The Order Rodentia
Rodents are the most successful of modern mammals, apart from man, and are found in all parts of the world. They are easily identified by the long pair of chisel-like incisor teeth (with enamel on the front surface only) projecting from each jaw at the front of the mouth; these teeth grow continuously and if for any reason they are not worn down by gnawing, the tips may grow past each other and perforate the palate. In some rodents the lips can be closed behind the incisors so that athe animals can gnaw without dirt entering their mouths. The scrotum, unlike that of the lagomorphs, is behind the penis, which has a bone. Three sub-orders are recognised on the basis of the position and structure of the jaw muscles.
Sub-Order Sciuromorpha
Squirrel-like rodents
This sub-order includes squirrels, marmots, gophers and beavers.
Family Aplodontidae
There is one species: Sewellel Aplodontia rufa, a thick-set, heavy, burrowing animal, often called the mountain beaver. It lives in forests, near streams, in western North America.
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Family Sciuridae
Squirrels: 250 species
Found all over the world except Australia, squirrels are active during the day and generally live in trees, although some species are ground-dwelling and dig burrows. They have large eyes, and many are brightly coloured.
Family Geomyidae
Pocket gophers: 30 species
These North American burrowing rodents have strong digging claws and two long fur-lined external cheek pouches, used for carrying food, which the animal can turn inside-out for cleaning. They spend most of their lives underground.
Family Heteromyidae
Kangaroo rats and pocket mice: 70 species
Occurring from western North America to Venezuela, these animals have long hind limbs for jumping and cheek pouches like those of pocket gophers. They make burrows under bushes, and become torpid in cold weather.
Family Castoridae
There is one species - the beaver Castor fiber found in rivers and lakes in Europe, Asia and North America, the beaver is a water-dwelling rodent, with dense underfur overlaid with coarse guard hairs, ears and eyes which can be closed under water, webbed feet and a broad, paddle-shaped scaly tail. The dam-building activities of beavers can create large ponds and greatly change whole environments.
Family Anomaluridae
Scaly-tailed squirrels: 9 species
Except for members of the genus Zenkerella, all scaly-tailed squirrels have a gliding skin or membrane between the limbs, extending to the tail. All scaly-tailed squiarrels have two overlapping rows of scales on the underside of the tail which act as an 'anti-skid' device when they land on a tree-trunk.
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Family Pedetidae
There is one species - Springhaas, or Cape jumping hare, Pedetes capensis which lives in grasslands and open bush in eastern and southern Africa. Except for the bushy tail, the springhaas has a kangaroo-like appearance with long hind legs and ears and a soft coat.

Sub-Order Myomorpha
Mouse-like rodents
This large group contains more than 1000 species of rodents.
Family Cricetidae
Hamsters and allies: 570 species
Most members of this family burrow. Many have thick-set bodies and short tails and legs. Included in this family aare the musk rat Ondatra zibethicus; the brown lemming Lemmus lemmus; the short-tailed vole Microtus agrestris.
Family Spalacidae
Mediterranean mole-rats: 3 species
These rodents have long bodies; short legs; soft, dense, reversible fur, tactile bristles on the snout; no external eye openings and no external ears. They are found in eastern Europe and south-western Asia.
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Family Rhizomyidae
Bamboo rats and African mole-rats: 18 species
With their compact bodies adapted for burrowing and their long incisor teeth uncovered by the lips, these rats resemble the American pocket gophers, except that they have no cheek pouches.
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Family Muridae
Old World rats and mice: 500 species
Most of the rats and mice in this family are small animals with naked, scaly tails and long snouts. The structure of their teeth distinguishes them from the Cricetidae.

