Arctic Mulтιтuberculate Fossils Reveal Rodent-Like Mammals Were Already Thriving 73 Million Years Ago, Long Before Dinosaur Extinction

In a May 2026 PNAS study, paleontologists have described three new mulтιтuberculate species from Alaska’s Prince Creek Formation (~73 Ma, paleolaтιтude 80–85°N), proving that rodent-like mammals were already diverse and ecologically dominant in polar forests millions of years before the K-Pg extinction wiped out the non-avian dinosaurs.

Led by Sarah Shelley (University of Lincoln) and colleagues, the team named Camurodon borealis (“northern curved-tooth”), Qayaqgruk peregrinus (“little wandering hero”), and Kaniqsiqcosmodon polaris (“polar frost ornamented tooth”). These tiny, herbivorous mulтιтuberculates—known for their multi-cusped teeth—flourished in a high-laтιтude ecosystem of conifer forests, ferns, and seasonal darkness.

Crucially, one species shows direct Asian affinities, providing the earliest evidence of mulтιтuberculate migration across a northern land corridor. The Arctic was not an evolutionary backwater but a dynamic “cradle and corridor” that fostered diversification and enabled dispersal between Asia and North America.

These adaptations—likely including cold tolerance and flexible diets—help explain why mulтιтuberculates survived the Chicxulub impact and briefly dominated post-extinction faunas before true rodents took over. The discovery overturns the view that mammals were merely “waiting in the wings” until dinosaurs vanished; instead, they were already sophisticated, widespread, and resilient players in Late Cretaceous ecosystems.

The Prince Creek fossils demonstrate that the Age of Mammals began long before the Age of Dinosaurs ended.