Paleontologists have described three previously unknown species of multituberculate mammals — named Camurodon borealis, Qayaqgruk peregrinus, and Kaniqsiqcosmodon polaris — that lived in polar forests about 73 million years ago. One of these species, Qayaqgruk peregrinus, is closely allied to a Mongolian group, representing the earliest direct evidence for multituberculate migration from Asia into North America and challenging assumptions that the Arctic was evolutionarily isolated.
A reconstruction of the Late Cretaceous paleoenvironment of Alaska. Image credit: James Havens.
Roughly in the size range between mice and rats, multituberculates were the longest-lived group of mammals known in Earth’s history.
These creatures 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 Chicxulub impact that killed all non-avian dinosaurs 66 million years ago.
Scientists have long wondered what allowed multituberculates to outlive many other mammals, and the three new species from Arctic offer a clue.
“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,” said Dr. Sarah Shelley, a paleontologist at the University of Lincoln.
The fossil teeth of Camurodon borealis, Qayaqgruk peregrinus, and Kaniqsiqcosmodon polaris were found in 73-million-year-old deposits of the Prince Creek Formation, located near the top of the world in the Arctic Circle.
Even then, the region experienced months of darkness in winter, freezing temperatures and likely seasonal food shortages. But these little creatures thrived.
“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 Dr. Patrick Druckenmiller, a paleontologist at the University of Alaska Fairbanks.
The researchers found striking differences in tooth shape among the three species, suggesting that they likely ate different foods.
Camurodon borealis had the teeth of herbivores, while Qayaqgruk peregrinus was an omnivore that probably fed on insects along with some plants.
Kaniqsiqcosmodon 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.
“Such adaptability might also have helped them survive the asteroid impact,” Dr. Shelley 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.”
The scientists also found that Qayaqgruk peregrinus is closely related to a species found in what is now Mongolia, suggesting Qayaqgruk peregrinus’ ancestors traveled from Asia to North America.
This dispersal likely happened about 92 million years ago, making it one of the earliest known examples of mammals crossing between the continents.
“This means there was a land corridor between Asia and North America for these little mammals to come through,” said Professor Jaelyn Eberle, curator at the University of Colorado Museum of Natural History.
“And this land bridge was already pretty active as far back as 90 million years ago.”
The discovery adds to the growing evidence that species have been migrating and reshaping ecosystems across continents for hundreds of millions of years.
“It really challenges how we think about native species,” Dr. 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.”
The discovery is reported in a paper in the Proceedings of the National Academy of Sciences.
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Sarah L. Shelley et al. 2026. Arctic ecosystems shaped mammalian dispersal and diversification before the Cretaceous-Paleogene mass extinction. PNAS 123 (22): e2601794123; doi: 10.1073/pnas.2601794123
