The order Rodentia is comprised of over 2,000 species, which are subdivided into many families. The Capromyidae, Castoridae, Cricetidae, Erethizontidae, Muridae, Sciuridae and Dipodidae are some of the most common families.
The family Muridae is the largest, containing nearly two-thirds of all rodent species. This family includes several subfamilies and includes sand rats, gerbils, crested rats and old world rats and mice.
The family Cricetidae is the second largest, numbering approximately 600 species in total. This family encompasses most mouse-like hamsters, such as voles and lemmings.
The family Sciruridae includes over 200 species. However, species belonging to this family are some of the most commonly recognized rodents. Squirrels, chipmunks, marmots and woodchucks belong to this family, as does the flying squirrel.