Arctic ground squirrels have preserved a 700,000-year record of ancient ecosystems within their fossilized droppings, or coprolites, found in Yukon permafrost. A study published in Nature Communications reveals that these samples contain environmental DNA from plants, insects, and megafauna like mammoths and horses, offering a more resilient record of prehistoric life than traditional bone fossils.
How Coprolites Outperform Traditional Fossils
Fossilized feces act as a superior repository for ancient environmental DNA (eDNA) compared to skeletal remains, according to the research team led by McMaster University evolutionary geneticist Hendrik Poinar. While bones and teeth are often sought after for analysis, they are susceptible to chemical degradation. In contrast, the study found that squirrel coprolites effectively "seal" genetic material from the surrounding environment. Because Arctic ground squirrels are opportunistic feeders that collect seeds, bones, and plant matter for their seven-month hibernation cycles, their latrines serve as concentrated, multi-species biological archives.
What Future DNA Sequencing Reveals About Ancient Migration
The sequencing of these samples has identified 18 unique mitochondrial genomes, providing a roadmap for tracking how species shifted their ranges during past glacial periods. Lead author Tyler Murchie noted in a statement that the diversity found within the droppings indicates that some squirrel lineages lived in regions far removed from their current Yukon habitats. By comparing these genetic markers with modern records, scientists can reconstruct how megafauna—including bison and horses—responded to previous climate shifts. This data provides a baseline for predicting how current Arctic species might adapt as modern temperatures rise.
How Researchers Extract Data from Frozen Samples
Extracting usable DNA from material that is hundreds of thousands of years old requires precise handling to avoid modern contamination. According to the study, researchers thaw the coprolites—which are roughly the size of rabbit droppings—and apply advanced sequencing techniques to differentiate between the squirrel’s own gut microbiome and the environmental DNA they consumed. While the team initially expected to find only internal biological data, the results included genetic traces of predators like wolves and big cats, suggesting the squirrels scavenged on carcasses near their den sites.
Frequently Asked Questions
- Why is squirrel poop better than mammoth bones? It preserves a wider variety of environmental DNA, including plants and insects, which are rarely found in the same state of preservation as large vertebrate fossils.
- How old is the oldest DNA found in these samples? The study analyzed samples spanning up to 700,000 years, providing a timeline that reaches back through multiple glacial cycles.
- Can this help us understand climate change today? Yes. By documenting how animals and plants migrated or went extinct during past warming and cooling cycles, researchers gain context for modern biodiversity loss.
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