Mountain Beavers: Living Fossils You have probably heard some animals, like sharks, insects, certain fish, and various types of lizards, referred to as "living fossils." Sometimes the term refers to an animal that is not closely related to any other animal or has survived extinction on at least one occasion, but sometimes people use the term "living fossil" to refer to any animal that has been around for a very long time. The Mountain Beaver, as the most ancient living rodent, is an example of a living fossil no matter how the term is used. Mountain Beavers are not Beavers Although they are called beavers, Mountain Beavers are not closely related to other beaver species. Both the North American beaver and the Eurasian beaver are members of the genus Castor, whereas the mountain beaver is in the genus Aplodontia. Not only is the Mountain Beaver unrelated to other beavers, it is the only living animal in its genus, its closest relatives all having gone extinct. This makes it a living fossil by many standards, but there are other features that point to the long history of the mountain beaver. For example, its jaw and the muscles that control the jaw are arranged in a manner unlike any other living rodent. The Mountain Beaver's closest living relatives are squirrels. Habitat and Names Like many other living fossils, Mountain Beavers are highly adapted and very well suited to survive as a species. Currently, there are seven subspecies of Mountain Beaver, and they can be found along the Pacific coast of North America from British Columbia, Canada to the Sierra Nevada mountains in California. Due to its diet and biological adaptations, the Mountain Beaver is specially suited to this rainy area and would not be likely to survive in drier climates. Historically, the Chinook people made cloaks and other items from the pelts of mountain beavers. Such a pelt was called a sewellel, and as a result, sometimes the Mountain Beaver is called a Sewellel Beaver. Other names for the Mountain Beaver include: Giant Mole, Whistler, Boomer, Ground Bear, and Aplodontia. Mountain Beavers, Humans, and Other Animals In some areas, Mountain Beavers are considered a pest because they are abundant and may eat plants and small trees planted in gardens. Otherwise, Mountain Beavers chiefly eat ferns, with other plants supplementing their diet. The beavers have a number of predators, including cougars, bobcats, coyotes, and owls. They protect themselves from predators by building elaborate tunnel systems in which they live and store food. Other small animals have been known to make use of these tunnel systems, as well. Another interesting fact about Mountain Beavers: they provide a home to the oldest and largest species of flea discovered to date. Mountain Beavers themselves are usually between 12 and 20 inches in length. Their fleas have been found to grow up to one third of an inch in length. The Reclusive Mountain Beaver Despite their commonality, Mountain Beavers tend to stay out of sight in areas inhabited by humans because they do not often travel far from their burrows. One account claims that Lewis and Clark, on their famous voyage of discovery, attempted but were unable to find a live Mountain Beaver. In addition to avoiding humans, Mountain Beavers are reported to be quite antisocial in general. Although their territories may overlap, they do not associate with other beavers, and mating pairs do not remain together for any length of time. Due to these reclusive habits, even natives of the Pacific region of North America may never see a Mountain Beaver in the wild, but they are likely to continue flourishing there.