The mountain beaver (''Aplodontia rufa'')Other names include mountain boomer, ground bear, giant mole, gehalis, lesser sasquatch, sewellel, suwellel, showhurll, showtl, and showte, as well as a number of

Chinookan The Chinookan languages were a small family of languages spoken in Oregon and Washington along the Columbia River by Chinook peoples. Although the last known native speaker of any Chinookan language died in 2012, the 2009-2013 American Community ...

and other Native American terms; "mountain boomer" is a misnomer, and the animal does not make the characteristic tail slapping sound of the true beaver species. See Carraway and Verts, 1993. Lewis and Clark originally called the animal "sewellel", a misunderstanding of the Chinook word "she-wal-lal", the name for garments made from the skin of the creature. See Borrecco and Anderson, 1980. is a North American

rodent Rodents (from Latin , 'to gnaw') are mammals of the order Rodentia (), which are characterized by a single pair of continuously growing incisors in each of the upper and lower jaws. About 40% of all mammal species are rodents. They are n ...

. It is the only living member of its genus, ''Aplodontia'', and family, Aplodontiidae. It should not be confused with true

North American North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Ca ...

and

Eurasian beaver The Eurasian beaver (''Castor fiber'') or European beaver is a beaver species that was once widespread in Eurasia, but was hunted to near-extinction for both its fur and castoreum. At the turn of the 20th century, only about 1,200 beavers survi ...

s, to which it is not closely related, being more closely related to

squirrels Squirrels are members of the family Sciuridae, a family that includes small or medium-size rodents. The squirrel family includes tree squirrels, ground squirrels (including chipmunks and prairie dogs, among others), and flying squirrels. Squ ...

. There are 7 subspecies of mountain beavers, 6 of which are found in

California California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the m ...

and 3 of which are endemic to the state.

Spelling and etymology

Most references use the spelling Aplodontidae for the family name. This has been deemed incorrect due to the technical rules of converting a genus name into a family name. The proper conversion of ''Aplodontia'' to a family name is to drop the -a only and add -. Thus, Aplodontiidae is technically correct. This spelling is gaining acceptance in modern texts and is the standard spelling currently recognized by the Integrated Taxonomic Information System. Alternate spellings of the genus name have also been reported, with as many as 30 variants historically. These include ''Haplodontia'', ''Haplodon'', ''Aploodontia'', ''Apluodontia'', and ''Aplodontie'', among others. The name ''Aplodontia'' ("simple tooth") is in reference to the single large basin comprising the bulk of each cheek tooth. The specific epithet, ''rufa'' means red or reddish.

Taxonomy and phylogeny

The mountain beaver is considered a

living fossil A living fossil is an extant taxon that cosmetically resembles related species known only from the fossil record. To be considered a living fossil, the fossil species must be old relative to the time of origin of the extant clade. Living foss ...

, due to the presence of a host of primitive characteristics, particularly the protrogomorphous zygomasseteric system. This condition is similar to what is found in most mammal groups, such as rabbits, where no extreme specialization of the

masseter muscle In human anatomy, the masseter is one of the muscles of mastication. Found only in mammals, it is particularly powerful in herbivores to facilitate chewing of plant matter. The most obvious muscle of mastication is the masseter muscle, since it ...

has evolved. In the protrogomorphous condition, the masseter muscle does not pass through the

infraorbital foramen In human anatomy, the infraorbital foramen is one of two small holes in the skull's upper jawbone (maxillary bone), located below the eye socket and to the left and right of the nose. Both holes are used for blood vessels and nerves. In anatomica ...

as it does in

guinea pig The guinea pig or domestic guinea pig (''Cavia porcellus''), also known as the cavy or domestic cavy (), is a species of rodent belonging to the genus '' Cavia'' in the family Caviidae. Breeders tend to use the word ''cavy'' to describe the ...

s and mice. Likewise, the medial masseter muscle attaches to the base of the

zygomatic arch In anatomy, the zygomatic arch, or cheek bone, is a part of the skull formed by the zygomatic process of the temporal bone (a bone extending forward from the side of the skull, over the opening of the ear) and the temporal process of the zygo ...

