Family of the Week: The Beavers

The Metazoic family Castoridae is basically a continuation of the family we have today. The beaver is one of the largest rodents we have today. The modern basic body form is round, humpbacked, small head and eyes and a short muzzle. It's most noticable features are the short, flat tail and large incisors. During the Metazoic, the family branches out, and takes on several forms. Not only the familiar animal I just described, but there are also forms that resembles rats, squirrels and even guinea pigs. Most species have either short tails or no tails. The longest tails belong to Trogonomys, which are tree-dwelling, rat-like creatures. In most species, the tails are naked, scaly, in some they are covered in fine fur. The feet are naked and webbed in all but Trogonomys. The head is still short and the incisors are long, sharp and powerful. The ears are either very small, or absent in most species. The fur is slick and oily, the claws are long and sharp. The legs are generally short, or in some cases have turned to flippers. The body has become elongate in some forms, with the hind feet being fused with the tail to form a large flipper in the back, which is paddled in an up and down motion for swimming. The ears and nostrils are capable of closing while underwater and the eyes have a special nictitating membrane that closes over the eyes while they are underwater.

The largest member of the family is in the genus Phocapotamus. This animal closely resembles a hippopotamus with flippers instead of legs. The head of this animal is very large and blunt. They cannot walk very well on land. They live alone or in couples. There is no tail in this animal, and they are covered with very short, slick fur. The smallest member of this family is in the genus Castorella. These are small replicas of modern beavers. Like modern beavers, the species in this family also build nests, or dams. Trogonomys lives in trees and builds a nest among the branches to house it's young. The nest is usually constructed of twigs and leaves. Other species cut up saplings, as they do today and build their dams in running water. Most species live singly or in couples. Though in the genus Caprymnus, they tend to live in the largest groups of all Castorids. Caprymnus somewhat resembles a large guinea pig, or the capybara.

Contrary to popular belief, no species of this family eats fish. They are all strictly vegetarians. Their diet consists of aquatic plants, flowers, leaves, grass, and fungi. Though a large species like Caprymnus is safer in large groups, they do tend to fall prey to some predators. Foxes, barofelids and mongooses are their major enemies. They can defend themselves by swimming, or if they are cornered, they can use their sharp claws and teeth for defense.