In a deep frozen burrow in the Yukon, ground squirrel droppings the size of rabbit pellets have revealed a genetic blueprint of the Arctic that existed up to 700,000 years ago—and it looks nothing like the landscape we know today. Researchers analyzing permafrost samples from burrows spanning multiple glacial periods have extracted ancient environmental DNA (aeDNA) from dozens of species, reassembling complete mitochondrial genomes from woolly mammoths, horses, steppe bison, and ground squirrels themselves. This discovery, published in Nature Communications and conducted by scientists at McMaster University, the Hakai Institute, the University of Alberta, and other institutions, represents some of the oldest ancient DNA ever successfully recovered and sequenced.
The samples, which ranged from 30,000 to approximately 700,000 years old, revealed far more than just a list of animals. The Arctic ground squirrel, Urocitellus parryii, acts as a natural archive keeper. An opportunistic forager with a wide-ranging diet—plants, fungi, insects, carrion, even whale meat—the species collects bits of material from across the landscape and stockpiles them in burrows where they hibernate for up to seven months in frozen ground. Over millennia, these droppings preserved remarkably detailed genetic snapshots of ancient Beringia, the vast region spanning the Yukon and Alaska. The data uncovered evidence of gray wolves, a big cat species (either a cougar or an American cheetah), more than 200 groups of plants, and several other rodent and predator species that no longer inhabit those regions.
Perhaps the most striking finding was what the DNA revealed about ground squirrels themselves. Fossil remains from central Yukon had long been assumed to belong to the same species living in northern and southern Yukon today. But genetic analysis showed that assumption was wrong. Researchers discovered previously unknown genetic diversity among Arctic ground squirrels, including one ancient lineage dating back 700,000 years that disappeared from the Yukon entirely. Its closest living relatives today are found only in western Siberia—a geographic separation that speaks to how dramatically the Arctic landscape and animal distributions have shifted.
"Ground squirrel coprolites preserve remarkably diverse genetic snapshots of ancient Beringia, making them exceptional repositories for understanding evolutionary and ecological change through the deep past," says Hendrik Poinar, evolutionary geneticist and director of the McMaster Ancient DNA Center, where much of the analysis took place. This work helps scientists reconstruct ancient environments in far deeper time than previously possible, providing insights into how species responded to drastic climatic shifts and ultimately disappeared or migrated.
The findings carry implications for understanding how animals and plants may adapt—or fail to adapt—to our warming world today. As Poinar notes, "We can look at genes under selection due to climate change in the past and that may help us think about how animals today may, or may not, adapt to our current warming climate." Remarkably, the fossil droppings appear to preserve ancient DNA even better than bones or surrounding permafrost. Researchers say the material holds far more ecological and evolutionary detail than any single study can cover, opening the door to discoveries yet to come from these frozen archives buried beneath the Yukon.