Mammals
Mountain Beaver
Aplodontia rufa · also called sewellel, boomer
Emerging from a burrow dug close to a mountain stream, a mountain beaver forages on ferns and shrubs, a species that despite its name shares no close relation to true beavers and is instead considered the most primitive rodent still living on Earth today.
Overview
The mountain beaver, Aplodontia rufa, is a stocky, nearly tailless rodent native to forest and mountain habitat across parts of the Pacific coast of North America. Its status as the most evolutionarily primitive living rodent, misleading common name unrelated to true beavers, and unusual physiological need for frequent access to water make it one of the more biologically fascinating small mammals found anywhere in North America.
A living fossil hiding in plain sight
Despite a name that suggests a small relative of the true beaver, the mountain beaver instead represents a far older, more primitive branch of the rodent family tree, a genuine living link to the ancestral rodents that came long before most modern species evolved.
Status
Least Concern overall, though one geographically isolated subspecies faces more serious conservation concern than the species as a whole.
Mountain Beaver: common questions
Is the mountain beaver actually a beaver?
No, despite sharing part of its common name, this species is not closely related to true beavers at all, belonging instead to an entirely separate and much older rodent lineage that happens to share a superficial resemblance and a preference for living near water.
Why is the mountain beaver considered so primitive?
This species is widely regarded by researchers as the most evolutionarily primitive living rodent species, retaining a number of ancestral anatomical features that have been lost in nearly all other modern rodent species over millions of years of evolution.
Why does the mountain beaver need to live so close to water?
This species must drink water frequently and cannot survive far from a reliable source, since its body is comparatively inefficient at conserving water, a physiological limitation that restricts it to habitat within easy reach of streams or other water sources.
What does the mountain beaver look like?
This species has a stocky, compact body with only a very short, barely visible tail, a build quite different from that of true beavers, more closely resembling a large, tailless guinea pig than the flat-tailed, aquatic true beaver its name suggests.