Opossum
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Order: Didelphimorphia
Family: Didelphidae

[Photo] Virginia Opossum, Didelphis virginiana, shot was taken though glass door. Photo by http://en.wikipedia.org/wiki/User:Sirevil License: public domain.

Didelphimorphia is the order of common opossums of the Western Hemisphere. Opossums probably diverged from the basic South American marsupials in the late Cretaceous or early Paleocene. A sister group is Paucituberculata (shrew opossums). They are commonly also called "possums," though that term is also applied to Australian fauna of the suborder Phalangeriformes. The Virginia Opossum is the original animal named "opossum". The word comes from Algonquian wapathemwa. Colloquially, the Virginia opossum is frequently called simply possum.

Didelphimorphs are small to medium-sized marsupials, about the size of a large house cat. They tend to be semi-arboreal omnivores, although there are many exceptions. Most members of this taxon have long snouts, a narrow braincase, and a prominent sagittal crest. The dental formula (one side of one jaw) includes five incisors (four on the lower jaw), one canine, three premolars and four tricuspid molars. By mammal standards, this is a very full jaw. The incisors are very small, the canines large.

Didelphimorphs have a plantigrade stance (feet flat on the ground) and the hind feet have an opposable digit with no claw. Like some primates, opossums have prehensile tails. The stomach is simple, with a small cecum. Opossum reproductive systems are extremely basic, with a reduced marsupium. This means that the young are born at a very early stage. The species are moderately sexually dimorphic with males usually being somewhat larger than females. The largest difference between the opossum and other sexually reproductive animals is the bifurcated penis of the male and bifurcated vagina of the female (the source of the Latin "didelphis," meaning double-wombed).

Didelphimorphs are opportunistic omnivores with a very broad range of diet. Their unspecialized biology, flexible diet and reproductive strategy make them successful colonizers and survivors in unsettled times. Originally native to the eastern United States, the Virginia Opossum was intentionally introduced into the west during the Great Depression, probably as a source of food. Its range has been expanding steadily northwards, thanks in part to more plentiful, man-made sources of fresh water, increased shelter due to urban encroachment, and milder winters. Its range has extended into Ontario, Canada, and it has been found farther north than Toronto.

Opossums are usually nomadic, staying in one area as long as food and water are easily available. Though they will temporarily occupy abandoned burrows, they do not dig or put much effort into building their own. They favor dark, secure areas, below ground or above.

When threatened or harmed, they will "play possum", mimicking the appearance and smell of a sick or dead animal. The lips are drawn back, teeth are bared, saliva foams around the mouth, and a foul-smelling fluid is secreted from the anal glands. The physiological response is involuntary, rather than a conscious act. Their stiff, curled form can be prodded, turned over, and even carried away. Many injured opossums have been killed by well-meaning people who find a catatonic animal and assume the worst. The best thing to do upon finding an injured or apparently dead opossum is to leave it in a quiet place with a clear exit path. In minutes or hours, the animal will regain consciousness and escape quietly on its own.

Adult opossums do not hang from trees by their tails, though babies may dangle temporarily. Their prehensile tails are not strong enough to support a mature adult's weight. Instead, the opossum uses its tail as a brace and a fifth limb when climbing. The tail is occasionally used as a grip to carry bunches of leaves or bedding materials to the nest. A mother will sometimes carry her young upon her back, where they will cling tightly even when she is climbing or running.

Threatened opossums (especially male) will growl deeply, raising the pitch as the threat becomes more urgent. Males make a clicking "smack" noise out of the side of their mouths as they wander in search of a mate, and females will sometimes repeat the sound in return. When separated or distressed, baby opossums will make a sneezing noise to signal their mother.

Opossums have a remarkably robust immune system, and show partial or total immunity to the venom of rattlesnakes, cottonmouths, and other pit vipers. Thanks to their lower blood temperature, rabies is almost unknown in opossums.

The opossum lifespan is unusually short for a mammal of its size, usually only 2 to 4 years. Senescence is rapid.

