Rodent

Rodents Fossil range: Late Paleocene - Recent
White-tailed Antelope Squirrel, Ammospermophilus leucurus
Scientific classification
Kingdom: Animalia Phylum: Chordata Class: Mammalia Subclass: Eutheria (unranked) Euarchontoglires Superorder: Glires Order: Rodentia Bowdich, 1821
Suborders
Sciuromorpha Castorimorpha Myomorpha Anomaluromorpha Hystricomorpha

Rodents are members of the order Rodentia, which is the largest order of mammals. Rodents are most distinguished by their teeth — the word "rodent" comes from the Latin word "rodere", meaning "to gnaw."

There are about 1500 species of rodents (Nowak 1983, UCMP 2007), including mice, rats, squirrels, and beavers. They are found on all continents except Antartica and in almost all land habitats from tropical forests to deserts to mountains and tundras. Some species live almost all their lives in trees and some under the ground.

Rodent characteristics

The incisor teeth of rodents are their most distinctive feature. An rodent's incisors grow continuously thoughout its life and must be kept worn down by gnawing. The incisors of a pocket gopher can grow 20 inches in one year. The incisors have enamel on the outside and exposed dentine on the inside, so they self-sharpen during gnawing. Rodents lack canines and first premolars, which creates a space between their incisors and their grinding teeth.

Most rodents are small; the tiny African pygmy mouse is one of the smallest rodents and is only 6 cm (2.5 inches) long and weighs 7 grams (.25 oz). The largest living rodent, the capybara can weigh up to 45 kg (100 pounds) and the extinct Phoberomys pattersoni is believed to have weighed up to 700 kg (1500 lbs).

Most rodents mature quickly and soon have offspring. A female meadow mouse (Microyus pennsyvanicus) can have up to 17 litters of 4 to 13 young in a year. Many rodents have an average life span of only a year or less, although some larger rodents such as beavers and porcupines can live over 20 years. The oldest recorded rodent was a Sumatran crested porcupine (Hystrix brachyura) which lived 27 years and 3 months (Voelker 1986).

Rodents in nature

Most rodents eat plants, including seeds, fruit, grasses and leaves, and the bark of trees. Some rodents prey on insects and other small animals. The fish eating rats (Ichthyomys) of South America and some others swim in streams to catch small fish.

Some squirrels help maintain and spread forests by burying the seeds of trees. Gophers and other burrowing rodents enrich the soil by mixing it and by burying vegetation. Beavers, by their dam building, help control flooding and create pond and meadow habitats which benefit many other species.

Rodents are an important source of food for many other animals, including birds, reptiles, and other mammals.

Rodents and humans

From earliest times rodents have been eaten by humans. Although the flesh of all species is edible, they are not an important food source in the world today. Exceptions are the capybara and the cavies, or guinea pigs, of South America which are both hunted and raised for meat and the bandicoot rat of Southeast Asia. The dormouse (Glis glis) was considered a delicacy in ancient Rome and is still eaten in parts of Europe today. In North America squirrels, groundhogs, muskrats, and porcupines are sometimes eaten.

Size and range of order

In terms of number of species — although not necessarily in terms of number of organisms (population) or biomass — rodents make up the largest order of mammals, with over 40 percent of mammalian species belonging to the order. Their success is probably due to their small size, short breeding cycle, and ability to gnaw and eat a wide variety of foods.(Lambert, 2000)

Characteristics

Capybara, the largest living rodent

Rodents are important in many ecosystems because they reproduce rapidly, and can function as food sources for predators, mechanisms for seed dispersal, and as disease vectors. Humans use rodents as a source of fur, as model organisms in animal testing, for food, and even in detecting landmines.

Members of non-rodent orders such as Chiroptera (bats), Scandentia (treeshrews), Insectivora (moles, shrews and hedgehogs), Lagomorpha (hares, rabbits and pikas) and mustelid carnivores such as weasels and mink are sometimes confused for rodents. Rodents have a carrier-immunity to rabies virus, making them immune to the potentially infectious and lethal disease. They are carriers for most other animal-to-human illnesses, however, and still should not be agitated.