and does not extend to the region in front of the eye as is seen in squirrels and mice. The mountain beaver is the only living rodent with this primitive cranial and muscular feature (except perhaps the

blesmol The blesmols, also known as mole-rats, or African mole-rats, are burrowing rodents of the family Bathyergidae. They represent a distinct evolution of a subterranean life among rodents much like the pocket gophers of North America, the tuco-tu ...

s, which clearly evolved protrogomorphy from a hystricomorphous ancestor). The mountain beaver was once thought to be related to the earliest protrogomorphous rodents, such as the ischyromyids (''

Paramys ''Paramys'' is an extinct genus of rodents from North America, Europe, and Asia. It is one of the oldest genera of rodents known and probably lived in trees. While the genus name literally means "near a mouse A mouse ( : mice) is a smal ...

''). Both molecular and morphological phylogeneticists have recently suggested a more distant relationship to these animals. Molecular results have consistently produced a sister relationship between the mountain beaver and the squirrels (family Sciuridae). This clade is referred to as Sciuroidea, Sciuromorpha (not to be confused with the sciuromorphous zygomasseteric system), or Sciurida, depending on the author. According to the

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

record, the Aplodontioidea split from the squirrels in the Middle or Late

Eocene The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', " ...

as indicated by the extinct genera '' Spurimus'' and '' Prosciurus''. The fossil record for the genus ''Aplodontia'' extends only to the Late

Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was finally confirmed in ...

of North America.

Closest relatives

The mountain beaver is considered a

has evolved. In the protrogomorphous condition, the masseter muscle does not pass through the

as it does in

s and mice. Likewise, the medial masseter muscle attaches to the base of the

s, which clearly evolved protrogomorphy from a hystricomorphous ancestor). The mountain beaver was once thought to be related to the earliest protrogomorphous rodents, such as the ischyromyids (''

as indicated by the extinct genera '' Spurimus'' and '' Prosciurus''. The fossil record for the genus ''Aplodontia'' extends only to the Late

of North America.

Subspecies

At present, seven subspecies of ''Aplodontia rufa'' are recognized: *''A. r. californica'' (Peters, 1864): distributed throughout the Sierra Nevada in Northern California and extreme western

Nevada Nevada ( ; ) is a state in the Western region of the United States. It is bordered by Oregon to the northwest, Idaho to the northeast, California to the west, Arizona to the southeast, and Utah to the east. Nevada is the 7th-most extensive, ...

*''A. r. humboldtiana'' Taylor, 1916: restricted to the far northwestern coast of

*''A. r. nigra'' Taylor, 1914: restricted to a small region in southern

Mendocino County, California Mendocino County (; ''Mendocino'', Spanish for "of Mendoza) is a county located on the North Coast of the U.S. state of California. As of the 2020 census, the population was 91,601. The county seat is Ukiah. Mendocino County consists whol ...

*''A. r. pacifica'' Merriam, 1899: distributed across coastal

Oregon Oregon () is a state in the Pacific Northwest region of the Western United States. The Columbia River delineates much of Oregon's northern boundary with Washington, while the Snake River delineates much of its eastern boundary with Idaho. T ...

*''A. r. phaea'' Merriam, 1899: found mostly in

Point Reyes Point Reyes (, meaning "Point of the Kings") is a prominent cape and popular Northern California tourist destination on the Pacific coast. Located in Marin County, it is approximately west-northwest of San Francisco. The term is often appli ...

, northwest of

San Francisco, California San Francisco (; Spanish for " Saint Francis"), officially the City and County of San Francisco, is the commercial, financial, and cultural center of Northern California. The city proper is the fourth most populous in California and 17th ...

*''A. r. rainieri'' Merriam, 1899: found across the Cascade Range from southern

British Columbia British Columbia (commonly abbreviated as BC) is the westernmost province of Canada, situated between the Pacific Ocean and the Rocky Mountains. It has a diverse geography, with rugged landscapes that include rocky coastlines, sandy beaches, ...

to northern California *''A. r. rufa'' (Rafinesque, 1817): found along coastal

Washington Washington commonly refers to: * Washington (state), United States * Washington, D.C., the capital of the United States ** A metonym for the federal government of the United States ** Washington metropolitan area, the metropolitan area centered o ...

, particularly on the

Olympic Peninsula The Olympic Peninsula is a large arm of land in western Washington that lies across Puget Sound from Seattle, and contains Olympic National Park. It is bounded on the west by the Pacific Ocean, the north by the Strait of Juan de Fuca, and th ...

