Rodent

Rodent, any mammal characterized by a pair of broad, sharp-edged, chisel-like incisor teeth that are firmly inserted in both jaws and are used in gnawing vegetation. The front surface of each incisor tooth is composed of enamel, and the hind surface is of soft dentine, which wears away during the process of gnawing so that the teeth are constantly kept sharp. Rodents have no canine teeth; a gap is present between the incisors and the grinding teeth, or molars. Most rodents are also characterized by well-developed ears.

There are more species of rodents than of any other mammalian order; more than 400 genera and about 2,000 species are widely distributed throughout the world. The largest of the rodents is the capybara; most other species are relatively small. Some rodents produce many litters of young each year. They dwell in various habitats: Some species are aquatic, some are terrestrial, and some live in burrows in the ground. Others are arboreal, and about 35 species are flying squirrels that are semiaerial, gliding from one tree to another.

Many rodents are economically injurious, destroying crops and stored foods. Rodents such as the house mouse and the Norway and black rats sometimes carry disease. Some species, such as the muskrat and beaver, are valued for their fur; dams built by beavers help to prevent erosion. Albino strains of the mouse and rat are important in biological experimentation. The white mouse, the gerbil, and the guinea pig are popular house pets.

Scientists continue to find new kinds of rodents. An unusual squirrel-like rodent called a Laotian rock rat, whose discovery in Laos was reported in 2005, belongs to a family of rodents thought to be extinct for 11 million years. The rodents had previously been known only from the fossil record.

Scientific classification: Rodents make up the order Rodentia.