Beavers are large, semi-aquatic rodents of the genus Castor, native to the temperate northern hemisphere. There are two species: the North American beaver (Castor canadensis) and the Eurasian beaver (C. fiber). Beavers are the second largest live rodent by capybara. They have strong bodies, with large heads, long incisors, resembling a chisel, brown or gray fur, arms-like forelegs, tangled hind legs, and flat, scaly tails. The Eurasian beaver has a longer skull, with a more triangular opening in the nasal bone, a lighter color of the layer, and a narrower tail. Animals can be found in several freshwater habitats, such as rivers, streams, lakes, and ponds. They are herbivores, eat bark, aquatic plants, herbs, and sedges.

Beavers build dams and huts using tree branches, vegetation, rocks, and mud; chew trees for building material. Dams hold water, and huts serve as shelters. Their infrastructure creates wetlands used by many other species, and due to their effect on other organisms in the ecosystem, they are considered a key species. Adult males and females live in monogamous couples with their descendants. When they are old enough, young people will help their parents repair dams and huts and help raise newborn offspring. Beavers own territories and mark them with the help of the aromatic aromas of mud, debris, and castoreum, a substance based on urine excreted through the beaver’s castor sacs. Beavers can also recognize their relatives by the secretions of their anal glands and are more likely to tolerate them as neighbors.

Historically, beavers were hunted for their fur, meat, and castoreum. Castoreum is used in medicine, perfumes, and food flavors, while beaver skins are an essential factor in the skin trade. Before defenses began in the 19th and early 20th centuries, persecution nearly wiped out both species. Their populations have rebounded, and both are listed as least disturbing by the IUCN Red List of mammals. In human culture, the beaver symbolizes hard work and is the national animal of Canada.

Etymology

The English word “beaver” comes from the Old English word beofor or befor (formerly written as bebr) and is related to the German word Biber and the Dutch word bever. The final origin of the word is from the Indo-European root for “brown.” The name of the genus Castor comes from the Greek kastor and translates as “beaver.”

Evolution

Beavers belong to rodentimorpha rodents, along with Heteromyidae (kangaroo rats, kangaroo mice, pocket mice, and spiny pocket mice) and gophers. Modern beavers are the only members of the Castoridae family. They appeared in North America in the late Eocene. They spread to Eurasia through the Bering Bridge during the early Oligocene, coinciding with the Grande Coupure, a period of sizeable faunal turnover about 33 million years ago (mya).

The more basal castorids have characteristics such as more complex occlusion between the cheek teeth, parallel upper dentitions, premolars close to the molars in size, the presence of the third set of premolars (P3), stiff muscles, smooth palate with a palatine foramen (opening). Near the back end of the bone and the elongated snout.

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