Rodent

The order Rodentia has been the most spectacularly successful of all the branches on the mammal family tree. Currently there are, depending on the authority consulted, between 2000 and 3000 species of rodent—roughly half of all mammal species. Rodents are found in vast numbers on all continents (they are the only placental order other than the bats to reach Australia without human introduction), most islands, and in all habitats bar the oceans.

Most rodents are small. The tiny African Pygmy Mouse is only 6 cm in length and 7 grams in weight. On the other hand, the Capybara can weigh up to 45 kg (100 pounds) and the extinct Phoberomys pattersoni is believed to have weighed 700 kg.

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 the origin of the name, from the 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, seeds in particular, but there are a few exceptions which eat insects or even fish.

Classification

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

• ORDER RODENTIA

• Suborder Sciurognathi
  • Superfamily Sciurida
    • Family Sciuridae: squirrels, including chipmunks & prairie dogs
  • Superfamily Castorimorpha
    • Family Castoridae: beavers
  • Superfamily Anomaluromorpha
    • Family Anomaluridae: scaly-tailed squirrels
    • Family Pedetidae: springhares
  • Superfamily Ctenodactylomorpha
    • Family Ctenodactylidae: gundis
  • Superfamily Glirimorpha
    • Family Gliridae: dormice
  • Superfamily Myomorpha
    • Family Geomyidae: pocket gophers
    • Family Heteromyidae: kangaroo mice
    • Family Zapodidae: jumping mice
    • Family Dipodidae: jerboas
    • Family Cricetidae: cricetid mice, including hamsters
    • Family Gerbillidae: gerbils
    • Family Muridae: true mice, including true rats
    • Family Rhizomyidae: bamboo rats
    • Family Spalacidae: mole rats

• Suborder Hystricognathi
  • Superfamily Hystricomorpha
    • Family Hystricidae: Old World porcupines
    • Family Erethizontidae: New World porcupines
    • Family Thryonomyidae: cane rats
  • Superfamily Bathyergomorpha
    • Family Bathyergidae: African mole rats
  • Superfamily Caviomorpha
    • Family Octodontidae: octodonts
    • Family Echimyidae: spiny rats, including nutrias
    • Family Capromyidae: hutias
    • Family Dasyproctidae: agoutis
    • Family Dinomyidae: pacaranas
    • Family Caviidae: cavies, including guinea pigs
    • Family Hydrochoeridae: Capybara
    • Family Chinchillidae: chinchillas and viscachas
    • Family Abrocomidae: chinchilla rats

Recent work has suggested that the rodents may actually be biologically polyphyletic (i.e. have evolved more than once), specifically the Myomorpha may constitute a distinct and separate lineage, in which case the order would have to be revised.