Rodent

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See Classification Section

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The order Rodentia is the most numerous 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 except Antarctica (they are the only placental order other than bats (Chiroptera) to reach Australia without human introduction), most islands, and in all habitats bar the oceans.

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Groups commonly confused with rodents, or erroneously thought to be rodents, include the aforementioned Chiroptera (bats), Scandentia (tree shrews), Insectivora (moles, shrews and hedgehogs), and Lagomorpha (hares, rabbits and pikas).

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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.

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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. These teeth have enamel on the outside and exposed dentine on the inside, so they self-sharpen during gnawing. Rodents lack canines, and have a space between their incisors and premolars. Nearly all rodents feed on plants, seeds in particular, but there are a few exceptions which eat insects or even fish.

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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 a model organism in animal testing, and even in detecting landmineshttp://www.theage.com.au/articles/2004/05/18/1084783512636.html?oneclick=true.

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Order: Order (from Latin ordo "row, rank, series, arrangement", Old French ordre from the Latin accusative, ordinem, attested in English from the 1220s). The word conveys a notion of "a system of parts subject to certain uniform, established ranks or proportions", an idea very central to scholastic thoug...

Species: In biology, the most commonly used definition of species was first coined by Ernst Mayr. Species are "groups of actually or potentially interbreeding natural populations which are reproductively isolated from other such groups" (however, see other definitions of species below)....

Antarctica: :For the Kim Stanley Robinson novel see Antarctica (novel)...