Five Fascinating Ice Age Finds Discovered in Yukon Permafrost

In Canada’s Yukon territory, towering pine and spruce forests drape over rolling hills and the Yukon River and its winding tributaries cut valleys into the landscape. Winters in this northwest corner of Canada are harsh, but the warm summer months are illuminated by sunshine until midnight.

Even further north, however, rests the treeless alpine tundra where frigid temperatures permanently keep the ground frozen. The icy soil is called permafrost. For the most part, only moss, lichen and shallow-rooted shrubs can grow in the tundra.

Though moose outnumber people by almost twofold, the Yukon has a bustling mining industry and 14 First Nations groups have thrived on the land for thousands of years. They are descended from the last waves of ancient people who journeyed over the Bering Land Bridge from what is now Siberia at least 15,000 years ago—before the crossing flooded at the end of the last glacial period.

Commonly known as the last Ice Age, the last glacial period began about 100,000 years ago. During this time, most of North America was covered in glaciers, but conditions in what’s now the Yukon were too dry for glaciers to form. Because most of the world’s water was locked up in ice, sea level is estimated to have been as much as 500 feet lower than it is today. This revealed the floor of the Bering Sea, creating a passage between Alaska and Siberia known as Beringia.

Ancient animals made the journey tens of thousands of years before humans, and the Yukon became a vibrant home for giant creatures known as megafauna. Wooly mammoths migrated to North America from Europe and Asia, and generations of Ice Age horses originating in North America may have crossed the land bridge more than once. Giant ancestors of camels, sloths, lions, hyenas and many others populated the landscape. When these animals died, their bodies likely decomposed, and anything that wasn’t scavenged became part of the frozen ground.

Permafrost’s cool touch perfectly preserves nearly anything within it, including DNA. Ancient genes can be easily extracted from bones and soft tissue, and scientists have even found intact genetic material in soil samples.

Today, scientists know how these animals lived and died because their bones and bodies are so well-preserved in permafrost. First Nations people have deep historic knowledge of Ice Age animals as well as their fossils. Likewise, since the Klondike Gold Rush at the turn of the 20th century, miners have uncovered many gargantuan bones—Ice Age relics that continue to be found en masse at mines and river banks today. As climate change advances, permafrost is also thawing rapidly and releasing its contents—a gold rush of sorts for paleontologists.

Here are five fascinating finds that paint a picture of the Yukon’s past.

Near-Perfectly Preserved Wolf Pup

Scientific name: Canis lupus

What makes this find remarkable: "She's the most complete wolf mummy that's ever been found. She's basically 100% intact—all that's missing are her eyes,” study coauthor Julie Meachen, a paleontologist at Des Moines University in Iowa, said in a press release.

What scientists have learned: In 2016, a gold miner blasting a hydraulic water cannon at frozen mud discovered an object paleontologists recognized as a treasure. He’d unearthed a near-perfectly preserved female gray wolf pup that died 57,000 years ago. The Ice Age animal was found on the ancestral land of the Tr'ondëk Hwëch'in people, who named her Zhùr, which means wolf in Hän.

X-rays of her bones and teeth showed she was just under seven weeks old when she died, according to a study published in Current Biology. Scientists ruled out starvation or predator attack as causes of death because she was so pristinely preserved. Instead, they concluded that a den collapse likely killed Zhùr.

Zhùr: A Wolf Pup Mummy from the Yukon / Curr. Biol., Dec. 21, 2020 (Vol. 30, Issue 24)

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Further analysis shows her diet was fish-heavy, which suggests she may have hunted with her mother along rivers as modern wolves do today. Genetic data suggests Zhùr had distant relatives in Eurasia and Alaska. However, wolves living in the Yukon today have a different genetic signature, which means Zhùr’s population was eventually wiped out and replaced by another.

While burrowing animals from this era like arctic ground squirrels and black-footed ferrets have also been found in similar condition, “Mummified remains of ancient animals in North America are incredibly rare,” says Zazula in a statement. “Studying this complete wolf pup allows us to reconstruct how this wolf lived during the Ice Age in ways that would not be possible by looking at fossil bones alone.”

