Rodent

Rodents (Rodentia) are placental mammals. They contain 2,000-3000 species depending on the source, i.e. half of all recent mammal species. Rodents live on all continents and in all habitats, with the exception of the sea.

Most rodents are small. The tiny African pygmy mouse is only 6 cm in length (without the tail) and 7 g in weight. On the other hand, the capybara can weigh up to 45 kg (100 pounds).

Rodents have two incisors[?] in the upper as well as in the lower jaw which grow continuously and must be kept worn down by gnawing; this is where they get their name, from Latin rodere, to gnaw. These teeth are used for cutting wood, biting through the skin of fruit, or for defence. Nearly all rodents feed on plants, but there are a few exceptions which eat insects or even fish.

Classification

The order Rodentia may be divided in suborders, superfamilies and families. This is a common classification scheme:

• Suborder Sciurognathi
  • Superfamily Sciurida
    • Family Sciuridae (squirrels, including chipmunks, prairie dogs)
  • Superfamily Castorimorpha
    • Family Castoridae (beavers)
  • Superfamily Anomaluromorpha
    1. Family Anomaluridae (scaly-tailed squirrels[?])
    2. Family Pedetidae (springhares[?])
  • Superfamily Ctenodactylomorpha
    • Family Ctenodactylidae (gundis[?])
  • Superfamily Glirimorpha
    • Family Gliridae (dormice[?])
  • Superfamily Myomorpha
    1. Family Geomyidae (pocket gophers[?])
    2. Family Heteromyidae (kangaroo mice[?])
    3. Family Zapodidae (jumping mice[?])
    4. Family Dipodidae (jerboas)
    5. Family Cricetidae (cricetid mice[?], including hamsters)
    6. Family Gerbillidae (gerbils)
    7. Family Muridae (true mice, including true rats)
    8. Family Rhizomyidae (bamboo rats[?])
    9. Family Spalacidae (mole rats[?])
• Suborder Hystricognathi
  • Superfamily Hystricomorpha
    1. Family Hystricidae (Old World porcupines)
    2. Family Erethizontidae (New World porcupines)
    3. Family Thryonomyidae (cane rats[?])
  • Superfamily Bathyergomorpha
    • Family Bathyergidae (African mole rats[?])
  • Superfamily Caviomorpha
    1. Family Octodontidae (octodonts[?])
    2. Family Echimyidae (spiny rats[?], including nutrias[?])
    3. Family Capromyidae (hutias[?])
    4. Family Agoutidae (agoutis)
    5. Family Dinomyidae (pacaranas[?])
    6. Family Caviidae (cavies, including guinea pigs)
    7. Family Hydrochoeridae (capybaras)
    8. Family Chinchillidae (chinchillas)
    9. Family Abrocomidae (chinchilla rats[?])

Recent work has suggested that the rodents may actually be biologically polyphyletic (i.e. have evolved more than once), in which case the group would have to be split up.