Tiny fossil tooth from Alaska are altering how scientists view mammal life and migration within the historical Arctic.
At this time’s Arctic is likely one of the harshest and least biodiverse locations on Earth, however in the course of the age of dinosaurs it was residence to a surprisingly wealthy neighborhood of mammals. A brand new fossil discovery suggests this historical polar ecosystem was not an remoted evolutionary outpost however an vital crossroads the place species adapted, diversified, and even migrated between continents.
In a new study published in the Proceedings of the National Academy of Sciences (PNAS), scientists from the University of Colorado Boulder and collaborating institutions describe three previously unknown species of rodent-like mammals that lived in what is now northern Alaska more than 70 million years ago.
Their analysis indicates that the ancestors of some of these mammals traveled from what is now Mongolia in East Asia, challenging the long-held assumption that the polar regions played only a minor role in mammal evolution.
“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,” says Sarah Shelley, the paper’s first author at the University of Lincoln in the U.K. She conducted the study as a postdoctoral researcher at CU Boulder with senior author Jaelyn Eberle, a professor in the Department of Geological Sciences and curator at the University of Colorado Museum of Natural History.
Teeth reveal Arctic mammals
Shelley, Eberle, and colleagues 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 animals were identified from fossil teeth found in the Prince Creek Formation, a site inside the Arctic Circle near the top of the world. The fossils are about 73 million years old. At that time, the region still had months of winter darkness, freezing conditions, and likely seasonal food shortages. Even so, these small mammals managed to survive there.
“These three new mammal species add to a growing body of evidence that this ancient arctic region was home to unique, polar-adapted species,” said Patrick Druckenmiller, a coauthor at the University of Alaska Fairbanks.
Diets show survival strategies
All three species belonged to an extinct group of mammals known as multituberculates. These animals were roughly mouse-sized to rat-sized and were the longest-lived mammal group known from Earth’s history. They survived for more than 100 million years, from the Jurassic Period through the end of the Eocene Epoch about 35 million years ago. They also lived through the asteroid impact that wiped out all nonavian dinosaurs. By comparison, modern humans (Homo sapiens) have existed for only about 300,000 years.
Scientists have long asked why multituberculates endured for so long, and the newly studied teeth offered an important clue.
The three species had noticeably different tooth shapes, suggesting that they likely ate different foods. C. borealis had teeth suited to herbivores, while Q. peregrinus was an omnivore that probably ate insects as well as some plants. K. polaris also appeared to be an omnivore, though it may have relied mostly on plants.
In a place where food could be scarce, the ability to specialize in different diets may have allowed several multituberculate species to live side by side. Shelley said that same flexibility may also have helped them survive the asteroid impact.
“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,” she said.
Ancient migration reshapes history
The discovery also adds new detail to the history of the ancient Arctic.
The team found that Q. peregrinus, named for Qayaq, a legendary hero in Alaskan Inuit culture, is closely related to a species from what is now Mongolia. That connection suggests the ancestors of Q. peregrinus moved from Asia into North America. Shelley estimated that this migration happened about 92 million years ago, making it one of the earliest known examples of mammals moving between the two continents.
“This means there was a land corridor between Asia and North America for these little mammals to come through,” Eberle said. “And this land bridge was already pretty active as far back as 90 million years ago.”
The finding strengthens evidence that species have been moving across continents and reshaping ecosystems for hundreds of millions of years.
“It really challenges how we think about native species,” Shelley said. “Deep time reminds us that a place is not just a point on a map, but a long, layered history of landscapes and inhabitants.”
Reference: “Arctic ecosystems shaped mammalian dispersal and diversification before the Cretaceous–Paleogene mass extinction” by Sarah L. Shelley, Jaelyn J. Eberle, Gregory M. Erickson and Patrick S. Druckenmiller, 18 May 2026, Proceedings of the National Academy of Sciences.
DOI: 10.1073/pnas.2601794123
This research was supported by NSF grants EAR 1226730 (to G.M.E. and P.S.D.), 1736515 (to J.J.E., G.M.E., and P.S.D.) and a planning grant from the Council on Research on Creativity at FSU (to G.M.E.).
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