Rodents

Rodentia is an order of mammals also known as rodents, characterised by two continuously-growing incisors in 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, chipmunks, gophers, porcupines, beavers, hamsters, gerbils, guinea pigs, degus, chinchillas, prairie dogs, and groundhogs. Rodents have sharp incisors that they use to gnaw wood, break into food, and bite predators. Most eat seeds or plants, though some have more varied diets. Some species have historically been pests, eating stored human seeds and spreading disease.
Many rodents are small; the tiny African pygmy mouse can be only 6 cm (2.4 in) in length and 7 g in weight at maturity, and the Baluchistan Pygmy Jerboa is of roughly similar or slightly smaller dimensions. On the other hand, the capybara can weigh up to 80 kg (, and the largest known rodent, the extinct Josephoartigasia monesi, is estimated to weigh about 1,000 kg, and possibly up to 1,534 kg or 2,586 kg.
Rodents have two incisors in the upper as well as in the lower jaw which grow continuously and must be kept worn down by gnawing; this is the origin of the name, from the Latin rodere, to gnaw, and dens, dentis, tooth. These teeth are used for cutting wood, biting through the skin of fruit, or for defense. The teeth have enamel on the outside and exposed dentine on the inside, so they self-sharpen during gnawing. Rodents lack canines, and have a space between their incisors and premolars. Nearly all rodents feed on plants, seeds in particular, but there are a few exceptions which eat insects or fish. Some squirrels are known to eat passerine birds like cardinals and blue jays.
Typical rodent tooth system
Rodents are important in many ecosystems because they reproduce rapidly, and can function as food sources for predators, mechanisms for seed dispersal, and as disease vectors. Humans use rodents as a source of fur, as pets, as model organisms in animal testing, for food, and even for detecting landmines.
Members of non-rodent orders such as Chiroptera (bats), Scandentia (treeshrews), Insectivora (moles, shrews and hedgehogs), Lagomorphs (hares, rabbits and pikas) and mustelid carnivores such as weasels and mink are sometimes confused with rodents.