Old squirrel poop doesn’t stink. At least not at first.
But that changes when you start breaking down the pellets. Their fusion made it clear that these were not mineralized or stony fossils, says biomolecular archaeologist Tyler Murchie of the Hakai Institute in Canada. “There is no doubt about it,” he said. “It’s a lab that smells like poop.”
Fresh fecal odor is a sign of science. The pellets contain DNA fragments from the diet of squirrels that paint a image of animal ecosystems with new detailsMurchie and colleagues report June 9 in Natural communications.
Fecal pellets are among the many ancient remains found during gold mining operations, Murchie says. By melting the permafrost, miners expose gold as well as valuable bones and mummified remains of ancient creatures.
There are bones of mammoths and steppe bison, Murchie says, and as the work progresses, “you see these big outcrops on the valley walls, there are all these little pockets.” These holes are the remains of ground squirrel burrows (genus Urocitellus). The burrows are literally frozen in time. “They have small latrines, tunnel networks and food caches,” Murchie explains.
Ancient gophers were wonderful assistants in paleontology. “They really function as little naturalists or archivists, roaming the landscape like pack rats, gathering all these bits of plant matter, seeds, leaves, twigs, etc., bones,” Murchie says. But while scientists had carefully cataloged the contents of the burrows, no one had looked at the frozen droppings left by the squirrels.
The researchers plugged their noses, thawed the pellets and extracted DNA from 13 Yukon squirrel coprolites. The oldest droppings were found to be nearly 700,000 years old, while others are between 80,000 and 17,000 years old, spanning the Pleistocene epoch.
Scientists generally assume that Pleistocene squirrels were the same as those still found in the Yukon today. But “the species we thought we were don’t actually seem to be the ones that exist today,” Murchie says. “There has been a sort of renewal of the population.” The oldest sample, almost 700,000 years old, could be a new species. “It’s in its own evolutionary branch,” he says. “The closest thing to it are the squirrels that are currently in China.”
The poop also held other surprises. “I thought the DNA would be mostly from the squirrel and its gut microbiome,” Murchie says. But there were also fragments of the squirrels’ diet.
Ground squirrels are not picky eaters, and their genetic material comes from grasses, willows, beetles, grasshoppers, woolly mammoths, steppe bison, wolves, ancient horses, and many other species.
There probably weren’t packs of ground squirrels voraciously chasing the mammoths, says Jaquelyn Gill, a paleoecologist at the University of Maine in Orono, who was not involved in the study. Instead, the squirrels were probably scavenging. “It could have been a part of their diet. They could have chewed bones for [the] source of calcium,” she says.
Today, rodents frequently do the same thing. “I remember seeing one on my fence eating a bone,” Murchie says. “It was definitely a different perspective on them after that.” Their omnivorous tendencies allowed Murchie and his colleagues to reconstruct the mitochondrial genomes of 24 animals, including 12 from the squirrels themselves, a snowshoe hare used as a control, two bison, three horses and six mammoths.
Other species in the droppings provide a detailed picture of the ecosystem, Gill says. “A mammoth bone will tell you there was a mammoth here,” she said. “These ground squirrel coprolites tell you that we had a ground squirrel here that ate these plants, lived among these insects and shared the landscape.”
And while it’s easy to want to study a mammoth tusk, it’s a little harder to see the promise in scat, she says. “I think you have to have a little imagination and maybe a little humility.”
