Rodentia

Rodentia is the largest order of mammals, comprising more than 2,000 living species of rodents. Members range from mice, rats, and squirrels to beavers, porcupines, guinea pigs, hamsters, and capybaras. They occur in a broad range of habitats across much of the world, from forests and grasslands to deserts and urban areas.

Key defining feature is dental: the two continuously growing incisors in each jaw, separated from the cheek teeth by a large diastema; canines are absent. The incisors are chisel-shaped and grow throughout life, with enamel on the front surface creating a self-sharpening edge.

Rodentia is divided into several suborders, including Myomorpha (mice and rats), Sciuromorpha (squirrels and relatives), Castorimorpha (beavers and their kin), Hystricomorpha (guinea pigs, capybaras, chinchillas, porcupines), and Anomaluromorpha (springhares and related species).

Ecology and life history vary widely. Many species are herbivorous or omnivorous, with small-bodied rodents often feeding on seeds and invertebrates, while larger species may be more omnivorous or herbivorous. Reproduction is generally rapid, with large litter sizes and short generation times, contributing to high population turnover in favorable conditions.

Fossil evidence places rodents in the Paleocene, about 60 to 66 million years ago, with rapid diversification during the Cenozoic. They play important ecological roles as seed dispersers, prey items, and ecosystem engineers in some cases, notably beavers that build dams and alter habitats. Humans interact with rodents as pests, pet animals, and important model organisms in biomedical research.