Mice have bones because they are mammals, which means that they are vertebrates or animals with backbones and skeletal systems. Mice belong to the largest order of mammals, rodentia or rodents, which includes rats, guinea pigs, prairie dogs, squirrels, beavers and porcupines.
Rodents are characterized by incisors, or sharp teeth, on their lower and upper jaws. The incisors of rodents grow continually, and the dentine on the incisors must wear away through gnawing so that the incisors do not grow so long that they pierce the skull. Mice are members of a taxonomic hierarchy of rodents called mouse-like rodents, or myomorpha. This group includes house mice, dormice, pocket mice, jumping mice, rats and pocket gophers. Mouse-like rodents have special jaw and molar structures that give them powerful gnawing capabilities. Mouse-like rodents are further divided into taxonomic groups, of which mice are members of the group called muridae, which also includes rats, lemmings, voles, hamsters and gerbils.
Mice are small mammals with slender bodies, tapered muzzles, noticeable ears, sharp claws and long tails. The smallest species, the pygmy mouse, weighs from one-tenth to one-half of an ounce, while the largest, the flat-haired mouse of India, weighs just over one-half of an ounce. Fur texture varies from short and soft to long and spiny. Colors may be white, gray, brown, reddish brown, black or a combination of these.