Opossums

Didelphimorphia is the order  of common opossums of the Western Hemisphere. 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. Opossums probably diverged from the basic South American marsupials in the late Cretaceous or early Paleocene. A sister group is Paucituberculata (shrew opossums).

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 freshwater, 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.

Characteristics
Didelphimorphs are small to medium-sized marsupials, with the largest about the size of a large house cat, and the smallest the size of a mouse. 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 is: By mammal standards, this is a very full jaw. Opossums have more teeth than any other land mammal; only aquatic mammals have more. The incisors are very small, the canines large, and the molars are tricuspid.

Didelphimorphs have a plantigrade stance (feet flat on the ground) and the hind feet have an opposable digit with no claw. Like some New World monkeys, opossums have prehensile tails. The stomach is simple, with a small cecum.

Opossums have a remarkably robust immune system, and show partial or total immunity to the venom of rattlesnakes, cottonmouths, and other pit vipers. Opossums are about eight times less likely to carry rabies than wild dogs, and about one in eight hundred opossums are infected with this virus.

Reproduction and life cycle
As a marsupial, the opossum has a reproductive system that is composed of a placenta and a marsupium, which is the pouch. The young are born at a very early stage, although the gestation period is similar to many other small marsupials, at only 12 to 14 days. Once born, the offspring must find their way into the marsupium to hold onto and nurse from a teat. The species are moderately sexually dimorphic with males usually being somewhat larger than females. The largest difference between the opossum and other mammals is the bifurcated penis of the male and bifurcated vagina of the female (the source of the Latin "didelphis," meaning double-wombed). Male opossum spermatozoa exhibit cooperative methods of ensuring the survival of genotypically similar sperm by forming conjugate pairs before fertilization . Such measures come into place particularly when females copulate with multiple males. These conjugate pairs increase motility and enhance the likelihood of fertilization. Conjugate pairs dissociate into separate spermatozoa before fertilization. The opossum is one of many species that employs sperm cooperation in its reproductive life cycle.

Female opossums often give birth to very large numbers of young, most of which fail to attach to a teat, although as many as fifteen young can attach, and therefore survive, depending on species. The young are weaned between 70 and 125 days, when they detach from the teat and leave the pouch. The opossum lifespan is unusually short for a mammal of its size, usually only two to four years. Senescence is rapid.

Diet
Didelphimorphs are opportunistic omnivores with a very broad diet. Their diet mainly consists of carrion and many individual opossums are killed on the highway when scavenging for roadkill. They are also known to eat insects, frogs, birds, snakes, small mammals, and earthworms. Some of their favorite foods are fruits, and they are known to eat apples and persimmons. Their broad diet allows them to take advantage of many sources of food provided by human habitation such as unsecured food waste (garbage) and pet food.



Behavior
Opossums are usually solitary and nomadic, staying in one area as long as food and water are easily available. Some families will group together in ready-made burrows or even under houses. Though they will temporarily occupy abandoned burrows, they do not dig or put much effort into building their own. As nocturnal animals, they favor dark, secure areas. These areas may be 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. The animal will regain consciousness after a period of minutes or hours and escape.

Adult opossums do not hang from trees by their tails, though babies may dangle temporarily. Their semi-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 males) will growl deeply, raising their 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. If threatened, the baby will open its mouth and quietly hiss until the threat is gone.

Historical references
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.

Hunting, food and foodways
The opossum was once 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 available online and in books such as older editions of The Joy of Cooking. A traditional method of preparation is baking, sometimes in a pie or pasty, though at present "possum pie" most often refers to a sweet confection containing no meat of any kind. In Dominica and Trinidad opossum or "manicou" is popular and can only be hunted during certain times of the year owing to overhunting; 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.

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 (translation of Spanish article)
 * Agricola's Gracile Opossum (Cryptonanus agricolai)
 * Chacoan Gracile Opossum (Cryptonanus chacoensis)
 * Guahiba Gracile Opossum (Cryptonanus guahybae)
 * Red-bellied Gracile Opossum (Cryptonanus ignitus)
 * Unduavi Gracile Opossum (Cryptonanus unduaviensis)
 * Genus Didelphis[[Image:Opossum Skull.jpg|thumb|Skull of a [[Virginia Opossum]], D. virginiana]]
 * 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 (translation of Spanish article)
 * 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 (translation of Spanish article)
 * 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)
 * Marajó Short-tailed Opossum (Monodelphis maraxina)
 * Osgood's Short-tailed Opossum (Monodelphis osgoodi)
 * Hooded Red-sided Opossum (Monodelphis palliolata)
 * Reig's Opossum (Monodelphis reigi)
 * Ronald's 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)
 * Deltaic Four-eyed Opossum (Philander deltae)
 * Southeastern Four-eyed Opossum (Philander frenatus)
 * McIlhenny's Four-eyed Opossum (Philander mcilhennyi)
 * Mondolfi's Four-eyed Opossum (Philander mondolfii)
 * Olrog's Four-eyed Opossum (Philander olrogi)
 * Gray Four-eyed Opossum (Philander opossum)
 * Genus Thylamys (translation of Spanish article)
 * 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 (translation of Spanish article)
 * Grayish Mouse Opossum (Tlacuatzin canescens)