jumping mouse, (subfamily Zapodinae), any of five species of small leaping rodents found in North America and China. Jumping mice weigh from 13 to 26 grams (0.5 to 0.9 ounce) and are 8 to 11 cm (3.1 to 4.3 inches) long, not including the scantily haired tail, which is longer than the body. Their glossy fur is soft or slightly coarse; coloration is tripartite: brown on top from nose to rump, grayish to rust-coloured on the sides, and white on the underparts. The tail is brown above and white below.
Jumping mice normally run on all four legs or bounce along in a series of short hops, but when alarmed they leap powerfully yet erratically up to 4 metres (13 feet), using their disproportionately long hind legs. They are balanced by the slender tail.
Generally terrestrial, these rodents are also agile shrub climbers and excellent swimmers. Their spherical nests are constructed of vegetation and are found in abandoned burrows of other animals, on the ground beneath logs or heavy brush, and sometimes in low shrubs and trees. Jumping mice eat a varied diet of fungi, fruit, seeds, invertebrates, and occasionally mollusks and small fish. During the winter they retreat underground to hibernate.
North American jumping mice, though common in some areas, are rarely seen because they are completely nocturnal. The woodland jumping mouse (Napaeozapus insignis) lives in moist forests of eastern North America. The meadow, Pacific, and western jumping mice (Zapus hudsonius, Z. trinotatus, and Z. princeps, respectively) range over much of North America, in grasslands as well as riverine and wet meadow habitats of cool and moist forests. The only species found outside North America is the Sichuan jumping mouse (Eozapus setchuanus), which inhabits cool and wet mountain forests of southern China. It is sometimes incorrectly included in the genusZapus. Very little is known about its natural history.
Jumping mice constitute the subfamily Zapodinae. Along with birch mice and the more distantly related jerboas, jumping mice are classified in the family Dipodidae rather than with the “true” mice (family Muridae). Fossils of four extinct genera provide evolutionary history of jumping mice from the Middle Miocene Epoch (16.4 million to 11.2 million years ago) in North America and the Late Miocene Epoch (11.2 million to 5.3 million years ago) in Eurasia.
rodent, (order Rodentia), any of more than 2,050 living species of mammals characterized by upper and lower pairs of ever-growing rootless incisor teeth. Rodents are the largest group of mammals, constituting almost half the class Mammalia’s approximately 4,660 species. They are indigenous to every land area except Antarctica, New Zealand, and a few Arctic and other oceanic islands, although some species have been introduced even to those places through their association with humans. This huge order of animals encompasses 27 separate families, including not only the “true” rats and mice (family Muridae) but also such diverse groups as porcupines, beavers, squirrels, marmots, pocket gophers, and chinchillas.
All rodents possess constantly growing rootless incisors that have a hard enamel layer on the front of each tooth and softer dentine behind. The differential wear from gnawing creates perpetually sharp chisel edges. Rodents’ absence of other incisors and canine teeth results in a gap, or diastema, between incisors and cheek teeth, which number from 22 (5 on each side of the upper and lower jaws) to 4, may be rooted or rootless and ever-growing, and may be low- or high-crowned. The nature of the jawarticulation ensures that incisors do not meet when food is chewed and that upper and lower cheek teeth (premolars and molars) do not make contact while the animal gnaws. Powerful and intricately divided masseter muscles, attached to jaw and skull in different arrangements, provide most of the power for chewing and gnawing.
The range in body size between the mouse (18 grams [0.64 ounce], body 12 cm [4.7 inches] long) and the marmot (3,000 grams, body 50 cm long) spans the majority of living rodents, but the extremes are remarkable. One of the smallest is Delany’s swamp mouse (Delanymys brooksi), associated with bamboo in the marshes and mountain forests in Africa. It weighs 5 to 7 grams, and the body is 5 to 6 cm long. The largest is the capybara (Hydrochoerus hydrochaeris) of Central and South America, which weighs 35 to 66 kg (77 to 146 pounds) and stands 50 to 60 cm at the shoulder, with a body 100 to 135 cm long. Some extinct species were even larger, attaining the size of a black bear or small rhinoceros. The largest rodent ever recorded, Josephoartigasia monesi, lived some two to four million years ago, during the Pleistocene and Pliocene epochs; by some estimates it grew to a length of about 3 metres (10 feet) and weighed nearly 1,000 kg.
