Zhur than what can be seen with the naked eye. “She tells us a lot,” Meachen says, from her age at death—seven weeks—to what she was eating. The research offers a glimpse at a period of respite between icy spans of Earth’s history.

A lost wolf population

Zhur lived during an interglacial, when the vast Arctic glaciers temporarily receded, and woodlands overtook the chillier grasslands. These were the times of mastodons, camels, giant beavers, and, as Zhur documents, grey wolves.

“To have such extraordinary preservation of a carnivore is a unique situation to look into Ice Age ecosystems from a predator’s point of view,” says McMaster University palaeogeneticist Tyler Murchie, who was not involved in the study.

An illustration of a gray wolf hunting fish with it's pup in northwestern Canada nearly 60,000 years ago.

Photograph by Illustration by Julius Csotonyi

While they are iconic parts of the modern North American wilderness, gray wolves did not evolve in the Americas. These canids first appeared in Eurasia and crossed the Bering land bridge late in the Pleistocene epoch, more than 500,000 years ago.

“Zhur is from a time period that isn’t very well-known in the Yukon in terms of mummies,” Barnett says. And by examining the remnants of the wolf pup’s DNA, Meachen and colleagues found that this animal documents a group of wolves that no longer exist in the region.

Zhur belonged to a population of that had genetic connections to wolves in both Alaska and Eurasia, but wolves living in the Yukon today have a different genetic signature. The findings suggest the first grey wolves in the Yukon were wiped out and later replaced by other populations that had already made their way farther south.

The amazing preservation of the wolf pup Zhur allows scientists to study both the animal's physical features and its DNA.

Photograph by Government of Yukon

“Ancient DNA repeatedly demonstrates how much more complex evolutionary histories and palaeoecology are than we might otherwise derive from studies of bones and fossils,” Murchie says. Without Zhur’s genes, this extirpation and replacement would have been invisible to scientists.

A prehistoric life cut short

Zhur’s body also tells us about her life. Only about seven weeks old when she died, the pup had just passed weaning age, when she would have begun eating more solid foods. The geochemical signatures in her teeth indicate that she subsisted on meals from rivers and streams, perhaps fish like the Chinook salmon that still spawn in the rivers near where she was found. Many modern wolves in the interior of Alaska have similar diets, noshing on fish more often than big game.

Sadly, Zhur’s life was cut short. She seems to have died in a den collapse, the rapid burial facilitating the exceptional preservation of her body. Other mammals from this time—such as Arctic ground squirrels and black-footed ferrets—have been preserved in the same way.

Zhur existed at ancient intersections, not just between cold glacial periods, but between populations of wolves that are now separated. By studying the pup’s genes, scientists can gain a greater understanding of her place in the ancient world and what has changed since then. “Ancient DNA is bringing to life the dynamism of the Late Pleistocene that was mostly invisible from just the bones,” Barnett says.

How populations of animals shifted around during the Pleistocene is a story that’s still being teased out from tatters of ancient DNA left in preserved specimens, but Zhur’s remains offer important clues. Where bones and genes meet, researchers are getting a new window into the lost worlds of the Ice Age.

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