GoKawiilGround squirrels go into a hibernation state called torpor for up to eight months. Credit: Image Professionals GmbH/Alamy
Ground squirrels spend many months in a winter slumber, and then awake ravenous and eat anything and everything in sight. A study of 700,000-year-old DNA from coprolites — fossilized poo — has now revealed that when ancient relatives of ground squirrels (Urocitellus sp.) woke up, they ate a diverse diet of plants, insects and carcasses of megafauna, including woolly mammoths, bison and big cats.
The DNA sequences, reported in a 9 June Nature Communications study1, reveal a previously unknown lineage of ground squirrel and, potentially, North America’s oldest mammoth DNA.
There are 13 species of ground squirrel in the genus Urocitellus, which are found mostly in northwestern North America and Asia. Ground squirrels are named for their earthen burrows where they can spend up to eight months of the year in a hibernation-like state called torpor.
When they emerge, “they’re desperate for protein and high-quality diet items”, says Bryan McLean, an evolutionary biologist at the University of North Carolina at Greensboro. “I’ve seen them eating roadkill individuals of the same species.”
The coprolites, or pellets of fossilized faeces, were found in the Klondike region of Canada. Credit: Scott Cocker
In the Klondike region of Canada’s Yukon territory, gold-mining practices that dissolve permafrost deposits using jets of water have also uncovered ancient ground squirrel burrows, filled with coprolites.
Tyler Murchie, a biomolecular archaeologist at the Hakai Institute in Heriot Bay, Canada, and his colleagues wondered if the coprolites would serve as a genetic archive of past ecosystems — through the lens of ground-squirrel diets.
The coprolites were dated to between around 700,000 to 17,000 years old, during a geological period known as the Pleistocene that was punctuated by ice ages, when mammoths, bison, horse and other megafauna roamed North America.
Still, Murchie was initially amazed when mitochondrial DNA sequences from this ‘Ice-Age cast’ turned up in the coprolites — as did sequences from rodents, bison and birds; invertebrates, including parasitic worms; and plants such as grasses and sedges. Big-cat DNA belonged to either the North American cheetah (Miracinonyx trumani), Murchie suspects, or to pumas (Puma concolor).
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