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Family Gliridae
Dormice: 10 species
Dormice, found in Europe, Asia and Africa, have rather bushy tails, soft coats, short bodies, short legs and toes, and curved claws for climbing. In the northern part of their range they become fat in autumn and are dormant from October to April.
Family Platacanthomyidae
Spiny dormouse and Chinese pygmy dormouse: 2 species
These Asian rodents look like dormice except that the tail is scaly at the base and ends in a brush. They have large ears and long hind feet.
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Family Seleviniidae
There is one species: Desert dormouse Selevinia betpakdalaensis a rare animal discovered in 1938 in the clay and sandy deserts of Kazakhstan. It has a round body and long, non-bushy tail. It moults in an unusual way - the hair comes off in patches, along with the skin.
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Family Zapodidae
Birch mice and jumping mice: 11 species
These small mouse-like animals are found in forests, meadows and swamps in northern Europe, Asia and North America. They have internal cheek pouches, long hind legs used for jumping and a long tail for balancing.
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Family Dipodidae
Jerboas: 25 species
These animals, found in Asia and northern Africa, are remarkably well adapted for jumping, with hind legs at least four times as long as the front legs, elongated feet with three central bones fused to form a single bone for strength and support, and long tails.

Sub-Order Hystricomorpha
Porcupine-like rodents
VALIGN="TOP"> Family Hystricidae
Old World porcupines: 20 species
These large, thick-set short-legged rodents from Africa, Italy and southern Asia have long, sharp quills for defence in addition to hair on their bodies and tails.
Family Erethizontidae
New World porcupines: 23 species
These porcupines have shorter spines than their Old World counterparts; some of the spines are barbed. Their feet are modified for life in the trees - the sole is widened and the first toe on the hind foot is replaced by a broad, movable pad.
Family Caviidae
Cavies or guinea-pigs: 23 species
Members of this South American family are found in rocky areas, savannas, forest edges and swamps. They have fairly coarse coats, large head, long thin limbs and rudimentary tails.
Family Hydrochoeridae
There is one species: the Capybara Hydrochoerus hydrochaeris - the largest living rodent. The capybara is semi-aquatic, living in groups by rivers and lakes in Central and South America. It has a broad head, short rounded ears and webbed feet. There is a bare raised gland on the top of the snout in the adult male.
Family Dinomyidae
There is one species: the Pacarana Dinomys branickii - found in forests on the lower slopes of the Andes. It is thick-set with a short stout furry tail, short ears and limbs and long claws and whiskers.
Family Dasyproctidae
Agoutis, acuchis and pacas: 30 species
Members of this family have long legs, small thick hoof-like claws and a coarse thick coat.
Family Chinchillidae
Chinchillas and viscachas: 6 species
Most chinchillas are found in the foothills of the southern Andes. They have a large head, broad snout, large eyes and ears, and a long fine coat. Their hind limbs are adapted for jumping, but they run, leap or creep on all fours.
Family Capromyidae
Coypus and hutias: 10 species
A family of robust, often aquatic rodents; its members have small ears and eyes, short limbs, prominent claws, and a sparsely haired tail.
Family Octodontidae
Octodonts: 8 species
These rat-like animals have long, silky body fur and coarsely haired tails which some species carry erect when running. They are found in South America from coastal regions up to 10,000 ft and live in burrows.
Family Ctenomyidae
Tuco-tucos: 26 species
Tuco-tucos resemble pocket gophers but have no cheek pouches. They make their burrows in dry sandy soil.
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Family Abrocomidae
Chinchilla rats: 2 species
These rodents, which have long dense underfur with fine guard hairs, are rat-like in appearance, with large eyes and ears, finely haired tails, short limbs and weak claws which are hollow underneath.
Family Echimyidae
Spiny rats: 75 species
Rat-like in general appearance, these rodents of Central and South America generally have bristly fur.
Family Thryonomyidae
Cane rats: 6 species
These rodents, widespread in Africa, have bristly hairs, flattened and grooved along their upper surfaces, growing in groups of five or six.
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Family Petromyidae
There is one species: Rock rat Petromus typicus - a squirrel-like rodent from south-western Africa. It has flexible ribs which enable it to squeeze through narrow crevices.
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Family Bathyergidae
African mole-rats: 50 species
Like other burrowing mammals, mole-rats have stocky bodies, strong feet, short tails and limbs, and small eyes and ears.
Family Ctenodactylidae
Gundis and Speke's pectinator: 8 species
The gundis of northern Africa look like guinea-pigs. They have soft fur and comb-like brushes of bristles on two digits of the hind feet for cleaning fur.
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