In the long quest to understand what life was like for the saber-toothed cats, bison, and mammoths that roamed North America’s dry tundra during the last Ice Age, scientists have hit on a potent new tool: ancient poop. Specifically, the new tool is ancient DNA, miraculously preserved for up to 700,000 years in ground squirrel scat.

“It’s a whole new source of genomic information,” says Tyler Murchie, a paleoecologist and geneticist at the Hakai Institute, a nonprofit research organization in British Columbia. 

Roughly 12,000 years ago, the planet’s climate shifted abruptly. In the span of about 10,000 years, the towering ice sheets that had dominated much of North America for the previous 2.6 million years disappeared. As the Pleistocene epoch came to an end, the ecosystem in what is now northern Canada transformed from a vast dry tundra dominated by massive mammals to the boggy, forested landscapes of the Holocene—our current epoch—and its abundance of smaller grazers and less prominently fanged predators.

Tracing the ecological consequences of this cataclysm has relied, to date, on analyzing the fragmentary bits of ancient DNA that persist in lake sediments or fossils. In the early 2000s, however, researchers stumbled on another source of millennia-old genetic material that was all but hiding in plain sight. Yukon gold miners have long shared their fossil finds with palaeontologists, but the hairy spheres they helped uncover in the permafrost were initially head-scratchers. Then paleontologist Grant Zazula realized the spheres were piles of fossilized ground squirrel feces.

Still, many of these samples languished in freezers for decades until Scott Cocker, who was working on his doctorate studying Pleistocene ground squirrels at the University of Alberta, began studying the ancient coprolites. “It was more just curiosity than anything,” Cocker says—a chance to try out the ancient DNA techniques he was learning in Murchie’s lab.

In general, DNA doesn’t age well—especially not for tens of thousands of years. In his previous work, Murchie had studied ancient DNA recovered from permafrost in the Yukon’s gold-rich Klondike region. That DNA had been preserved in ancient lake bed sediments, and it was degraded by water. DNA from ancient poop, however, tends to be much more intact. So when the pair defrosted their poop samples to examine the scat-stored DNA—“not the best smell,” Murchie admits—they found “a huge diversity of environmental DNA that we weren’t really expecting.” 

In the coprolite samples, which ranged from 17,000 years old to a staggering 700,000 years old, the scientists found genetic traces representing a rich ecosystem—grasses and flowering herbs and fungi, as well as a range of Pleistocene animals, everything from spiders and grasshoppers to mammoths, bison, and horses. 

How mammoth DNA ended up in squirrel poop, Cocker says, is less surprising than you might think. Today, modern ground squirrels are known to scavenge the carcasses of Canadian lynx and walrus, and he suggests ancient ground squirrels were probably doing the same to mammoths and other ice age megafauna. Taken together, Cocker adds, the squirrel scat DNA trove shows that “ground squirrels are this incredibly fascinating window into the mammoth-steppe ecosystem.”

Plus, by comparing what Ice Age squirrels ate to the diets of small mammals living in the Holocene, the scientists are revealing intricate details about how the environment changed through time. In Holocene-era coprolites, for instance, they’re finding more woody plants and fewer grasses, as well as an overall decline in animal diversity compared to the Pleistocene.

Laura Epp, who studies environmental genomics at Germany’s University of Konstanz and was not involved in the study, says scientists are increasingly realizing the power of poop to preserve DNA. “The whole world is full of this genomic data as soon as we start looking,” Epp says. “There are really a lot [of coprolites] that haven’t been touched that are great archives for any type of genomic work.”

She says scientists are routinely surprised by what can be found in fossilized feces. In Epp’s own research, for instance, which involved looking at the Pleistocene-era coprolites of a now extinct hyena, she found the mitochondrial DNA of a European woolly rhinoceros—the first time the species’ mitochondrial genome had been sequenced, regardless of the relative abundance of woolly rhinoceroses in the fossil record.

Despite their power, Epp says coprolites cannot provide a complete picture of the Ice Age landscape, because they only reflect what the animal that produced them had been eating and drinking. Nonetheless, she says ancient poop can provide a way to track how an environment changes over time, especially when combined with other independent environmental analyses, such as sediment samples.

Murchie agrees. Each poop offers a unique perspective on the landscape. “What we’re really extracting is a series of snapshots through time,” he says.

Ultimately, what the coprolites reveal is a familiar lesson: Ecosystems aren’t fixed. And as the planet faces down what is perhaps the largest climate shift since the Pleistocene-Holocene transition, even the humblest traces of the past can be a reminder of what the future holds. 

“I think we maybe forget how dynamic and changeable environments are, because it’s been so stable for so long,” Murchie says. “This work helps put into perspective how dramatically things can shift.”