Rodentia is an order of mammals also known as rodents, characterised by a single pair of continuously growing incisors in each of the upper and lower jaws which must be kept short by gnawing.
Forty percent of mammal species are rodents, and they are found in vast numbers on all continents other than Antarctica. Common rodents include mice, rats, squirrels, porcupines, beavers, guinea pigs, and hamsters. Rodents have sharp incisors they use to gnaw wood, break into food, and bite predators. Most rodents eat seeds or plants, though some have more varied diets. Some species have historically been pests, eating seeds stored by people and spreading disease.
Many rodents are small; the tiny African pygmy mouse, Mus minutoides, can be as small as 6 cm (2.4 in) in length and 7 g (0.25 oz) in weight at maturity, and the Baluchistan pygmy jerboa, Salpingotulus michaelis, is of roughly similar or slightly smaller dimensions. On the other hand, the largest extant rodent, the capybara, Hydrochoerus hydrochaeris, usually weighs up to 65 kg (140 lb), with exceptional specimens weighing up to 91 kg (200 lb). Several enormous rodents are known from the fossil record, the largest known being Josephoartigasia monesi, which is estimated to have typically weighed about 1,000 kg (2,200 lb), and possibly up to 1,534 kg (3,380 lb) or 2,586 kg (5,700 lb) in large individuals.