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.

Rabbits, hares, and pikas are not rodents, but are members of the order Lagomorpha.

Rodent characteristics

Typical rodent tooth system

The incisor teeth of rodents are their most distinctive feature. An rodent's incisors grow continuously throughout 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. If their numbers were not kept in check by predators rodents would soon over run their environments.

Rodents and humans

File:Jan2306 122.jpg

Pet golden hamster

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. Among the 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.

The fur of some rodents is also an important product. The trapping of beavers for their fur played an important part in the history of North America. Some other rodent species are also trapped for fur in the wild, while the chinchilla (Chinchilla laniger) of South America is raised for its fur.

The greatest impact of rodents on humans began when agriculture began and people started to live in settled homes. At that time some rodent species moved in, especially to eat stored grain and food scraps and to benefit from warm living spaces and protection from predators. The house mouse (Mus musculus), which seems to be native from the Mediterranean area to China, and several species of rats, native to Southeast Asia, were the most successful and now live in human habitations all over the world.

Although the great majority of rodent species do no harm to humans, these commensal (which means "sharing the same table") species, especially the rats, do a tremendous amount of damage to crops and stored food. They also spread diseases, including the bubonic plague which has killed tens of millions of people through history and is still a danger today.

Rats do a lot a damage to the natural environments where they have been introduced by humans. The black rat (Rattus rattus) has contributed to the extinction of many species of birds and other animals, especially on islands (ISSG 2007). Many wild rodent species now endangered because of habitat loss and introduction of invasive species, including rats. The IUCN lists 2041 rodent species on their "Red List of Threatened Species" (IUCN 2007).

Capybara, the largest living rodent

Some species of rodents are kept as pets. One of the most popular rodent pets is the golden hamster (Mesocricetus auratus). All of the world's pet golden hamsters are descendants of one family captured in Syria in 1930 (Voelker 1986). Other rodent pets include mice, rats, and guinea pigs.

Rodents also play an important role as subjects of scientific research. One reason for this is that with their short lives many generations can be studied in a few years. Research on mice, rats, and guinea pigs has contributed greatly to our understanding of biological processes and has helped to save millions of human lives.

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.

Wood Mouse

North American porcupine

Groundhog (Marmota monax), on watch for predators

Siberian Chipmunk (Tamias sibiricus)

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, and the 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

References

ISBN links support NWE through referral fees

• IUCN Species Survival Commission (IUCN). 2007. .2006 ICUN Red List of Threatened Species. International Union for Conservation of Nature and Natural Resources. Retrieved March 3, 2007.
• Invasive Species Specialist Group (ISSG). 2007. Global invasive species database: Rattus rattus. Invasive Species Specialist Group Website. Retrieved March 3, 2007.
• 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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