The shape of the tooth suggests that Camurodon borealis was likely a herbivore. (Shelley et al. via SWNS)
By Stephen Beech
Three newly discovered species reveal how ancient mammals survived extreme weather conditions in the Arctic millions of years ago.
While the Arctic today may feel remote and desolate, scientists say that more than 70 million years ago it was a surprisingly lively place for some of Earth's ancient mammals.
Now three previously unknown species of rodent-like mammals that once scurried alongside dinosaurs in what is now northern Alaska have been identified by American researchers.
The team found that some of the newly discovered creatures' ancestors had traveled all the way from modern-day Mongolia, in East Asia, challenging a long-held assumption that the polar regions played only a minor role in evolution.
Study first author Sarah Shelley said: "While the polar regions don't host the same level of biodiversity as the tropics, they were still very active places for life to flourish, extending far back into deep time."
Shelley, now at the University of Lincoln in the UK, conducted the study as a postdoctoral researcher at the University of Colorado Boulder, with senior author Jaelyn Eberle, curator at the University of Colorado Museum of Natural History.
The team named the three species Camurodon borealis, which roughly translates to "Northern curved-tooth;" Qayaqgruk peregrinus, or "the little wandering hero;" and Kaniqsiqcosmodon polaris, meaning "polar frost ornamented tooth."
The researchers identified the animals using fossil teeth discovered in the Prince Creek Formation, located near the top of the world in the Arctic Circle.
The fossil site dates back 73 million years, according to the study published in the journal Proceedings of the National Academy of Sciences (PNAS).
Even then, the region experienced months of darkness in winter, freezing temperatures and likely seasonal food shortages. But these little creatures thrived.
Co-author Patrick Druckenmiller, from the University of Alaska in Fairbanks, said: "These three new mammal species add to a growing body of evidence that this ancient arctic region was home to unique, polar-adapted species."
The Colville River image shows field camp on a gravel bar in the middle of the river, while the small orange boat is pulled up along the far bank at an active fossil locality. (Shelley et al. via SWNS)
He said all three animals belong to an extinct mammal group called multituberculates.
In the size range between mice and rats, multituberculates were the longest-lived group of mammals known in Earth's history.
They persisted for more than 100 million years, from the Jurassic Period to the end of the Eocene Epoch about 35 million years ago.
They even survived the asteroid impact that killed all non-avian dinosaurs.
By comparison, modern humans have existed for only about 300,000 years.
Scientists have long wondered what allowed multituberculates to outlive many other mammals.
Now the teeth offer a clue.
The research team found striking differences in tooth shape among the three species, suggesting that they likely ate different foods.
They explained that C. borealis had the teeth of herbivores, while Q. peregrinus was an omnivore that probably fed on insects along with some plants.
K. polaris also appeared to have been an omnivore, but might have eaten mostly plants.
In a region with limited food, the ability to evolve and carve out their own diets might have helped different multituberculate species coexist, according to the research team.
Shelley says such adaptability might also have helped them survive the asteroid impact.
She said: "There's a lot of diversity in the multituberculate group.
"They lived for an incredibly long time, and I think they can reveal a lot about the resilience of mammals, not just to the mass extinction, but also to climatic stresses that many organisms are facing today."
Shelley says the discovery also helps paint a more complete picture of the ancient Arctic.
The team found that Q. peregrinus, named after a legendary hero, Qayaq, in the Alaskan Inuit culture, is closely related to a species found in what is now Mongolia, suggesting Q. peregrinus' ancestors traveled from Asia to North America.
Shelley estimated that this dispersal happened about 92 million years ago, making it one of the earliest known examples of mammals crossing between the continents.
Eberle said: "This means there was a land corridor between Asia and North America for these little mammals to come through.
"And this land bridge was already pretty active as far back as 90 million years ago."
The discovery adds to growing evidence that species have been migrating and reshaping ecosystems across continents for hundreds of millions of years.
Shelley added: "It really challenges how we think about native species.
"Deep time reminds us that a place is not just a point on a map, but a long, layered history of landscapes and inhabitants."
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