Description

Mountain beavers are gray or brown, but their fur can range from slightly more reddish to more blackish depending on subspecies, with a light patch under each ear. The animals have distinctively short tails. Adults weigh about , with a few specimens topping . Total length is about , with a tail length of . Their superficial similarity with true beavers reflects only their relatively large size (for rodents), strong odor, preference for living in extremely watery / moist habitats, and propensity to consume tree seedlings as food. Mountain beavers do not fell adult trees (though such trees may be killed by "

girdling Girdling, also called ring-barking, is the complete removal of the bark (consisting of cork cambium or "phellogen", phloem, cambium and sometimes going into the xylem) from around the entire circumference of either a branch or trunk of a woody ...

"), build dams, live in lodges, or communicate by tail slappings. They are predominantly nocturnal in above ground activities. They are known to climb trees a few meters to acquire food in the form of branches and leaves, but otherwise their diet consists mostly of ferns, especially species that are toxic to other animals. The

skull The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, th ...

is protrogomorphous;Druzinsky, Robert E.
Functional anatomy of incisal biting in Aplodontia rufa and sciuromorph rodents–Part 1: masticatory muscles, skull shape and digging
" Cells Tissues Organs 191.6 (2010): 510-522. it has no specialized attachments for the

s as seen in other rodents. It is flattened and lacks a

postorbital process The postorbital process is a projection on the frontal bone near the rear upper edge of the eye socket. In many mammals, it reaches down to the zygomatic arch, forming the postorbital bar. References See also * Orbital process In the human ...

. The baculum is thin and distinctly forked. The

penis A penis (plural ''penises'' or ''penes'' () is the primary sexual organ that male animals use to inseminate females (or hermaphrodites) during copulation. Such organs occur in many animals, both vertebrate and invertebrate, but males d ...

is about in length. The male does not have a true

scrotum The scrotum or scrotal sac is an anatomical male reproductive structure located at the base of the penis that consists of a suspended dual-chambered sac of skin and smooth muscle. It is present in most terrestrial male mammals. The scrotum co ...

, but the

testes A testicle or testis (plural testes) is the male reproductive gland or gonad in all bilaterians, including humans. It is homologous to the female ovary. The functions of the testes are to produce both sperm and androgens, primarily testoste ...

move into a position called semiscrotal during the breeding season. Mountain beavers have an unusual projection on each molar and premolar tooth, which is unique among mammals and allows for easy identification of teeth. This projection points toward the cheek on the upper tooth row, but points toward the tongue on the

lower Lower may refer to: *Lower (surname) *Lower Township, New Jersey *Lower Receiver (firearms) *Lower Wick Gloucestershire, England See also *Nizhny Nizhny (russian: Ни́жний; masculine), Nizhnyaya (; feminine), or Nizhneye (russian: Ни́� ...

. The cheek teeth lack the complex folds of other rodents and instead consist of single basins. They are

hypsodont Hypsodont is a pattern of dentition with high-crowned teeth and enamel extending past the gum line, providing extra material for wear and tear. Some examples of animals with hypsodont dentition are cows and horses; all animals that feed on gritt ...

and ever-growing. Two upper and one lower premolars are present, along with all the molars, giving a

dental formula Dentition pertains to the development of teeth and their arrangement in the mouth. In particular, it is the characteristic arrangement, kind, and number of teeth in a given species at a given age. That is, the number, type, and morpho-physiolog ...

of citation needed Mountain beavers cannot produce concentrated urine. They are thought to be physiologically restricted to the temperate rain forest regions of the North American Pacific coast and moist microenvironments inland due to their inability to obtain sufficient water in more arid environments. It is thought that Aplodontia prefer vegetation high in water content due to their poor ability to concentrate urine which makes it necessary to consume large amounts of water daily.

