Rodents (from Latin Rodere, “to gnaw”) are mammals of the order Rodentia, which are characterized by a single pair of continuously growing incisors in each of the upper and lower jaws. About 40% of all mammal species are rodents (2,277 species); they are found in vast numbers on all continents except Antarctica. They are the most diversified mammalian order and live in a variety of terrestrial habitats, including human-made environments.
Species can be arboreal, fossorial (burrowing), or semiaquatic. Well-known rodents include mice, rats, squirrels, prairie dogs, chipmunks, chinchillas, porcupines, beavers, guinea pigs, hamsters, gerbils and capybaras. Rabbits, hares, and pikas, whose incisors also grow continually, were once included with them, but are now considered to be in a separate order, the Lagomorpha. Nonetheless, Rodentia and Lagomorpha are sister groups, sharing a most recent common ancestor and forming the clade of Glires.