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marsupial

marsupial (märsōō´pēəl), member of the order Marsupialia, or pouched mammals. With the exception of the New World opossums and an obscure S American family (Caenolestidae), marsupials are now found only in Australia, Tasmania, New Guinea, and a few adjacent islands. They are generally distinguished from placental mammals by the absence of a placenta connecting the embryo with its mother, although in a few forms the female has a rudimentary placenta that functions for a short time.

The embryo is nourished during its brief gestation by a fluid secreted by the mother's uterus. The young are born in a very undeveloped state; at birth the great gray kangaroo is about 1 in. (2.5 cm) long and the opossum about 11/2 in. (3.8 cm) long. Immediately after birth the young crawl to the mother's nipples and remain attached to them while continuing their development. As they are still too helpless to suckle, milk is squirted into them by the periodic contraction of muscles over the mother's mammary glands.

In nearly all marsupials the female's nipples are covered by a pouch, or marsupium, formed by a fold of abdominal skin. Even after the suckling stage the young return at times to the pouch for shelter and transportation. In many species the young are carried on the mother's back after the suckling stage. In addition to having a less efficient reproductive system than the placental mammals, marsupials are of generally lower intelligence.

Marsupials were once widespread over the earth, but were displaced in most regions as the more successful placental mammals evolved. The Australian region, which has been isolated from contact with other regions since the Cretaceous period, had almost no native placental mammals, and the marsupials were able to continue their evolution there without competition. They underwent an adaptive radiation in Australia comparable to that of placental mammals in the rest of the world, evolving many forms that superficially resemble various placental mammals and fill the same ecological niches. Thus, there are animals known as Tasmanian wolves (see thylacine), marsupial moles, marsupial mice, and native cats (see dasyure), which live very much like the correspondingly named placental mammals and, in many cases, are strikingly similar in appearance. See also bandicoot, numbat, phalanger, Tasmanian devil, wombat.

See H. Tyndale-Biscoe, Life of Marsupials (1973); A. K. Lee and A. Cockburn, Evolutionary Ecology of Marsupials (1985).

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Marsupialia

Marsupialia (subclass Theria, infraclass Metatheria) An order that comprises some 250 species of living marsupials and many extinct forms. In the 1960s it was divided into three suborders (Polyprotodonta, which includes the opossum-like insectivorous, carnivorous, and omnivorous forms; Diprotodontia, containing the phalangers, kangaroos, and other forms evolved from an opossum-like stock, but differing structurally from the polyprotodonts; and Caenolestoidea (classed by others as a superfamily), containing a small group of ‘opossum rats’), but nowadays it is usual to divide the marsupials into several orders: Dasyuromorphia; Didelphimorphia (see DIDELPHOIDEA); Dromiciopsia; Notoryctemorphia (see SYNDACTYLIFORMES); Paucituberculata; and Peramelemorpha; as well as the extinct Sparassodontia. These are often allocated to two cohorts: Ameridelphia and Australidelphia. In this scheme, the name Marsupialia would cease to be used formally. Marsupials are characterized principally by their method of reproduction. The egg is yolky and has a thin shell protecting it from maternal antigens. Placental development is usually very limited and except in the Peramelemorpha the allantois serves no nutritional function, but uterine milk may be taken up by the yolk sac. Within 10–12 days of the breaking of the shell, the embryo (whose fore limbs and associated neural development, mouth, and olfactory system have developed precociously) is born. It crawls into the pouch (marsupium) and attaches itself to a teat, its lips growing around the teat, which injects milk without choking the embryo. In the later stages of its development an offspring may receive high-fat, low-protein milk from one teat while a newer embryo receives high-protein, low-fat milk from another. Marsupials also differ from placentals in their dentition, in the possession of an inflected angular process to the jaw, and in the presence of two marsupial bones which articulate with the pubes. Marsupials and placental mammals apparently diverged from a common ancestor in the Cretaceous. The first marsupials were similar in general form to the opossums of America. In Australia the marsupials radiated to produce a wide array of adaptive types, while in S. America they filled the insectivorous and carnivorous niches for much of the Cenozoic, while placentals occupied the herbivorous niches.

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Marsupialia

Marsupialia (subclass Theria, infraclass Metatheria) An order that comprises some 250 species of living marsupials and many extinct forms. It is sometimes divided into three suborders (Polyprotodonta, which includes the opossum-like insectivorous, carnivorous, and omnivorous forms; Diprotodontia, containing the phalangers, kangaroos, and other forms evolved from an opossum-like stock, but differing structurally from the polyprotodonts; and Caenolestoidea (classed by others as a super-family), containing a small group of ‘opossum rats’), but nowadays it is usual to divide the marsupials into several orders, often allocated to two cohorts: Ameridelphia and Australidelphia. In this scheme, the name Marsupialia would cease to be used formally. Marsupials are characterized principally by their method of reproduction. The egg is yolky and has a thin shell protecting it from maternal antigens. Placental development is usually very limited and except in the Peramelemorpha the allantois serves no nutritional function, but uterine milk may be taken up by the yolk sac. Within 10–12 days of the breaking of the shell, the embryo (whose fore limbs and associated neural development, mouth, and olfactory system have developed precociously) is born. It crawls into the pouch (marsupium) and attaches itself to a teat, its lips growing around the teat, which injects milk without choking the embryo. In the later stages of its development an offspring may receive high-fat, low-protein milk from one teat while a newer embryo receives high-protein, low-fat milk from another. Marsupials also differ from placentals in their dentition, in the possession of an inflected angular process to the jaw, and in the presence of two marsupial bones which articulate with the pubes. Marsupials and placental mammals apparently diverged from a common ancestor in the Cretaceous. The first marsupials were similar in general form to the opossums of America. In Australia the marsupials radiated to produce a wide array of adaptive types, while in S. America they filled the insectivorous and carnivorous niches for much of the Cenozoic, while placentals occupied the herbivorous niches.