Habitat and distribution

Mountain beavers are found in the

Cascade Mountains The Cascade Range or Cascades is a major mountain range of western North America, extending from southern British Columbia through Washington and Oregon to Northern California. It includes both non-volcanic mountains, such as the North Cascades, a ...

and southward including the rest of the Cascade Range in the United States, the

Olympic Mountains The Olympic Mountains are a mountain range on the Olympic Peninsula of the Pacific Northwest of the United States. The mountains, part of the Pacific Coast Ranges, are not especially high – Mount Olympus is the highest at ; however, the easte ...

and Coast Ranges of Washington and Oregon, plus the

Klamath Mountains The Klamath Mountains are a rugged and lightly populated mountain range in northwestern California and southwestern Oregon in the western United States. As a mountain system within both the greater Pacific Coast Ranges and the California Coast ...

, and the Sierra Nevada, Point Arena and Pt. Reyes of

and extreme western

."Mountain Beaver" in ''The New Encyclopedia of Mammals''. David MacDonald (ed). Oxford University Press, 2001. Pages 596–597. They range from sea level to the

tree line The tree line is the edge of the habitat at which trees are capable of growing. It is found at high elevations and high latitudes. Beyond the tree line, trees cannot tolerate the environmental conditions (usually cold temperatures, extreme snow ...

. They can be found in both

deciduous In the fields of horticulture and Botany, the term ''deciduous'' () means "falling off at maturity" and "tending to fall off", in reference to trees and shrubs that seasonally shed leaves, usually in the autumn; to the shedding of petals, ...

and coniferous forests, but throughout most of the range they appear to prefer the former.

Behavior

Mountain beavers are capable of climbing trees, but rarely travel far from burrows. Their thumbs are slightly

opposable The thumb is the first digit of the hand, next to the index finger. When a person is standing in the medical anatomical position (where the palm is facing to the front), the thumb is the outermost digit. The Medical Latin English noun for thumb ...

and the animals will sit on their hindquarters and manipulate food with their forelimbs and incisors. Mountain beavers are asocial and do not live in shared burrows. Burrows usually consist of a network of tunnels built in deep soil. The entrances to these burrows often contain clumps of wilted vegetation which the animal likely uses as a kind of food cache as well as a source of nesting material. Mountain beavers seldom travel more than a few meters from their burrow entrances, taking advantage of the protection such burrows offer from predators such as cougars and owls (though skunks and weasels that also occupy mountain beaver burrows and tunnels may take nestlings as food). They appear to build

hay Hay is grass, legumes, or other herbaceous plants that have been cut and dried to be stored for use as animal fodder, either for large grazing animals raised as livestock, such as cattle, horses, goats, and sheep, or for smaller domesticat ...

mounds at some burrow entrances, but whether this behavior is related to water regulation, curing food, or gathering nest materials is debated. Mountain beavers are partially nocturnal, spending more time active at night than the day but still active during both periods. They actively feed in periods of up to 2 hours and 45 minutes throughout the day with 6 or 7 periods of feeding per day. In total they forage for up to 9 hours per day. These animals are physiologically limited to moist microenvironments, with most subspecies occurring only in regions with minimal snowfall and cool winters. They do not appear to be able to conserve body heat or warmth as efficiently as other rodents, nor do they hibernate.

Diet

They exhibit

coprophagy Coprophagia () or coprophagy () is the consumption of feces. The word is derived from the grc, κόπρος , "feces" and , "to eat". Coprophagy refers to many kinds of feces-eating, including eating feces of other species (heterospecifics), o ...

and eat soft fecal pellets to obtain maximum nutrients; hard

fecal Feces ( or faeces), known colloquially and in slang as poo and poop, are the solid or semi-solid remains of food that was not digested in the small intestine, and has been broken down by bacteria in the large intestine. Feces contain a relati ...

pellets are transferred to fecal chambers located within the burrow system. Food includes fleshy herbs and young shoots of more woody plants.

Fern A fern (Polypodiopsida or Polypodiophyta ) is a member of a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers. The polypodiophytes include all living pteridophytes exce ...

s probably make up the bulk of their diets. They appear to be strictly

herbivorous A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpar ...

. Their consumption of seedling trees has led some to consider them as pests.

