The North American and Eurasian beavers are the only extant members of the family Castoridae, contained within the genus, Castor.
Genetic research has shown the modern European and North American beaver populations to be distinct species and that hybridization is unlikely.
Although superficially similar to each other, there are several important differences between the two species.
Eurasian beavers tend to be slightly larger, with larger, less rounded heads, longer, narrower muzzles, thinner, shorter and lighter underfur, narrower, less oval-shaped tails and shorter shin bones, making them less capable of bipedal locomotion than the North American species.
Eurasian beavers have longer nasal bones than their North American cousins, with the widest point being at the end of the snout for the former, and in the middle for the latter.
The nasal opening for the Eurasian species is triangular, unlike that of the North American, which is square.
The foramen magnum is rounded in the Eurasian beaver and triangular in the North American.
The anal glands of the Eurasian beaver are larger and thin-walled with a large internal volume compared to that of the North American species.
The guard hairs of the Eurasian beaver have a longer hollow medulla at their tips.
Fur colour is also different.
Overall, 66% of Eurasian beavers have pale brown or beige fur, 20% have reddish brown, nearly 8% are brown and only 4% have blackish coats.
In North American beavers, 50% have pale brown fur, 25% are reddish brown, 20% are brown and 6% are blackish.

The two species are not genetically compatible.
North American beavers have 40 chromosomes, while Eurasian beavers have 48.
More than 27 attempts were made in Russia to hybridize the two species, with one breeding between a male North American beaver and a female European resulting in a single stillborn kit.
These factors make interspecific breeding unlikely in areas where the two species' ranges overlap.
The North American and Eurasian beavers are the only extant members of the family Castoridae, contained within the genus, Castor. Genetic research has shown the modern European and North American beaver populations to be distinct species and that hybridization is unlikely. Although superficially similar to each other, there are several important differences between the two species. Eurasian beavers tend to be slightly larger, with larger, less rounded heads, longer, narrower muzzles, thinner, shorter and lighter underfur, narrower, less oval-shaped tails and shorter shin bones, making them less capable of bipedal locomotion than the North American species. Eurasian beavers have longer nasal bones than their North American cousins, with the widest point being at the end of the snout for the former, and in the middle for the latter. The nasal opening for the Eurasian species is triangular, unlike that of the North American, which is square. The foramen magnum is rounded in the Eurasian beaver and triangular in the North American. The anal glands of the Eurasian beaver are larger and thin-walled with a large internal volume compared to that of the North American species. The guard hairs of the Eurasian beaver have a longer hollow medulla at their tips. Fur colour is also different. Overall, 66% of Eurasian beavers have pale brown or beige fur, 20% have reddish brown, nearly 8% are brown and only 4% have blackish coats. In North American beavers, 50% have pale brown fur, 25% are reddish brown, 20% are brown and 6% are blackish.
The two species are not genetically compatible. North American beavers have 40 chromosomes, while Eurasian beavers have 48. More than 27 attempts were made in Russia to hybridize the two species, with one breeding between a male North American beaver and a female European resulting in a single stillborn kit. These factors make interspecific breeding unlikely in areas where the two species' ranges overlap.
Beaver