University of Washington Researchers Identify Hamster Sized Mammal Cimolodon Desosai from 75 Million Year Old Fossil

University of Washington scientists identify Cimolodon desosai, a hamster sized mammal that coexisted with dinosaurs and survived mass extinction.

By: AXL Media

Published: Apr 24, 2026, 6:14 AM EDT

Source: Information for this report was sourced from EurekAlert!

A Remarkable Discovery From the Age of Reptiles

The unveiling of Cimolodon desosai represents a significant milestone in our understanding of the Late Cretaceous epoch, a time dominated by dinosaurs. According to Gregory Wilson Mantilla, a biology professor at the University of Washington, this newly identified species was roughly the size of a golden hamster and occupied a unique ecological niche. The creature, which scampered through both terrestrial and arboreal habitats, likely sustained itself on a diet of insects and fruits. This discovery provides a rare window into the lives of the smaller, nimble mammals that shared the Earth with massive reptiles before the great extinction.

The Resilience of the Multituberculate Lineage

The species belongs to the multituberculates, a prolific group of rodent like mammals that emerged during the Jurassic Period. These animals displayed remarkable evolutionary staying power, persisting for more than 100 million years. According to Wilson Mantilla, the ancestors of Cimolodon desosai possessed two specific advantages that were instrumental for survival: a small physical stature and an omnivorous diet. These traits allowed the genus to navigate the ecological collapse that occurred 66 million years ago, eventually paving the way for the diverse mammalian populations that inhabit the modern world.

Recovering a Rare Skeleton in Baja California

Finding fossils at the Baja California research site is an arduous task, making the 2009 discovery of this specimen particularly noteworthy. While many prehistoric mammals are identified solely by isolated teeth, this find included a skull, jaws, and critical skeletal elements such as a femur and an ulna. Wilson Mantilla noted that the discovery began when a field assistant spotted a single tooth emerging from a rock. Upon further inspection, the team realized the crack contained a much more substantial portion of the animal, allowing for a comprehensive analysis of its physical structure.