Zhùr is on display at the Yukon Beringia Interpretive Center in Whitehorse.

Western Camel Bones

Scientific name: Camelops hesternus

What makes this find remarkable: The bones rearranged the Camelidae family tree by providing concrete evidence that the animals were closely related to modern camels instead of llamas, according to a 2015 study published in Molecular Biology and Evolution.

What scientists have learned: The camel family, Camelidae, actually originated in North America more than 40 million years ago. Their lineage eventually split into camels and llamas. Ancestors of the dromedary and Bactrian varieties familiar today migrated across the Bering Land Bridge, while predecessors of llamas and alpacas moved to South America.

Meanwhile, now-extinct western camels (Camelops hesternus, which translates to “yesterday’s camels” in Latin) stayed in North America until the end of the Ice Age. While most of them ventured south, even as far as Honduras, some made their way north to Alaska and the Yukon.

For many decades, scientists hypothesized Arctic-dwelling camels were more closely related to llamas and alpacas native to South America because C. hesternus bones resembled a “giant llama” or “llamas on steroids,” says paleontologist Grant Zazula, who works for the Yukon territory.

In 2008, gold miners in Hunker Creek, which is about 60 miles away from the Alaskan border, collected a pile of Ice Age-era bones that date back 75,000–125,000 years. A few peculiar specimens turned out to be several leg bones belonging to an extinct camel species whose remains are rarely found that far North. The bones were so well-preserved in the cold conditions that researchers were later able to extract DNA.

The genetic data showed Ice Age western camels split off from modern-day camels around ten million years ago. Ancestors of today’s camels migrated across Beringia about seven million years ago. The Arctic’s western camels likely traveled north from their typical range during a warmer period about 100,000 years ago before going extinct about 10,000 years ago.

Arctic Hyena Teeth

Scientific name: Chasmaporthetes

What makes this find remarkable: "[There have] been over 50,000 bones of ice-age animals found in the Old Crow area in the past, and we only have two bones or two teeth of this hyena," Zazula told the CBC in 2019. "So it's a very rare animal. It was almost like a needle in a haystack."

What scientists have learned: When most people think of hyenas, they likely picture the stout and scrappy scavengers living in African savannas or arid parts of India. The ancestors of the cackling creatures likely resembled today’s hyenas but had tall, powerful legs for running fast. Chasmaporthetes actually evolved in what is now Europe or Asia more than 5 million years ago, and their remains have been unearthed all over the world, including in Mongolia, Kansas, Mexico—and now, the Yukon.

A fossilized pair of teeth stored in the Canadian Museum of Nature in Ottawa were suspected to be evidence of hyenas living in the ancient Arctic, but a formal analysis wasn’t completed until 2019.

When evolutionary biologist Jack Tseng, who specializes in prehistoric carnivores, finally got to study the teeth in person, he knew “within five minutes” that the molar and premolar indeed belonged to Chasmaporthetes.

Scientists first found the fossilized teeth that now reside at the museum in the 1970s near Old Crow. Charlie Thomas, an elder of the Gwich’in First Nations community, was part of the group to discover them.

Because they were found in a riverbed and not in their original resting place, the teeth are difficult to date. However, based on geology of the basin, researchers estimate the teeth belonged to a hyena that prowled between 850,000 and 1.4 million years ago.

Like today’s hyenas, the ancient arctic beast had a mouthful of chompers perfectly suited for crushing the bones of its prey, which were probably ancient caribou, young bison or maybe even baby mammoths. As for why they went extinct, researchers suspect other Ice Age predators, like the short-faced bear or extinct bone-cracking dog, may have outcompeted Chasmaporthetes for food.

Giant Beaver Skull

Scientific name: Castoroides ohioensis

What makes this find remarkable: “I think any time anyone sees our giant beaver skull, they’re like, ‘Wow, it must have been a sabre-tooth cat and eating people,’” Zazula told Yukon News in 2019.

“No, just pond weeds. It’s almost like, kind of anti-climatic, you know? You have this animal that’s seven feet tall that just eats little pond weeds and you want it to be more dramatic than that, but it’s not.”

