Ancient Ground Squirrel Droppings in Yukon Permafrost Reveal Arctic Ecosystem History

Researchers led by Tyler Murchie of the Hakai Institute and McMaster University analyzed permafrost-preserved coprolites from 13 Arctic ground squirrel burrows in the Yukon's central Klondike region, with samples dating from approximately 17,000 to 700,000 years ago. The fecal pellets, roughly 1–2 centimeters long, yielded environmental DNA from more than 200 plant groups, microbes, insects including parasitic worms, birds, bats, rodents, and large megafauna such as woolly mammoths, horses, steppe bison, grey wolves, and a big cat identified as either the extinct North American cheetah or a puma. The team reconstructed over 18 mitochondrial genomes from ground squirrels, woolly mammoths, horses, and steppe bison, with a separate forthcoming study expected to detail the mammoth genomes further. The DNA evidence confirms that ancient ground squirrels were opportunistic omnivores that scavenged carcasses of megafauna in addition to eating plants and insects — behavior consistent with modern Arctic ground squirrels. A key evolutionary finding was the identification of a 700,000-year-old ground squirrel lineage no longer present in the Yukon, whose closest relatives today live in western Siberia, overturning the prior assumption that fossil squirrels from that era belonged to the same species found in the Yukon today. Researchers also noted that the coprolites appear to preserve ancient DNA better than bones or surrounding permafrost, and warned that rapid permafrost thaw driven by climate change is already destroying some of these irreplaceable sites.