The largest family of mammals are the rodents. These mammals are named rodent, which means "gnawing animal," because of their large incisor teeth and the way they eat. The two long pairs of incisors are used like chisels to gnaw on hard foods like nuts and wood. These incisors must grow continuously since they are worn down by gnawing.

There are 3 major types of rodents, represented by squirrels, mice and porcupines.

Squirrel-like rodents such as the squirrel and gopher, have bushy long tails and large eyes. They can live in trees or underground in tunnels. They may hibernate during the winter.
Mouse-like rodents include the mouse, rat and hamster. Some have a long, thin tail with short legs. Others have a short tail. They mostly live above ground, although some burrow under ground. They may also hibernate during the winter. Rats and mice often live near humans, sometimes in their buildings, so they can live off human food and garbage.
Porcupines differ from other mammals because they have long, sharp quills on their backs for protection.