Frozen squirrel scat preserves ancient DNA from hundreds of species

Frozen squirrel – DNA preserved in frozen coprolites from 13 Arctic ground squirrel burrows in Yukon has helped researchers reconstruct parts of an ice-age ecosystem stretching back 700,000 years, revealing microbes, more than 200 plant groups, and animals ranging from woolly m

By the time the Arctic ground squirrels start waking up again, the work begins fast. They hibernate for about eight months of the year. In the four months they’re conscious. they have to get out. eat. and haul back as many resources as they can to their burrow—turning the space beneath the tundra into a kind of living storage room.

That routine is exactly what makes their frozen droppings so valuable. In central Yukon. in burrows dug by Arctic ground squirrels (Urocitellus parryii). researchers found ancient faecal pellets—coprolites—frozen in permafrost. The burrows dated to between about 30,000 and 700,000 years ago. When the team extracted DNA from those pellets. the results pointed to an ecosystem far richer than what most people would expect from an animal often described as living on nuts and seeds.

The squirrels were collecting from a wide web of life. The DNA included microbes. more than 200 different plant groups. and animals such as insects. other rodents. woolly mammoths. horses. grey wolves. steppe bison. and a big cat that was either an American cheetah or a cougar. “It’s the whole cast of organisms that lived in the Beringian ice-age ecosystem. ” Tyler Murchie of the Hakai Institute in Campbell River. Canada. said.

Beringia—the vast region shaped by past land connections between North America and Siberia—is the backdrop for the story these coprolites are telling. The researchers describe an ecological network reaching back hundreds of thousands of years. when the region included species like woolly mammoths. bison. horses. and big cats.

It would be easy to assume the squirrels mainly carried plant matter back to their burrow. But Murchie says that’s not how it works. “They’re actually quite omnivorous, almost like little bears,” he said. There are reports of ground squirrels eating carcasses of moose and lynx. so finding DNA from large animals inside their coprolites isn’t as surprising as it might sound at first.

Using the DNA they recovered, Murchie and colleagues reconstructed mitochondrial genomes from many animals across different points in time. Their work included 12 ground squirrels, including one lineage dating back 700,000 years, along with three horses, two bison, and one hare. They also found enough DNA to piece together six woolly mammoth genomes. with the details of those mammoth results planned for publication separately.

Kelsey Witt of Clemson University in South Carolina called the samples “fantastically preserved,” adding that they “really showcase the ecological diversity of the Yukon through time.”

Still, there’s a hard problem researchers can’t wish away. Witt said it can be difficult to know whether DNA from a given species appears in a coprolite because the animal was eaten by a ground squirrel. or because it existed in the environment and leached into the material. But she also said it is feasible that the rodents consumed mammoth meat. given how much DNA was present in the samples and the fact that ground squirrels are often scavengers.

In the end, the study turns a small, ordinary creature into an unlikely timekeeper. Burrows and pellets—things most people would never think of as archives—are now carrying molecular fingerprints from a Beringian world that ended long before today’s Arctic ground squirrels ever woke up.

ancient DNA coprolites Arctic ground squirrel permafrost Beringia woolly mammoth genomes mitochondrial genomes paleoecology Yukon