An early description of the opossum comes from explorer John Smith, who wrote in Map of Virginia, with a Description of the Countrey, the Commodities, People, Government and Religion in 1608 that "An Opassom hath an head like a Swine, and a taile like a Rat, and is of the bignes of a Cat. Under her belly she hath a bagge, wherein she lodgeth, carrieth, and sucketh her young." The Opossum was more formally described in 1698 in a published letter entitled "Carigueya, Seu Marsupiale Americanum Masculum. Or, The Anatomy of a Male Opossum: In a Letter to Dr Edward Tyson," from Mr William Cowper, Chirurgeon, and Fellow of the Royal Society, London, by Edward Tyson, M. D. Fellow of the College of Physicians and of the Royal Society. The letter suggests even earlier descriptions.

Use as food
The opossum was a favorite game animal in the United States, and in particular the southern regions which have a large body of recipes and folklore relating to the opossum. Opossum was once widely consumed in the United States where available as evidenced by recipes in older editions of The Joy of Cooking. In Dominica and Trinidad opossum or "manicou" is popular and can only be hunted during certain times of the year due to over-hunting; the meat is traditionally prepared by smoking then stewing. The meat is light and fine grained, but the musk glands must be removed as part of preparation. The meat can be used in place of rabbit and chicken in recipes. The cousin of the opossum, the possum, found in Australia (and introduced to New Zealand) is consumed in a similar manner. (Davidson, 1999)

Historically, hunters in the Caribbean would place a barrel with fresh or rotten fruit to attract opossums who would feed on the fruit or insects. Cubans growing up in the mid-twentieth century tell of brushing the maggots out of the mouths of "manicou" caught in this manner to prepare them for consumption. It is said also that the gaminess of the meat causes gas.

In Mexico, opossums are known as "tlacuache" or "tlaquatzin". Their tails are eaten as a folk remedy to improve fertility.

Opossum oil (Possum grease) is high in essential fatty acids and has been used as a chest rub and a carrier for arthritis remedies given as topical salves.

Classification
Family Didelphidae

Subfamily Caluromyinae

Genus Caluromys
Subgenus Mallodelphys
Derby's Woolly Opossum, Caluromys derbianus
Brown-eared Woolly Opossum, Caluromys lanatus
Subgenus Caluromys
Bare-tailed Woolly Opossum, Caluromys philander

Genus Caluromysiops
Black-shouldered Opossum, Caluromysiops irrupta

Genus Glironia
Bushy-tailed Opossum, Glironia venusta

Subfamily Didelphinae

Genus Chacodelphys
Chacoan Pygmy Opossum (Chacodelphys formosa)

Genus Chironectes
Yapok or Water Opossum (Chironectes minimus)

Genus Cryptonanus
Agricola's Gracile Opossum (Cryptonanus agricolai)
Chacoan Gracile Opossum (Cryptonanus chacoensis)
Bolivian Gracile Opossum (Cryptonanus guahybae)
Red-bellied Gracile Opossum (Cryptonanus ignitus)
Rio Grande do Sul Gracile Opossum (Cryptonanus unduaviensis)

Genus Didelphis
White-eared Opossum (Didelphis albiventris)
Big-eared Opossum (Didelphis aurita)
Guianan White-eared Opossum (Didelphis imperfecta)
Common Opossum (Didelphis marsupialis)
Andean White-eared Opossum (Didelphis pernigra)
Virginia Opossum (Didelphis virginiana)

Genus Gracilinanus
Aceramarca Gracile Opossum (Gracilinanus aceramarcae)
Agile Gracile Opossum (Gracilinanus agilis)
Wood Sprite Gracile Opossum (Gracilinanus dryas)
Emilia's Gracile Opossum (Gracilinanus emilae)
Northern Gracile Opossum (Gracilinanus marica)
Brazilian Gracile Opossum (Gracilinanus microtarsus)

Genus Hyladelphys
Kalinowski's Mouse Opossum (Hyladelphys kalinowskii)

Genus Lestodelphys
Patagonian Opossum (Lestodelphys halli)

Genus Lutreolina
Lutrine or Thick-tailed Opossum (Lutreolina crassicaudata)

Genus Marmosa
Heavy-browed Mouse Opossum (Marmosa andersoni)
Rufous Mouse Opossum (Marmosa lepida)
Mexican Mouse Opossum (Marmosa mexicana)
Linnaeus's Mouse Opossum (Marmosa murina)
Quechuan Mouse Opossum (Marmosa quichua)
Robinson's Mouse Opossum (Marmosa robinsoni)
Red Mouse Opossum (Marmosa rubra)
Tyleria Mouse Opossum (Marmosa tyleriana)
Guajira Mouse Opossum (Marmosa xerophila)

