Fossil of hamster-sized mammal found on the Pacific Coast.

A research team from the University of Washington has made an exciting discovery by identifying a new species of ancient mammal that lived alongside dinosaurs on the Pacific Coast.

3 min readUW News
Fossil of hamster-sized mammal found on the Pacific Coast.
An illustration of Cimolodon desosai on the tree with a fruit in its mouth. It was about the size of a golden hamster. It likely scampered on the ground and in the trees and ate fruits and insects. Photo: Andrey Atuchin
From UW News

Mammals and dinosaurs coexisted on Earth until a catastrophic event 66 million years ago killed 75% of life on the planet. Despite the devastation, some animals survived, including rodent-like mammals in the Cimolodon genus. These creatures are part of the multituberculates, a group that arose during the Jurassic Period and survived over 100 million years before going extinct. Studying these animals helps researchers better understand how mammals survived the mass extinction event and then diversified into the variety of mammals around today.

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Briefing

Source
UW News
Published
April 24, 2026