Opossum

For the Eastern Hemisphere marsupial, see possum.
For other uses of "Opossum", see Opossum (disambiguation).
Didelphidae[1]
Temporal range: Early Miocene–Recent

[2]

Virginia opossum (Didelphis virginiana)
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Infraclass: Marsupialia
Superorder: Ameridelphia
Order: Didelphimorphia
Gill, 1872
Family: Didelphidae
Gray, 1821
Genera

Several; see text

The opossums, also known by their scientific name Didelphimorphia /dˌdɛlfˈmɔːrfiə/), make up the largest order of marsupials in the Western Hemisphere, including 103 or more species in 19 genera. Of South American ancestry, they entered North America following the connection of the two continents. Their unspecialized biology, flexible diet, and reproductive habits make them successful colonizers and survivors in diverse locations and conditions.

Etymology

The word "opossum" is borrowed from the Virginia Algonquian (Powhatan) language, and was first recorded between 1607 and 1611 by the Jamestown colonists John Smith (as "opassom") and William Strachey (as "aposoum").[3] The word ultimately derives from the Proto-Algonquian word *wa˙p- aʔθemw, meaning "white dog" or "white beast/animal".

They are also commonly called possums, particularly in the Southern United States and Midwest. Following the discovery of Australia, the term "possum" was borrowed to describe distantly related Australian marsupials of the suborder Phalangeriformes.[4]

Characteristics

Skeleton of the gray short-tailed opossum (Monodelphis domestica)

Didelphimorphs are small to medium-sized marsupials, ranging in size from a large house cat to 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: 5.1.3.44.1.3.4. By mammalian standards, this is an unusually 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. Notably, the male opossum has a forked penis bearing twin glandes.[5]

Opossums have a remarkably robust immune system, and show partial or total immunity to the venom of rattlesnakes, cottonmouths, and other pit vipers.[6][7] Opossums are about eight times less likely to carry rabies than wild dogs, and about one in eight hundred opossums is infected with this virus.[8]

Although all living opossums are essentially opportunistic omnivores, different species vary in the amount of meat and vegetation they include in their diet. Members of the Caluromyinae are essentially frugivorous; whereas the lutrine opossum and Patagonian opossum primarily feed on other animals.[9] The yapok (Chironectes minimus) is particularly unusual, as it is the only living semi-aquatic marsupial, using its webbed hindlimbs to dive in search of freshwater mollusks and crayfish.[10] Most opossums are scansorial, well-adapted to life in the trees or on the ground, but members of the Caluromyinae and Glironiinae are primarily arboreal, whereas species of Metachirus, Monodelphis, and to a lesser degree Didelphis show adaptations for life on the ground.[11]

Reproduction and life cycle

Further information: Marsupial#Reproductive system
Sleeping Virginia opossum with babies in her relaxed pouch

As a marsupial, the opossum has a reproductive system including a divided uterus and marsupium, which is the pouch.[12] The average estrous cycle of the opossum is about 28 days.[13] Opossums do possess a placenta,[14] but it is short-lived, simple in structure, and, unlike that of placental mammals, is not fully functional.[15] 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.[16] Once born, the offspring must find their way into the marsupium to hold on to and nurse from a teat.

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,[17] 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.[18]

The species are moderately sexually dimorphic with males usually being slightly larger, much heavier, and having larger canines than females.[17] The largest difference between the opossum and non-marsupial mammals is the bifurcated penis of the male and bifurcated vagina of the female (the source of the term "didelphimorph," from the Greek "didelphys," meaning double-wombed).[19] Opossum spermatozoa exhibit sperm-pairing, forming conjugate pairs in the epididymis. This may ensure that flagella movement can be accurately coordinated for maximal motility. Conjugate pairs dissociate into separate spermatozoa before fertilization.[20]

Behavior

A Virginia opossum inhabiting a piano in Houston, Texas, shortly before its release
An opossum "playing dead"

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.

Juvenile opossum hissing defensively.

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 an opossum is "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. The 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 that begins with slight twitching of the ears.[21]

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.

Biochemistry

Opossums are remarkably resistant to snake venom, ricin, and botulinum.[7]

Habitat

Opossums can be found from Meso America to North America, but are considered an invasive species in places such as Southern Ontario and British Columbia.[22]

In hunting and foodways

The Virginia opossum was once widely hunted and consumed in the United States.[23][24][25]

In Dominica, Grenada, and Trinidad the common 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. 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 northern/central Mexico, opossums are known as "tlacuache" or "tlacuatzin". Their tails are eaten as a folk remedy to improve fertility.[26] In the Yucatán peninsula they are known in the Yucatec Mayan language as "och"[27] and they are not considered part of the regular diet by mayan people, but still considered edible in times of famine.

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

The range of Didelphis virginiana across North America in green

Classification based on Voss and Jansa (2009)[28]

References

  1. Gardner, A. (2005). Wilson, D.E.; Reeder, D.M., eds. Mammal Species of the World: A Taxonomic and Geographic Reference (3rd ed.). Johns Hopkins University Press. pp. 3–18. ISBN 978-0-8018-8221-0. OCLC 62265494.
  2. Francisco Goin; Alejandra Abello; Eduardo Bellosi; Richard Kay; Richard Madden; Alfredo Carlini (2007). "Los Metatheria sudamericanos de comienzos del Neógeno (Mioceno Temprano, Edad-mamífero Colhuehuapense). Parte I: Introducción, Didelphimorphia y Sparassodonta". Ameghiniana 44 (1): 29–71.
  3. Mithun, Marianne (2001). The Languages of Native North America. Cambridge University Press. p. 332. ISBN 0-521-29875-X.
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  5. Krause, William J.; Krause, Winifred A. (2006).The Opossum: Its Amazing Story. Department of Pathology and Anatomical Sciences, School of Medicine, University of Missouri, Columbia, Missouri. p. 39
  6. "The Opossum: Our Marvelous Marsupial, The Social Loner". Wildlife Rescue League.
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