Importance to humans
Rodents have lived on the planet for at least 56 million years and modern humans for less than one million, but the consequences of their interactions during that short overlap of evolutionary time have been profound. For rodents, early humans were just another predator to avoid, but with Homo sapiens’ transition from nomadic hunting and gathering to sedentary agricultural practices, humans became a reliable source of shelter and food for those species having the innate genetic and behavioral abilities to adapt to man-made habitats. The impact of these species upon human populations ranges from inconvenient to deadly. Crops are damaged before harvest; stored food is contaminated by rodent waste; water-impounding structures leak from burrowing; and objects are damaged by gnawing. Certain species are reservoirs for diseases such as plague, murinetyphus, scrub typhus, tularemia, rat-bite fever, Rocky Mountain spotted fever, and Lassa fever, among others. Only a few species are serious pests or vectors of disease (see house mouse and rat), but it is these rodents that are most closely associated with people.
Rodents may be diurnal, nocturnal, or sometimes active part of the day and night. Although some species are herbivorous, diets of most include vegetable and animal matter. Others are opportunistic generalists, and some are specialized predators, not only of arthropods (see grasshopper mouse) but sometimes of vertebrates. Food is either eaten where gathered or carried to burrows and stored (see pocket gopher, pocket mouse, African pouched rat, and hamster). Species living in arid habitats and on oceanic islands are able to obtain their water requirements from their food. A wide variety of shelters are used or constructed; these range from tree holes, rock crevices, or simple burrows to hidden nests on the forest floor, leaf and stick structures in tree crowns, mounds of cut vegetation built in aquatic environments, or complex networks of tunnels and galleries. Rodents may be active all year or enter periods of dormancy or deep hibernation. Breeding time and frequency, length of gestation, and litter size vary widely, but two of the most prolific are both associated with humans. The brown rat (Rattus norvegicus) can give birth to litters of up to 22 offspring, and the house mouse (Mus musculus) can produce up to 14 litters annually. Population size may remain stable or fluctuate, and some species, most notably lemmings, migrate when populations become excessively large.
The body form of treesquirrels may be the model for the earliest, and presumably generalized, rodents (genus Paramys). With their ability to adhere to bark with their claws, squirrels adeptly scamper up tree trunks, run along branches, and leap to adjacent trees; but they are equally agile on the ground, and some are capable swimmers. Burrowers are also represented in the form of long-tailed ground squirrels.
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The specialized body forms of other kinds of rodents tie them closer to particular locomotor patterns and ecologies. Some strictly arboreal species have a prehensile tail; others glide from tree to tree supported by fur-covered membranes between appendages (see flying squirrel and anomalure). Highly specialized fossorial (burrowing) rodents, including blind mole rats, blesmols, and ground squirrels, are cylindrical and furry with protruding, strong incisors, small eyes and ears, and large forefeet bearing powerful digging claws. Semiaquatic rodents such as beavers, muskrats, nutrias, and water rats possess specialized traits allowing them to forage in aquatic habitats yet den in ground burrows. Terrestrial leaping species, such as kangaroo rats, jumping mice, gerbils, and jerboas, have short forelimbs, long and powerful hind limbs and feet, and a long tail used for balance. Body forms of some rodents converge on those in nonrodent orders, resembling shrews, moles, hares, pikas, pigs, or small forest deer. There is also convergence between distantly related groups of rodents in particular body forms and associated natural histories.
Regardless of body form, all rodents share the same basic tools that, as mammologists Emmons and Feer noted, “can be used to cut, pry, slice, gouge, dig, stab, or delicately hold like a pair of tweezers; they can cut grass, open nuts, kill animal prey, dig tunnels and fell large trees.”
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