What scientists have learned: With a pair of six-inch incisors jutting from its head, the Ice Age giant beaver looked like a fierce predator—but in reality, one of natural history’s largest rodents enjoyed diving for aquatic plants.

At 6 feet long and 220 pounds, Castoroides ohioensis was about the size of a modern black bear. The tail on this massive rodent resembled that of a muskrat more than today’s paddle-tailed Castor canadensis.

But giant beavers weren’t exactly tree-gnawing, dam-building ecosystem engineers like beavers in the Arctic are now. In a 2019 Scientific Reports study, researchers analyzed the chemical signatures in several fossilized bones and teeth found in the Yukon and Ohio estimated to date back between 10,000 and 50,000 years. These tests showed the prehistoric creature preferred aquatic plants.

“Basically, the isotopic signature of the food you eat becomes incorporated into your tissues,” study author Tessa Plint of Heriot-Watt University explained in a 2019 statement. “Because the isotopic ratios remain stable even after the death of the organism, we can look at the isotopic signature of fossil material and extract information about what that animal was eating, even if that animal lived and died tens of thousands of years ago.”

Researchers study the diets of extinct Ice Age megafauna to understand climate change today. These animals thrived in wetter climates and died out 10,000 years ago when it became warmer and drier. They may have been outcompeted by smaller beavers, which also lived during the Ice Age and survived to gnaw on wood today

“It provides a really cool analogue about what’s happening today in the North, because we see animals moving north, north, north all the time now because of warming conditions,” Zazula said to Yukon News.

”…[This migration] happened 100,000 years ago as well,” he continued. “These animals saw these environments moving northward and they followed the environment and ended up in a place where they probably shouldn’t be, like the Yukon, because they’re animals that evolved in more southern conditions.”

Scimitar Cat Bone

Scientific name: Homotherium latidens

What makes this find remarkable: Because relatively few scimitar cat fossils have been found, scientists theorized that only a smaller population of these fanged felines existed, per CBC. This humerus made them reassess.

What scientists have learned: In 2011, a bone was found in permafrost on a Dominion Creek mining site near Dawson City. It belonged to a scimitar cat (Homotherium latidens)—not to be confused with a saber-toothed cat (Smilodon). Scimitar cats have shorter, dagger-shaped canines with serrated edges, unlike their famed relatives, whose teeth typically measured a frightening seven inches long.

However, since the bone was so well-preserved in icy permafrost, researchers at the University of Copenhagen were able to sequence its entire genome. They found that the specimen’s parents were only distantly related, which means the population was large enough to be genetically diverse—more than modern cat species like African lions and lynx, according to a comparative analysis.

Because so much is known about modern human and animal genetics, researchers can identify certain physical details associated with specific genes and then infer how the ancient creature may have behaved, said study author Thomas Gilbert, an evolutionary genomicist at the University of Copenhagen, in a statement.

“Their genetic makeup hints towards scimitar-toothed cats being highly skilled hunters. They likely had very good daytime vision and displayed complex social behaviors,” said Michael Westbury, an evolutionary genomicist at the University of Copenhagen, in a 2020 statement.

“They had genetic adaptations for strong bones and cardiovascular and respiratory systems, meaning they were well suited for endurance running,” he continued. “Based on this, we think they hunted in a pack until their prey reached exhaustion with an endurance-based hunting-style during the daylight hours.”

Because the bone could not be dated using conventional radio-carbon dating, which can only be used to deduce object ages within a certain range, it’s estimated to be more than 47,500 years old. It likely went extinct around 10,000 years ago when other Ice Age animals, including its preferred prey, also died out. "So you have like the woolly mammoth, woolly rhinos, large North American horses, they all went extinct at the same time," Westbury told CBC.

“This was an extremely successful family of cats. They were present on five continents and roamed the Earth for millions of years before going extinct,” says Ross Barnett of the University of Copenhagen in a 2020 statement. “The current geological period is the first time in 40 million years that Earth has lacked saber-tooth predators. We just missed them.”

Rachael Lallensack | READ MORE

Rachael Lallensack is the former assistant web editor for science and innovation at Smithsonian.