At least half of all species of mammals belong to order Rodentia -- the rodents -- according to the "National Audubon Society Field Guide to Mammals." Rodents have different features that allow their placement in various families. These different types of rodents do share similarities. They have bulbous eyes, a pair of incisors on the top and bottom jaw without any canine teeth, and most rodents have four toes on the front feet and five on the back.
The mountain beaver (Aplodontia rufa) is the sole representative of a type of rodent classified in the family Aplodontidae. The rodent's name is confusing, since it resembles a woodchuck and not a common beaver. Mountain beavers live in burrows dug underground and have a stout body and short tail. Mountain beavers live from central parts of California north through British Columbia, according to the New Hampshire Public Television Knowledge Network. The rodent has a diet consisting of ferns, grass and bark. Its chewing of bark and twigs probably led to its misleading name.
The squirrel family (Sciuridae) contains the tree and ground squirrels, flying squirrels, prairie dogs, woodchucks, marmots and chipmunks. Characterised by relative small sizes and silky fur, the rodents of this family often have bushy tails. These rodents usually have back legs longer than their front. The squirrel family has members in nearly every habitat throughout North America, with their absence felt only in the coldest polar regions and the hottest, most arid deserts. Species such as the southern flying squirrel and grey squirrel live in trees, while those like the prairie dog and others live in burrows underground.
A solid build, small eyes and ears, a shortened tail and large claws on the front feet are traits of the pocket gophers, a family of rodents classified as Geomyidae. Pocket gopher species, including the northern pocket gopher, western pocket gopher and plains pocket gopher, all dig elaborate burrows and tunnels in the earth. These rodents feed upon plants, which they most often access from underground. Pocket gophers take their name from the pouches in their cheeks. They store food and bedding in these specialised pouches, which they can turn inside out to release their contents.
In North America, only one member of the rodent family known as Erethizonditae occurs -- the common porcupine (Erethizon dorsatum). The porcupine is a rodent that ranges across the majority of Alaska, Canada, the western United States and parts of the Northeast. Able to climb trees with proficiency, the porcupine lives in many kinds of forests, including coniferous ones. Porcupines eat leaves, twigs, bark and an assortment of green plants. They are mostly active at night. Porcupines have as many as 30,000 sharp quills on their bodies, used for defence. The quills easily detach when a predator strikes at the rodent, leaving the attacker in pain as the porcupine escapes.