More than 70 million years ago, the Arctic wasn't a frozen wasteland—it was a surprisingly vibrant home for creatures that would astound modern paleontologists with their resilience and diversity. University of Colorado Boulder researchers have now identified three previously unknown mammal species that thrived in what is now northern Alaska, challenging long-held assumptions about how life flourished in Earth's polar regions.
The three species—Camurodon borealis (Northern curved-tooth), Qayaqgruk peregrinus (the little wandering hero), and Kaniqsiqcosmodon polaris (polar frost ornamented tooth)—were discovered through fossil teeth unearthed in the Prince Creek Formation near the Arctic Circle, dating back 73 million years. At that time, the region experienced months of unbroken darkness each winter, freezing temperatures, and seasonal food scarcity. Yet these rodent-like creatures, which belonged to an extinct group called multituberculates, not only survived but thrived in conditions that would challenge most modern animals.
All three species ranged in size between mice and rats, but their most revealing feature lay in their teeth. By examining tooth shape and structure, Sarah Shelley, the paper's first author from the University of Lincoln in the U.K., and her colleagues at CU Boulder discovered something unexpected: each species had evolved to eat different foods. C. borealis was a herbivore, while Q. peregrinus was an omnivore that likely hunted insects alongside foraging for plants. K. polaris was also omnivorous but probably leaned heavily on vegetation. In an environment with limited resources, this dietary specialization allowed multiple species to coexist without competing directly for survival.
The discovery offers a window into why multituberculates became the longest-lived mammal group in Earth's history, persisting for more than 100 million years—from the Jurassic Period until about 35 million years ago. They didn't just outlast most of their contemporaries; they survived the asteroid impact that wiped out all non-avian dinosaurs. "There's a lot of diversity in the multituberculate group," Shelley explained. "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."
Perhaps most striking is what these Arctic fossils reveal about ancient migration patterns. Q. peregrinus is closely related to a species found in present-day Mongolia, suggesting that its ancestors made the remarkable journey from Asia to North America around 92 million years ago—one of the earliest known examples of mammals crossing between the continents. This discovery provides concrete evidence that a land corridor connected Asia and North America far earlier and remained active much longer than previously thought, reshaping our understanding of how life moved and adapted across a dynamic ancient world.
The study, published in the Proceedings of the National Academy of Sciences, adds to growing evidence that polar regions were never evolutionary backwaters. While they may not host the biodiversity of tropical zones, they were—and remain—uniquely active places where life found ingenious ways to flourish against the odds.