Opossum

Opossums (Didelphimorphia, ) make up the largest order of marsupials in the Western Hemisphere, including 103 or more species in 19 genera. They are also commonly called possums, though that term technically refers to Australian fauna of the suborder Phalangeriformes. The Virginia opossum was the first animal to be named an opossum; usage of the name was published in 1610. The word opossum comes from the Proto-Algonquian aposoum, pronounced *wa˙p- aʔθemw, meaning "white dog" or "white beast/ animal". Opossums probably diverged from the basic South American marsupials in the late Cretaceous or early Paleocene.

Their unspecialized biology, flexible diet and reproductive strategy make them successful colonizers and survivors in diverse locations and conditions.

Characteristics
Didelphimorphs are small to medium-sized marsupials, with the largest just exceeding the size of a large house cat, and the smallest the size of a small 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 mammalian standards, this is a very full jaw. 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. Like all marsupials, the fur consists of awn hair only, and the females have a pouch. The tail and parts of the feet bear scutes. 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 including a divided uterus and marsupium, which is the pouch. Opossums do possess a placenta, but it is short-lived, simple in structure, and, unlike that of placental mammals, is not fully functional. The young are therefore 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 slightly larger, much heavier, and having larger canines 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). Opossum spermatozoa exhibit sperm-pairing, forming conjugate pairs in the epidydimis. This may ensure that flagella movement can be accurately coordinated for maximal motility. Conjugate pairs dissociate into separate spermatozoa before fertilization.

Female opossums often give birth to very large numbers of young, most of which fail to attach to a teat, although as many as thirteen 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, slugs, and earthworms. Some of their favorite foods are fruits, and they are known to eat avocados, apples, clementines, 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. This physiological response is involuntary (like fainting), rather than a conscious act. In the case of baby opossums, however, the brain does not always react this way at the appropriate moment, and therefore they often fail to "play dead" when threatened. When "playing possum", the animal's lips are drawn back, the teeth are bared, saliva foams around the mouth, the eyes, close or half-close, and a foul-smelling fluid is secreted from the anal glands. Their stiff, curled form can be prodded, turned over, and even carried away without reaction. The animal will typically regain consciousness after a period of between 40 minutes and 4 hours, a process which begins with slight twitchings of the ears.

Adult opossums do not hang from trees by their tails, as sometimes depicted, 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.

Hissing or squawking is a defensive process that helps the opossum deter other animals from approaching it.

In hunting and foodways
The Virginia Opossum was once widely hunted and consumed in the United States where available.

In Dominica and Trinidad the Common Opossum or manicou is popular and can only be hunted during certain times of the year owing to over-hunting. The meat is traditionally prepared by smoking, then stewing. It 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. Historically, hunters in the Caribbean would place a barrel with fresh or rotten fruit to attract opossums that would feed on the fruit or insects.

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.

Opossum pelts have long been part of the fur trade.

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) † 1962
 * 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)
 * Isthmian Mouse Opossum (Marmosa isthmica)
 * 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)
 * Marmosa simonsi
 * Tyleria Mouse Opossum (Marmosa tyleriana)
 * Guajira Mouse Opossum (Marmosa xerophila)
 * Marmosa zeledoni
 * Genus Marmosops
 * Bishop's Slender Opossum (Marmosops bishopi)
 * Narrow-headed Slender Opossum (Marmosops cracens)
 * Creighton's slender opossum 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)Monodelphis domestica93-300.jpg
 * 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)