A new study drew on fossilized squirrel droppings up to 700,000 years old, containing ancient DNA, to reveal important details about the Arctic’s evolutionary history.
These fossilized droppings (coprolites) were preserved for millennia in the ‘permafrost’ (permanently frozen ground) of Yukon, Canada, and the DNA found in them is among the oldest ever recovered and sequenced.
The DNA analyzed comes from hundreds of plant species, insects, microbes and large mammals, such as woolly mammoths, horses and steppe bison.
The investigation, led by Canada’s Hakai Institute and conducted with permission from the Tr’ondëk Hwëch’in Nation, on whose traditional territory it took place, analyzed thirteen samples of Arctic ground squirrel coprolites (Urocitellus parryii) dated between 30,000 and 700,000 years ago, according to Tuesday’s report by the EFE agency.
Coprolites can preserve a variety of biomolecules from ancient animals, including DNA from both the animal that produced them and the surrounding environment, although they are used less often in studies than bones or sediments.
In Arctic regions, Arctic ground squirrel burrows can remain frozen and sealed for thousands of years, enabling genetic material to be preserved in the coprolites.
The team extracted a substantial amount of ancient environmental DNA from the feces, roughly the size of a rabbit’s droppings, and then reconstructed more than 18 mitochondrial genomes of ground squirrels, woolly mammoths, horses and steppe bison.
They also found evidence of other rodents and predators, such as gray wolves, large cats — whether pumas or cheetahs — and more than 200 groups of plants.
The ground squirrel coprolites “preserve genetic snapshots of extraordinary diversity from ancient Beringia, making them an exceptional repository” for understanding evolutionary and ecological changes of a remote past, according to Hendrik Poinar, one of the paper’s authors.
These remnants help reconstruct paleo-environments, “providing information about environmental changes, the evolution of megafauna, their dispersal and, ultimately, their extinction,” added a researcher from McMaster University (Canada).
Today’s Yukon Arctic ground squirrels behave like scavenging rats, gathering large amounts of plant debris, bones, and seeds, and transporting them back to their burrows.
The squirrels that left these traces thousands of years ago are genetically distinct from today’s squirrels, but their behavior seems to have been similar.
Coprolites offer a glimpse of landscape changes over hundreds of thousands of years and pave the way for numerous future discoveries. They also seem to preserve ancient DNA even better than bones or the surrounding permafrost.
The authors noted that some DNA may have adhered to the coprolite’s surface later and that reference databases can affect species identification.
In this regard, they believe that more investigations are needed to refine and expand these techniques, although the study results suggest that permafrost coprolites can be effectively used to obtain high-resolution snapshots of prehistoric environments and complement knowledge derived from ancient sedimentary and skeletal DNA.
