The order Rodentia, with 28 families including ~2,020 living species, is the largest order of mammals. They are found worldwide except in Antarctica and on some oceanic islands. Ecologically, they are remarkably diverse; species have adapted to environments ranging from rainforests to deserts. Many rodents are to some degree omnivorous; others are highly specialized, eating, for example, only a few species of invertebrates or fungi.

Despite their morphologic and ecologic diversity, all rodents share one characteristic: a highly specialized dentition for gnawing. Rodents have a single pair of upper and lower incisors. Between each incisor and the first cheek tooth is a toothless interval called the diastema. The incisors are rootless and grow continuously. Enamel is deposited on the anterior and lateral incisor surfaces; the posterior incisor surface is dentin. During gnawing, as the incisors chisel against each other, they wear away the softer dentine, leaving a sharp enamel edge. This “self-sharpening” system is very effective and is one of the keys to the success of rodents.

Despite the large number of rodents, few species are owned as pets. The common pet rodents are chinchillas, gerbils, guinea pigs, hamsters, mice, and rats. Hamsters, gerbils, mice, and rats belong to the family Muridae in the rodent suborder, Sciurognathi. Chinchillas and guinea pigs are placed in the other rodent suborder, Hystricognathi. Less common pet rodents are African giant pouched rats, degus, prairie dogs, spiny mice, and voles.

Last full review/revision July 2011 by Thomas M. Donnelly, BVSc, DACLAM