Frozen Squirrel Scat Reveals Ancient Ecosystem of Woolly Mammoths and Big Cats

Ancient DNA from Rodent Droppings Unveils Ice-Age Ecosystem

Scientists have reconstructed a rich and complex ecosystem stretching back 700,000 years by analyzing DNA preserved in frozen feces of Arctic ground squirrels. The study, published in a recent issue of Current Biology, reveals a diverse community of ice-age megafauna including woolly mammoths, steppe bison, horses, grey wolves, and a large cat—either an American cheetah or a cougar—that once roamed the Beringian landscape.

Arctic ground squirrels (Urocitellus parryii), small rodents about 40 centimeters long, inhabit cold regions of North America and Siberia. These areas were connected by a land bridge in the past, forming a region known as Beringia. The squirrels hibernate for about eight months each year, and during their active four-month period, they gather food and bring it back to their burrows. This behavior makes them natural archivists, as their burrows often contain a wealth of faecal pellets and food caches.

Natural Archivists in Permafrost

Lead author Tyler Murchie of the Hakai Institute in Campbell River, Canada, explains that the squirrels' burrows preserve a snapshot of the environment. The team examined preserved faeces, known as coprolites, from 13 Arctic ground squirrel burrows in the central Yukon, Canada, that were frozen in permafrost. The burrows dated to between about 30,000 and 700,000 years ago. Each coprolite is about 1 to 2 centimeters long.

From these droppings, the team extracted DNA belonging to a wide range of organisms. The genetic material 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. “It’s the whole cast of organisms that lived in the Beringian ice-age ecosystem,” says Murchie.

Omnivorous Squirrels as Ecosystem Samplers

While one might assume ground squirrels primarily eat nuts and seeds, the study reveals they are quite omnivorous. “They’re actually quite omnivorous, almost like little bears. There are reports of ground squirrels eating carcasses of moose and lynx, so the fact that we find all of these large animals in their coprolites isn’t actually that surprising,” Murchie notes. This scavenging behavior allowed the squirrels to inadvertently sample the DNA of large mammals they encountered.

The researchers were able to reconstruct mitochondrial genomes of many animals from different points in time, providing a temporal view of the ecosystem's changes. The findings offer a unique window into the biodiversity of Beringia during the Pleistocene, a period marked by dramatic climate shifts.

Implications for Understanding Past Ecosystems

This method of using ancient DNA from rodent coprolites opens new avenues for studying past ecosystems without relying on rare fossils or large-scale excavations. It provides a high-resolution picture of species interactions and environmental conditions. The study also highlights the importance of permafrost preservation for ancient DNA research.

The research team plans to expand their analysis to other regions and time periods, potentially uncovering more details about how ecosystems responded to past climate changes. As permafrost thaws due to modern climate change, such ancient DNA archives may be lost, making this work timely.

In summary, the frozen scat of Arctic ground squirrels has proven to be an unexpected treasure trove of ancient DNA, revealing a vibrant ice-age community that included some of the most iconic megafauna of the Pleistocene.

This article is based on reporting by New Scientist. Read the original article.