Mouse-Like Mammals Ruled the Ancient Arctic Before Dinosaurs Vanished!

In a groundbreaking 2025 study published in Science Advances, paleontologists have revealed that tiny, mouse-like mammals dominated the polar forests of Arctic Alaska and Canada during the final 10 million years of the Cretaceous — thriving in darkness and cold while giant dinosaurs ruled the rest of the world.

The fossils, recovered from the Prince Creek Formation in northern Alaska and the Kanguk Formation on Banks Island, include dozens of jaws, teeth, and partial skeletons of mulтιтuberculates and early eutherian mammals. These creatures, no larger than a modern chipmunk, were the most abundant vertebrates at these high-laтιтude sites. Their teeth show specialized diets ranging from seeds and insects to fungi — evidence of a thriving, self-sustaining ecosystem beneath the midnight sun.

Lead author Dr. Jaelyn Eberle (University of Colorado) states: “These small mammals were not just surviving; they were thriving. In the Arctic fossil record, they outnumber dinosaur bones by a wide margin.” The animals possessed dense fur and likely hibernated or entered torpor to endure months of winter darkness and sub-zero temperatures.

This discovery upends the traditional view that mammals remained small, marginal, and nocturnal until the dinosaurs disappeared 66 million years ago. Instead, the Arctic served as a cradle of mammalian diversity and ecological dominance long before the asteroid impact. The same lineages later exploded in size and variety after the extinction, suggesting the polar regions pre-adapted mammals for the post-dinosaur world.

As more Arctic sites are explored, these “Arctic mice” promise to rewrite the final chapter of the Age of Dinosaurs — proving that the future rulers of Earth were already in charge at the top of the world.