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Marsupial

Marsupial

Marsupials, also known as metatherian mammals, are an ancient and diverse mammal group. They are distinguished from other mammals by a number of cranial and skeletal characteristics, including larger numbers of teeth. Marsupials also share a unique pattern of reproduction and development of the young. Marsupial young are born at an early stage of development after a gestation period that can be as short as twelve days. After birth, they crawl over the mother's fur and skin and attach themselves to a nipple. Many, but not all, marsupials develop a pouch that protects the nursing young, and most development occurs within the pouch.

The marsupial lineage is thought to be the sister group to the lineage of placental mammals. The two groups are believed to have diverged 140 million years ago by the mid-Cretaceous, but are first known from the late Cretaceous fossil record. Marsupials have never evolved flying or marine forms, but they are morphologically diverse and occupy every other ecological niche .

Most marsupial diversity occurs in the Australasian region (about two hundred species) and in the tropical regions of Central and South America (about seventy species). Examples of marsupials are the red kangaroo (Macropus rufus ), the koala (Phascolarctos cinereus ), and the Virginia opossum (Didelphis virginiana ), the only native marsupial found in the United States and Canada.

see also Mammal

Tanya Dewey

Bibliography

Nowak, Ronald M., ed. Walker's Mammals of the World. Baltimore, MD: Johns Hopkins University Press, 1991.

Vaughan, Terry A. Mammalogy. Philadelphia, PA: Saunders College Publishing, 1986.

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marsupial

mar·su·pi·al / märˈsoōpēəl/ Zool. • n. a mammal of an order (Marsupialia) whose members are born incompletely developed and are typically carried and suckled in a pouch on the mother's belly. Marsupials are found mainly in Australia and New Guinea, although three families, including the opossums, live in America. • adj. of or relating to this order.

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marsupial

marsupial Mammal of which the female usually has a pouch (marsupium), within which the young are suckled and protected. At birth, the young are not fully formed. Most marsupials are Australasian, and include such varied types as the kangaroo, koala, wombat, Tasmanian devil, bandicoot, and marsupial mole. The only marsupials to live outside Australasia are the opossums and similar species found in the Americas. See also monotreme

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marsupial

marsupial of or resembling a pouch XVII; epithet of mammals having a pouch for their young XIX. — modL. marsüpiālis, f. L. marsūpium pouch — Gr. marsúpion, marsípion, dim. of mársipos purse, bag; see -AL1.

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marsupials

marsupials See Marsupialia.

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marsupials

marsupials See Metatheria.

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marsupial

marsupial •beau idéal, ideal, real, surreal •labial • microbial • connubial •adverbial, proverbial •prandial • radial • medial • mondial •cordial, exordial, primordial •custodial, plasmodial •preludial • collegial • vestigial •monarchial • Ezekiel • bronchial •parochial • pallial • Belial •familial, filial •proemial • binomial • Nathaniel •bicentennial, biennial, centennial, decennial, millennial, perennial, Tenniel, triennial •cranial •congenial, genial, menial, venial •finial, lineal, matrilineal, patrilineal •corneal •baronial, ceremonial, colonial, matrimonial, monial, neocolonial, patrimonial, testimonial •participial • marsupial •burial, Meriel •terrestrial •actuarial, adversarial, aerial, areal, bursarial, commissarial, filarial, malarial, notarial, secretarial, vicarial •Gabriel •atrial, patrial •vitriol •accessorial, accusatorial, advertorial, ambassadorial, arboreal, armorial, auditorial, authorial, boreal, censorial, combinatorial, consistorial, conspiratorial, corporeal, curatorial, dictatorial, directorial, editorial, equatorial, executorial, gladiatorial, gubernatorial, immemorial, imperatorial, janitorial, lavatorial, manorial, marmoreal, memorial, monitorial, natatorial, oratorial, oriel, pictorial, piscatorial, prefectorial, professorial, proprietorial, rectorial, reportorial, sartorial, scriptorial, sectorial, senatorial, territorial, tonsorial, tutorial, uxorial, vectorial, visitorial •Umbriel • industrial •arterial, bacterial, cereal, criterial, ethereal, ferial, funereal, immaterial, imperial, magisterial, managerial, material, ministerial, presbyterial, serial, sidereal, venereal •mercurial, Muriel, seigneurial, tenurial, Uriel •entrepreneurial •axial, biaxial, coaxial, triaxial •uncial • lacteal •bestial, celestial •gluteal •convivial, trivial •jovial, synovial •alluvial, diluvial, fluvial, pluvial •colloquial, ventriloquial •gymnasial • ecclesial • ambrosial

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