Wood Mouse

Classification

The rodents are part of the clades: Glires (along with lagomorphs), Euarchontoglires (along with lagomorphs, primates, treeshrews, and colugos), and Boreoeutheria (along with most other placental mammals). The order Rodentia may be divided into suborders, infraorders, superfamilies and families.

Classification scheme:

ORDER RODENTIA (from Latin, rodere, to gnaw)

• Suborder Sciuromorpha
  • Family Aplodontiidae: mountain beaver
  • Family Sciuridae: squirrels, including chipmunks, woodchucks, and prairie dogs
  • Family Gliridae (also Myoxidae, Muscardinidae): dormice
• Suborder Castorimorpha
  • Superfamily Castoroidea
    • Family Castoridae: beavers
  • Superfamily Geomyoidea
    • Family Heteromyidae: kangaroo rats and kangaroo mice
    • Family Geomyidae: pocket gophers
• Suborder Myomorpha
  • Superfamily Dipodoidea
    • Family Dipodidae: jerboas and jumping mice
  • Superfamily Muroidea
    • Family Platacanthomyidae: spiny dormice
    • Family Spalacidae: mole rats, bamboo rats, and zokors
    • Family Calomyscidae: mouse-like hamsters
    • Family Nesomyidae: climbing mice, rock mice, white-tailed rat, Malagasy rats and mice
    • Family Cricetidae: hamsters, New World rats and mice, voles
    • Family Muridae: true mice and rats, gerbils, spiny mice, crested rat
• Suborder Anomaluromorpha
  • Family Anomaluridae: scaly-tailed squirrels
  • Family Pedetidae: springhares
• Suborder Hystricomorpha
  • Family incertae sedis Diatomyidae: Laotian rock rat
  • Infraorder Ctenodactylomorphi
    • Family Ctenodactylidae: gundis
  • Infraorder Hystricognathi
    • Family Hystricidae: Old World porcupines
    • Family Erethizontidae: New World porcupines
    • Family Thryonomyidae: cane rats
    • Family Petromuridae: dassie rat
    • Family Bathyergidae: African mole rats
    • Parvorder Caviomorpha
      • Family Octodontidae: octodonts
      • Family Echimyidae: spiny rats
      • Family Capromyidae: hutias
      • Family †Heptaxodontidae: giant hutias
      • Family Myocastoridae: nutria
      • Family Dasyproctidae: agoutis
      • Family Dinomyidae: pacaranas
      • Family Caviidae: cavies, including guinea pigs
      • Family Hydrochoeridae: Capybara
      • Family Chinchillidae: chinchillas and viscachas
      • Family Abrocomidae: chinchilla rats
      • Family Ctenomyidae: tuco-tucos

Alternate classifications

The above taxonomy uses the shape of the lower jaw (sciurognath or hystricognath) as the primary character. This is the most commonly used approach for dividing the order into suborders. Many older references emphasize the zygomasseteric system (suborders Protrogomorpha, Sciuromorpha, Hystricomorpha, and Myomorpha).

Several molecular phylogenetic studies have used gene sequences to determine the relationships among rodents, but these studies are yet to produce a single consistent and well-supported taxonomy. Some clades have been consistently produced such as:

• Ctenohystrica contains:
  • Ctenodactylidae (gundis)
  • Hystricognathi containing:
    • Hystricidae
    • An unnamed clade containing:
      • Phiomorpha
      • Caviomorpha

• An unnnamed clade contains:
  • Gliridae
  • Sciuroidea containing:
    • Aplodontiidae
    • Sciuridae

• Myodonta includes:
  • Dipodoidea
  • Muroidea

The positions of the Castoridae, Geomyoidea, Anomaluridae, and Pedetidae are still being debated.

References

ISBN links support NWE through referral fees

• MacClintock, D. 1970. Squirrels of North America. New York : Van Nostrand Reinhold Company.
• Nowak, R. M., and J. L. Paradiso. 1983. Walker's Mammals of the World. Baltimore, Maryland: The Johns Hopkins University Press. ISBN 0801825253
• University of California Museum of Paleontology (UCMP). 2007 "Rodentia". [1]
• Voelker, W. 1986. The Natural History of Living Mammals. Medford, New Jersey: Plexus Publishing, Inc. ISBN 0937548081

Rodent Families

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