Ecology

Known predators include bobcats, coyotes, cougars,

golden eagle The golden eagle (''Aquila chrysaetos'') is a bird of prey living in the Northern Hemisphere. It is the most widely distributed species of eagle. Like all eagles, it belongs to the family Accipitridae. They are one of the best-known birds of ...

s, and

owl Owls are birds from the order Strigiformes (), which includes over 200 species of mostly solitary and nocturnal birds of prey typified by an upright stance, a large, broad head, binocular vision, binaural hearing, sharp talons, and feathers a ...

s. Among the parasites of the mountain beaver is the largest

flea Flea, the common name for the order Siphonaptera, includes 2,500 species of small flightless insects that live as external parasites of mammals and birds. Fleas live by ingesting the blood of their hosts. Adult fleas grow to about long, a ...

known, '' Hystrichopsylla schefferi''. Females of this flea can be long. Mountain beavers are considered pests in areas of the Pacific Northwest because of the extensive damage they cause to forest trees due to basal-grinding (removal of bark), branch cutting, or clipping small sapling and seedlings. This damage often poses a problem for forest management and reforestation when smaller seedlings are buried or uprooted during mountain beaver feeding and can result in tree deformities, growth suppression, and mortality. The

United States Forest Service The United States Forest Service (USFS) is an agency of the U.S. Department of Agriculture that administers the nation's 154 national forests and 20 national grasslands. The Forest Service manages of land. Major divisions of the agency in ...

has maintained a program to exterminate the mountain beaver due to beavers causing economic damage to commercial reforestation. Damage control measures taken to protect forest trees by controlling the mountain beaver population include trapping, placing toxic baits, and placing physical barriers (e.g. plastic mesh tubes) around the base of an individual tree.

Breeding

The breeding season is between January and March, with two or three young born February to April. The ovulation period lasts a few weeks and gestation lasts for a month. The young are born hairless, pink, and blind. They are weaned at 6 to 8 weeks and leave the burrow soon after. Lifespans are 5 to 10 years – fairly long for rodents. They are not social, though home ranges can overlap.

Status and conservation

The IUCN lists the mountain beaver as a species of

least concern A least-concern species is a species that has been categorized by the International Union for Conservation of Nature (IUCN) as evaluated as not being a focus of species conservation because the specific species is still plentiful in the wild. T ...

. However, one subspecies, the Point Arena mountain beaver (''A. r. nigra'') of California, is considered

endangered An endangered species is a species that is very likely to become extinct in the near future, either worldwide or in a particular political jurisdiction. Endangered species may be at risk due to factors such as habitat loss, poaching and in ...

by the

U.S. Fish and Wildlife Service The United States Fish and Wildlife Service (USFWS or FWS) is an agency within the United States Department of the Interior dedicated to the management of fish, wildlife, and natural habitats. The mission of the agency is "working with othe ...

, and ''Critically Imperiled'' by

NatureServe NatureServe, Inc. is a non-profit organization based in Arlington County, Virginia, US, that provides proprietary wildlife conservation-related data, tools, and services to private and government clients, partner organizations, and the public. Nat ...

. Originally listed in 1991, the Point Arena mountain beaver is distinguished by its black colouration and by characteristic body proportions, including a smaller overall size. The principal threat to this subspecies is habitat loss and fragmentation; its remaining range comprises a disjunct region of 24 square miles in western

Mendocino County Mendocino County (; ''Mendocino'', Spanish for "of Mendoza) is a county located on the North Coast of the U.S. state of California. As of the 2020 census, the population was 91,601. The county seat is Ukiah. Mendocino County consists whol ...

Notes

References

* Adkins, R. M. E. L. Gelke, D. Rowe, and R. L. Honeycutt. 2001.

Molecular phylogeny Molecular phylogenetics () is the branch of phylogeny that analyzes genetic, hereditary molecular differences, predominantly in DNA sequences, to gain information on an organism's evolutionary relationships. From these analyses, it is possible to ...

and divergence time estimates for major rodent groups: Evidence from multiple

gene In biology, the word gene (from , ; "... Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a b ...

s.'' Molecular Biology and Evolution'', 18:777–791. * McKenna, Malcolm C., and Bell, Susan K. 1997. ''Classification of Mammals Above the Species Level''. Columbia University Press, New York, 631 pp. * Nowak, R. M. 1999. ''Walker's Mammals of the World'', Vol. 2. Johns Hopkins University Press, London. *

External links

* {{Taxonbar, from=Q503813 Fauna of the Sierra Nevada (United States) Mammals of Canada Mammals of the United States Extant Pleistocene first appearances Rodents by common name Taxa named by Constantine Samuel Rafinesque Endemic fauna of the Pacific Northwest