A new study reveals that small mammals not only survived but thrived in the ancient Arctic over 73 million years ago, coexisting with dinosaurs in northern Alaska. Researchers from the University of Colorado Boulder identified three previously unknown species—Camurodon borealis, Qayaqgruk peregrinus, and Kaniqsiqcosmodon polaris—from fossilized teeth found in the Prince Creek Formation. These multituberculates, rodent-like mammals unrelated to modern rodents, adapted to extreme polar conditions including months of winter darkness and limited food resources.

The Arctic during the Late Cretaceous was forested and ice-free, but still posed significant survival challenges. Dietary specialization allowed the three species to coexist: one primarily ate plants, another consumed insects and plants, and the third leaned toward vegetation. This niche partitioning helped reduce competition and supported biodiversity in a high-latitude ecosystem once thought to be biologically limited.

The findings challenge long-held assumptions that tropical regions were the sole centers of evolutionary innovation. Evidence of a close relative of Qayaqgruk peregrinus in Mongolia also suggests a land bridge between Asia and North America was active as early as 90 million years ago—pushing back the timeline for intercontinental mammal migration. The study, published in PNAS, highlights the resilience of mammals in the face of climatic stress and mass extinction.