Marsupials

Resources

Marsupials belong to the order Marsupalia, one of three subclasses of mammals (Metatheria). Marsupials are named for the marsupium, which means “pouch” in Latin; most female marsupials carry their young in pouches.

The order Marsupalia includes eight families, 75 genera, and 250 species. Marsupials are divided into two groups based on the number and shape of the incisor teeth. One group has numerous small incisors (the Polyprotodontia) and includes the carnivorous and insectivorous marsupial mice and American opossum. The second group has a few large incisors (Diprotodontia) and includes the herbivorous marsupials such as kangaroos and wallabies.

The majority of marsupial species, such as kangaroos, wallabies, koalas, bandicoots, wombats, and Tasmanian devils inhabit the Australasian region (Australia, New Guinea, and the surrounding islands) to the east of Lombok in Indonesia, which marks the boundary between the Australian and Asian fauna. Approximately one-third of the species, most of which are opossums, are native to the Americas.

Marsupials live underground (i.e. marsupial moles), on land (kangaroos), in trees (tree kangaroos and koalas), and in water (yapok), and inhabit rain-forests, deserts, and temperate regions. Many species are nocturnal, while others are active by day. Marsupials may be herbivorous, carnivorous, insectivorous, or a combination of the three. Marsupials range in size from mouse-sized to as large as adult humans.

All marsupials are born partially developed, small, blind, hairless; they have well-developed front legs with sharp claws and poorly developed hind legs. Immediately after birth, marsupial embryos crawl out of the birth canal using their front claws into the marsupium (pouch) where they attach themselves to a milk-secreting teat (nipple) for nourishment. The young marsupials are so helpless that they cannot suck milk right away. Contractions of muscles around the teat periodically squirt milk into the mouths of the attached embryos. The marsupial pouch helps keep the young attached to a teat. Newborn marsupials born to species without pouches stay attached by holding on to their mothers with their claws, and are aided by a swollen teat, which fills the baby’s mouth and makes it difficult to detach. Female marsupials carry their young everywhere they go. When the young can no longer fit in the pouch or become too large for the mother to carry around, they detach and begin to live independently.

The oldest known fossils of marsupials date from the upper Cretaceous period (65-100 million years ago). Marsupials were once a dominant group with a wide distribution, and in the past were well represented in South America. The opossums of the Americas are extremely adaptable and some species have increased in number. The marsupial fauna of Australasia remained intact due to the isolation of this area from the rest of the world for millions of years, but many species are currently on the endangered list. Encroaching agriculture, urban sprawl, and the introduction of placental mammals have put some species of marsupial in danger of extinction. A century ago, the kangaroo skins were in great demand. Kangaroo hides have been used for leather and their meat used for both human consumption and pet foods. Some kangaroo species considered by farmers to be pests have been slaughtered in great numbers. Today, conservation groups, wild animal refuges and sanctuaries, and cooperation from ranchers and farmers are helping to keep the current populations of marsupials protected.

See also Anteaters; Marsupial cats; Marsupial rats and mice; Numbat; Phalangers; Tasmanian devil.

Resources

BOOKS

Lavine, Sigmund A. Wonders of Marsupials. New York: Dodd, Mead & Company, 1978.

Lyne, Gordon. Marsupials and Monotremes of Australia. New York: Taplinger, 1967.

Morcombe, Michael. Australian Marsupials and Other Native Animals. New York: Charles Scribner’s Sons, 1972.

OTHER

University of California Museum of Paleontology. “Marsupial Mammals” <http://www.ucmp.berkeley.edu/mammal/marsupial/marsupial.html> (accessed December 3, 2006).

University of Michigan Museum of Zoology: Animal Diversity Web. “Infraclass Metatheria (Marsupial Mammals)” <http://animaldiversity.ummz.umich.edu/site/accounts/information/Metatheria.html> (accessed December 2, 2006]

Christine Miner Minderovic

Marsupials

Marsupials belong to the order Marsupalia, one of three subclasses of mammals (Metatheria). Marsupials are named for the marsupium, which means pouch in Latin; most female marsupials carry their young in pouches. The order Marsupalia includes eight families, 75 genera, and 250 species . Marsupials are divided into two groups based on the number and shape of the incisor teeth. One group has numerous small incisors (the Polyprotodontia) and includes the carnivorous and insectivorous marsupial mice and American opossum. The second group has a few, large incisors (Diprotodontia) and includes the herbivorous marsupials such as kangaroos and wallabies . The majority of species of marsupials, such as kangaroos, wallabies, koalas , bandicoots , wombats , and Tasmanian devils inhabit the Australasian region (Australia, New Guinea, and the surrounding islands) to the east of Lombok in Indonesia, which marks the boundary between the Australian and Asian fauna . Approximately one-third of the species, most of which are opossums , are native to the Americas. Marsupials live underground (i.e. marsupial moles ), on land (kangaroos), in trees (tree kangaroos and koalas), and in water (yapok), and inhabit rainforests, deserts, and temperate regions. Many species are nocturnal, while others are active by day. Marsupials may be herbivorous, carnivorous, insectivorous, or a combination of the three. Marsupials range in size from mouse-size to as large as adult humans.

All marsupials are born partially developed, and are small, blind, hairless; they have well-developed front legs with sharp claws and poorly developed hind legs. Immediately after birth , marsupial embryos crawl out of the birth canal using their front claws into the marsupium (pouch) where they attach themselves to a milk-secreting teat (nipple) for nourishment. The young marsupials are so helpless that they cannot suck milk right away. Contractions of muscles around the teat periodically squirt milk into the mouths of the attached embryos. The marsupial pouch helps keep the young attached to a teat. Newborn marsupials, born to species without pouches, stay attached by holding on to their mothers with their claws, and are aided by a swollen teat, which fills the baby's mouth, and makes it difficult for the young to detach. Female marsupials carry their young everywhere they go. When the young can no longer fit in the pouch or become too large for the mother to carry around, they detach and begin to live independently.

The oldest known fossils of marsupials date from the upper Cretaceous period (65–100 million years ago). Marsupials were once a dominant group with a wide distribution, and in the past were well represented in South America . The opossums of the Americas are extremely adaptable and some species have increased in number. The marsupial fauna of Australasia remained intact due to the isolation of this area from the rest of the world for millions of years, but many species are currently on the endangered list. Encroaching agriculture, urban sprawl, and the introduction of placental mammals have put some species of marsupial in danger of extinction . A century ago, the skins of large kangaroos were in great demand. Kangaroo hides have been used for leather and their meat used for human consumption, and for pet foods. Some species of kangaroo considered by farmers to be pests have been slaughtered in great numbers. Today, conservation groups, wild animal refuges and sanctuaries, and cooperation from ranchers and farmers are helping to keep the current populations of marsupials protected.

See also Anteaters; Marsupial cats; Marsupial rats and mice; Numbat; Phalangers; Tasmanian devil.

Resources

books

Lavine, Sigmund A. Wonders of Marsupials. New York: Dodd, Mead & Company, 1978.

Lyne, Gordon. Marsupials and Monotremes of Australia. New York: Taplinger, 1967.

Morcombe, Michael. Australian Marsupials and Other NativeAnimals. New York: Charles Scribner's Sons, 1972.

Christine Miner Minderovic

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.

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.

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.