After their first year, the young help their parents repair dams and lodges; older siblings may also help raise newly born offspring.

[2] Cognates of beaver is the source for several European placenames, including those of Beverley, Bièvres, Biberbach, Biebrich, Bibra, Bibern, Bibrka, Bobr, Bober, Bóbrka, Bjurholm, Bjurälven, and Bjurum.

The Eurasian beaver is slightly longer and has a more lengthened skull, triangular nasal cavities (as opposed to the square ones of the North American species), a lighter fur color, and a narrower tail.

They originated in North America in the late Eocene and colonized Eurasia via the Bering Land Bridge in the early Oligocene, coinciding with the Grande Coupure, a time of significant changes in animal species around 33 million years ago (myr).

[14][15] The more basal castorids had several unique features: more complex occlusion between cheek teeth, parallel rows of upper teeth, premolars that were only slightly smaller than molars, the presence of a third set of premolars (P3), a hole in the stapes of the inner ear, a smooth palatine bone (with the palatine opening closer to the rear end of the bone), and a longer snout.

This group consisted primarily of smaller animals with relatively large front legs, a flattened skull, and a reduced tail—all features of a fossorial (burrowing) lifestyle.

Members of the subfamily Castoroidinae are considered to be a sister group to modern beavers, and included giants like Castoroides of North America and Trogontherium of Eurasia.

A beaver's lips can close behind the incisors, preventing water from entering their mouths as they cut and bite onto things while submerged.

The tail has multiple functions: it provides support for the animal when it is upright (such as when chewing down a tree), acts as a rudder when it is swimming, and stores fat for winter.

Anal secretions are darker in females than males among Eurasian beavers, while the reverse is true for the North American species.

[39] When diving, their heart rate decreases to 60 beats per minute, half its normal pace, and blood flow is directed more towards the brain.

Beavers have increasingly settled at or near human-made environments, including agricultural areas, suburbs, golf courses, and shopping malls.

During the fall and winter, they eat more bark and cambium of woody plants; tree and shrub species consumed include aspen, birch, oak, dogwood, willow and alder.

[55] Beavers need trees and shrubs to use as building material for dams, which restrict flowing water to create a pond for them to live in, and for lodges, which act as shelters and refuges from predators and the elements.

[24][60] The above-water space inside the lodge is known as the "living chamber", and a "dining area" may exist close to the water entrance.

The canals fill with groundwater and give beavers access and easier transport of resources, as well as allow them to escape predators.

[64] One study in the Adirondacks found that beaver engineering lead to an increase of more than 33 percent in herbaceous plant diversity along the water's edge.

Damming typically leads to an increase of slow or motionless water species, like dragonflies, oligochaetes, snails, and mussels.

The widening of the riparian zone associated with beaver dams has been shown to increase the abundance and diversity of birds favoring the water's edge, an impact that may be especially important in semi-arid climates.

[89] As trees are drowned by rising beaver impoundments, they become an ideal habitat for woodpeckers, which carve cavities that may be later used by other bird species.

[64] Beaver modifications to streams in Poland create habitats favorable to bat species that forage at the water surface and "prefer moderate vegetation clutter".

[90] Large herbivores, such as some deer species, benefit from beaver activity as they can access vegetation from fallen trees and ponds.

Kits suckle for as long as three months, but can eat solid food within their second week and rely on their parents and older siblings to bring it to them.

Beavers can damage crops, timber stocks, roads, ditches, gardens, and pastures via gnawing, eating, digging, and flooding.

[121][122] Beavers have historically been hunted and captured using deadfalls, snares, nets, bows and arrows, spears, clubs, firearms, and leg-hold traps.

[123][124] Castoreum was used for a variety of medical purposes; Pliny the Elder promoted it as a treatment for stomach problems, flatulence, seizures, sciatica, vertigo, and epilepsy.

[125] Castoreum's properties have been credited to the accumulation of salicylic acid from willow and aspen trees in the beaver's diet, and has a physiological effect comparable to aspirin.

Beaver tails were thus highly prized in Europe; they were described by French naturalist Pierre Belon as tasting like a "nicely dressed eel".

[130] In the late 16th century, Europeans began to deal in North American furs due to the lack of taxes or tariffs on the continent and the decline of fur-bearers at home.

French cartographer Nicolas de Fer illustrated beavers building a dam at Niagara Falls, fantastically depicting them like human builders.