A time capsule that reveals an ecosystem from 700,000 years ago has been unearthed in permafrost that does not melt even in summer. It is the droppings of the Arctic ground squirrel (Urocitellus parryii). The squirrel's excrement, left after eating rotten meat or plants while alive, remained frozen underground. Scientists found DNA of mammoths and bison, as well as flowers and trees, inside it.
A team led by Hendrik Poinar, a professor in the Department of Anthropology at McMaster University, said on the 10th that they identified ecosystems dating back as far as 700,000 years through analysis of coprolites—fossilized droppings—of Arctic ground squirrels excavated from the permafrost of Yukon in northwestern Canada.
Ground squirrels are found mainly in northwestern North America and Asia. They are named for their habit of digging burrows underground. The findings were published the same day in the international journal Nature Communications.
◇ Oldest woolly mammoth DNA detected
A coprolite is a fossil in which animal droppings have hardened into a rock-like form. Because it retains DNA from the plants and animals eaten in life, it serves as a time capsule revealing ancient ecosystems. In English, it is called coprolite. In particular, Arctic ground squirrel burrows remain sealed in a frozen state in permafrost underground, preserving the genetic material inside the coprolites.
The Canadian team analyzed 13 Arctic ground squirrel coprolites excavated in central Yukon. The squirrel droppings contained DNA from various plants and animals. The coprolites were dated to an estimated 700,000 to 17,000 years ago, corresponding to the Pleistocene (2.58 million to 12,000 years ago), when ice ages recurred. It was a time when large animals such as mammoths, bison, and horses roamed the grasslands of North America.
As expected, the squirrel droppings contained DNA of various grassland animals, including woolly mammoths, steppe bison, horses, and reindeer. The 700,000-year-old woolly mammoth DNA was the oldest found in North America. The team dated the oldest coprolite using volcanic ash deposits located directly above the specimen.
Surprisingly, the squirrel droppings also contained DNA of predators such as the American cheetah and puma. The Arctic ground squirrel adapts to the cold climate by hibernating for up to eight months a year. When it wakes, it eats whatever animals or plants it finds in sight. It even eats the carcasses of its peers. Mikkel Pedersen of the University of Copenhagen said in Nature the same day, "Imagine the squirrels crawling out of the ground and starting to eat the carcasses scattered around," adding, "They were the zombies of the Pleistocene."
In the coprolites, the team also found mitochondrial DNA that can reveal the evolutionary process of ground squirrels. Mitochondria are small organelles in cells that produce energy and have their own DNA. Mitochondrial DNA, derived from the egg, is inherited only through the maternal line and is used as a clue to trace evolution. The mitochondrial DNA showed a genetic lineage different from that of the Arctic ground squirrels currently living in Yukon. The team said the Arctic ground squirrel split into several branches and evolved separately 420,000 years ago.
◇ As mammoths vanished, grasslands shifted to forests
From the ground squirrel coprolites, DNA of more than 200 plant species, including mugwort, JILGYUNGYI, and willow, was found. The team compared these results with DNA from rabbit coprolites from the Holocene, spanning 12,000 years ago to the present, to track ecosystem changes.
Decoding showed that the squirrel droppings contained much DNA of plants living in the cold tundra grasslands, while rabbit droppings contained abundant DNA of woody plants such as spruce and birch. Tyler Murchie of the Hakai Institute, the paper's first author, said, "Through coprolite fossils, we could see the transition from a great grassland ecosystem lush with flowering grasses to a landscape dense with forests."
The team said that during the Holocene, Yukon became covered with shrubs and moss because there were no large animal guilds—"ecosystem engineers"—to maintain the grasslands. Herbivores such as mammoths, horses, and bison nipped young leaves, preventing shrubs like willow and birch from taking hold. Thanks to that, the land remained open grassland rather than forest or thicket.
Also, when large animals such as mammoths or bison move, they compress and mix snow, soil, and moss layers. This process creates space for grasses to regrow. When such large herbivores disappear, moss and shrubs cover the ground, and grasses are pushed out. This is why some Russian scientists argue that if mammoths are restored and made to live in Siberia's permafrost, the grasslands can be revived.
References
Nature Communications (2026), DOI: https://doi.org/10.1038/s41467-026-72977-6