Rodents are the largest group of mammals. The word rodent comes from the Latin verb 'to gnaw.' Rodents have upper and lower pairs of incisor teeth which keep on growing. They live in every area of the world except Antarctica, New Zealand, and a few Arctic islands. Besides rats and mice, rodents include beavers, porcupines, squirrels, and marmots. There is a gap between the pairs of incisors and the teeth farther back in their mouths, called the cheek teeth. While the animal chews, the incisors from the top do not meet the bottom ones, and the cheek teeth top and bottom do not meet.
The smallest rodent is Delany's swamp mouse which weighs from five to seven grams and has a body that is five to six centimeters long. It lives in marshes and mountain forests in Africa. A capybara of Central and South America is the largest rodent. It weighs from 77-146 pounds.
Rodents can be deadly for humans and at the least pests. Certain species carry diseases like Rocky Mountain spotted fever, plague or typhus. Some rodents can be a source of food or fur. They are used for genetic research. Some are household pets, like gerbils and hamsters.
Diets of most rodents include both vegetable and animal matter. Some sleep all day and are active at night. Some are active all day and sleep at night. Some are active some of the day and some of the night. Rodents either eat their food where they find it or carry it where they can store it. Rodents who live in dry areas can get their water from their food.
Types of homes for rodents are varied. Some live in holes in trees or cracks in rocks. Some live in burrows or hidden nests on the floor of the forest. Some build structures of leaves and twigs in the tops of trees or homes from piled up plant matter in ponds. Some have intricate mazes of tunnels. Rodents may be active all year or go through periods of hibernation.
The body form of a squirrel is good for clinging to the bark of a tree with its claws and running up and down tree trunks or leaping from one tree to the other. They also can scamper quickly across the ground. Some squirrels are burrowers.
Other types of rodents have body forms which suit their specific needs. Those which live in trees have a prehensile tail, long and able to curl around branches. Others need to glide between trees so have fur-covered membranes between fingers. Beavers, muskrats and water rats live in semiaquatic environments. They can dig in the water but live in a den in the ground. Jumping mice and kangaroo rats have short forelimbs and long hind legs for pushing off and jumping. All rodents have the same types of tools used to cut, slice, dig, kill, chew, gouge or bring down tall trees.
A rodent's forelimb usually has five digits (fingers or toes) and includes an opposable thumb, like a human. The back limb has three to five digits. The nails of rodents which burrow are long and strong. Those which live in the trees (arboreal) have short and sharp nails.
Rodent species have various forms of moving along (locomotion). Some hop, like kangaroo mice and hopping mice. Some glide (flying squirrels). The agouti has nails like hooves and runs like an antelope. Most have tails. Some use them for communication. A beaver slaps his tail on the water. House mice rattle their tails to give warning of danger. Most rodents have excellent senses of hearing, sight, and smell. Many have sensitive whiskers for touching. Some have cheek pouches lined with fur. Beavers can alter the course of rivers and provide bigger wetland habitats. Prairie dogs play a role in soil aeration. They also increase the organic composition of the soil.
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