Genus Marmosops
Bishop's Slender Opossum (Marmosops bishopi)
Narrow-headed Slender Opossum (Marmosops cracens)
Marmosops creightoni
Dorothys' Slender Opossum (Marmosops dorothea)
Dusky Slender Opossum (Marmosops fuscatus)
Handley's Slender Opossum (Marmosops handleyi)
Tschudi's Slender Opossum (Marmosops impavidus)
Gray Slender Opossum (Marmosops incanus)
Panama Slender Opossum (Marmosops invictus)
Junin Slender Opossum (Marmosops juninensis)
Neblina Slender Opossum (Marmosops neblina)
White-bellied Slender Opossum (Marmosops noctivagus)
Delicate Slender Opossum (Marmosops parvidens)
Brazilian Slender Opossum (Marmosops paulensis)
Pinheiro's Slender Opossum (Marmosops pinheiroi)

Genus Metachirus
Brown Four-eyed Opossum (Metachirus myosuros)

Genus Micoureus
Alston's Mouse Opossum (Micoureus alstoni)
White-bellied Woolly Mouse Opossum (Micoureus constantiae)
Woolly Mouse Opossum (Micoureus demerarae)
Tate's Woolly Mouse Opossum (Micoureus paraguayanus)
Little Woolly Mouse Opossum (Micoureus phaeus)
Bare-tailed Woolly Mouse Opossum (Micoureus regina)

Genus Monodelphis
Sepia Short-tailed Opossum (Monodelphis adusta)
Northern Three-striped Opossum (Monodelphis americana)
Northern Red-sided Opossum (Monodelphis brevicaudata)
Yellow-sided Opossum (Monodelphis dimidiata)
Gray Short-tailed Opossum (Monodelphis domestica)
Emilia's Short-tailed Opossum (Monodelphis emiliae)
Amazonian Red-sided Opossum (Monodelphis glirina)
Ihering's Three-striped Opossum (Monodelphis iheringi)
Pygmy Short-tailed Opossum (Monodelphis kunsi)
Maraj?? Short-tailed Opossum (Monodelphis maraxina)
Osgood's Short-tailed Opossum (Monodelphis osgoodi)
Hooded Red-sided Opossum (Monodelphis palliolata)
Monodelphis reigi
Peruvian Short-tailed Opossum (Monodelphis ronaldi)
Chestnut-striped Opossum (Monodelphis rubida)
Long-nosed Short-tailed Opossum (Monodelphis scalops)
Southern Red-sided Opossum (Monodelphis sorex)
Southern Three-striped Opossum (Monodelphis theresa)
Red Three-striped Opossum (Monodelphis umbristriata)
One-striped Opossum (Monodelphis unistriata)

Genus Philander
Anderson's Four-eyed Opossum (Philander andersoni)
Philander deltae
Southeastern Four-eyed Opossum (Philander frenatus)
McIlhenny's Four-eyed Opossum (Philander mcilhennyi)
Philander mondolfii
Gray Four-eyed Opossum (Philander opossum)

Genus Thylamys
Cinderella Fat-tailed Mouse Opossum (Thylamys cinderella)
Elegant Fat-tailed Mouse Opossum (Thylamys elegans)
Karimi's Fat-tailed Mouse Opossum (Thylamys karimii)
Paraguayan Fat-tailed Mouse Opossum (Thylamys macrurus)
White-bellied Fat-tailed Mouse Opossum (Thylamys pallidior)
Common Fat-tailed Mouse Opossum (Thylamys pusillus)
Argentine Fat-tailed Mouse Opossum (Thylamys sponsorius)
Tate's Fat-tailed Mouse Opossum (Thylamys tatei)
Dwarf Fat-tailed Mouse Opossum (Thylamys velutinus)
Buff-bellied Fat-tailed Mouse Opossum (Thylamys venustus)

Genus Tlacuatzin
Gray Mouse Opossum (Tlacuatzin canescens)

http://en.wikipedia.org/wiki/Opossum

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