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Opossum

Didelphidae
Opossum (Didelphidae)

Scientific Classification

  • Kingdom Animalia
  • Phylum Chordata
  • Class Mammalia
  • Infraclass Marsupialia
  • Superorder Ameridelphia
  • Order Didelphimorphia
  • Family Didelphidae

Opossums are small to medium-sized, semi-arboreal, pouched mammals recognized by their grayish fur, a prominent median brain ridge (sagittal crest), a narrow braincase, and a long snout. They constitute the family Didelphidae, under the largest order of marsupials in the Western Hemisphere, Didelphimorphia. It is believed that these animals originated in South America and later moved to North America with the formation of the Isthmus of Panama around 3 million years ago. 

Opossum (Didelphidae)

Scientific Classification

  • Kingdom Animalia
  • Phylum Chordata
  • Class Mammalia
  • Infraclass Marsupialia
  • Superorder Ameridelphia
  • Order Didelphimorphia
  • Family Didelphidae

Currently, 126 species of opossums are found in North, Central, and South America, with only one species, the Virginia opossum, residing in the United States and Canada. This species is often referred to as possums in North America, though it is different from the Australasian marsupials of the order Diprotodontia, actually known by the same name.

Description

Size

Opossums are about 2.5 ft (76 cm) in length (from nose to tail) and weigh around 8.8 to 13.2 lb (4 to 6 kg). The largest extant species, the Virginia opossum (Didelphis virginiana), reaches up to 3.5 ft (109 cm) in body length.

They exhibit sexual dimorphism, with the males being slightly larger than the females.

Body Plan

These animals have long and pointed snouts, a narrow braincase, and a distinct bony ridge running along the midline of the braincase called the sagittal crest. Their bodies are covered in woolly or fine fur, ranging from pale gray to yellow-brown in color, with many having a dark facial mask encircling their eyes.

As marsupials, large opossum species have a pouch for carrying and nursing their babies, while smaller species simply possess lateral abdominal folds. Their tails are usually long, hairless, and prehensile, allowing them to grip and hang from tree branches.

Dentition

They have a total of 50 teeth with a dental formula of (5.1.3.4/4.1.3.4)× 2 = 50. The incisors are small, the canines are large, and the molars have three prominent cusps (tricuspid).

Taxonomy

The term opossum derives from the Powhatan language, which, in turn, has its roots in a  Proto-Algonquian word, meaning ‘white dog or dog-like beast.’ This animal was first recorded by John Smith (as opassom) and William Strachey (as aposoum) in 1607 and 1611.

The Virginia opossum, the only species in the United States and Canada, is often referred to as possums regionally. However, as Europeans migrated to Australia, they borrowed this name and used it for the distantly related Australian marsupials of the suborder Phalangeriformes.

The 4 subfamilies and 18 genera housing 126 species of opossums are listed below:

Opossum (Didelphidae)

Evolution and Fossil Records

Although these marsupials are called living fossils, the earliest opossum fossils belong to the Early Miocene Epoch (around 20 million years ago). The last common ancestor (LCA) of all extant opossums dates back to around 23 million years ago, during the Oligocene-Miocene boundary.

They are believed to have originated in the Amazon rainforests (Amazonia region) of northern South America and started to diversify there around the Late Miocene Epoch. Initially, the niches currently occupied by opossums in South America belonged to other mammalian groups, like paucituberculatans and sparassodonts. However, with time, Large American opossums (Didelphis) gradually increased in size, and the diversity of those groups slowly declined. Meanwhile, other opossum genera like Thylophorops, Thylatheridium, and Hyperdidelphys flourished around the Late Miocene-Pliocene boundary.

Later, with the formation of the Isthmus of Panama (around 3 million years ago), opossums moved to North America through the Great American Interchange.

Distribution and Habitat

These marsupials are found in North, South, and Central America. The Virginia opossum, the only species found in Canada and the United States, ranges from south Canada to Nicaragua and Honduras.

Although they typically inhabit swamps and forests receiving abundant rainfall, these mammals are highly adaptable and are also spotted in urban areas. The Virginia opossum is mostly found in wooded areas.

Opossums usually prefer nesting in tree holes or dens made by other animals, but they are also frequently found living in abandoned burrows, sheds, barns, and under homes.

Diet

These animals are opportunistic omnivores that feed on insects, snails, rodents, frogs, and birds, like chickens. It is estimated that a single species of Virginia opossum consumes about 5,000 ticks per year. 

They also consume plants, fruits, and grain, besides scavenging on skeletal remains of animals and other detritus obtained from garbage cans and dumpsters. 

For example, members of the subfamily Caluromyinae are frugivorous, feeding exclusively on fruits, while those of the tribe Didelphini, being immune to snake venom, often feed on rattlesnakes and pit vipers. In contrast, water opossums exclusively feed on freshwater mollusks and crayfish.

Behavior

They are primarily solitary animals that forage at night (nocturnal) and rest during the day in hollow tree trunks, rock crevices, or burrows. However, they gather during the brewing season, and females are often found to accompany their young. 

Opossums remain active throughout the year and are not known to hibernate in winter. They are nomadic, roaming about till they find a suitable shelter. To do so, they follow ready-made trails created by animals or humans and rely on culverts to cross highways safely.

Locomotion

Most opossums are scansorial and climb trees using the grip of their claws. Members of the subfamilies Caluromyinae and Glironiinae are primarily arboreal, mostly resting in trees, while members of the genera Metachirus, Monodelphis, and Didelphis mostly walk on the ground. Such walking is plantigrade, in which the toes and metatarsals fall flat on the ground.

Species with prehensile tails, such as the Virginia opossum, often use them as a fifth limb for climbing trees.

Defense

Though generally harmless, opossums, especially males, respond to threats by growling deeply, hissing, or even belching. Females, on the other hand, often bite their predators if their babies are under target.

When none of the above reactions are enough to ward off enemies, they ‘play possum.’ In this behavior, an opossum flops onto its side, stiffens its body as if unconscious, curls up with half-closed eyes, and bares its teeth. It also pulls back its lips, drools, and releases a foul-smelling secretion from its anal glands. Such an act presents the opossum as a dead animal, thereby preventing the predator from pursuing it. They remain in this state of stupor for a few minutes or even hours, after which the opossums wake up with a slight twitching of the ears.

Communication

Although opossums are not generally noisy, they often emit distinct sounds, like chirps, hisses, clicks, and screams. They are sensitive to high-frequency sounds, typically ranging between 8 to 64 kHz.

Lifespan

Opossums have a surprisingly short lifespan for a mammal of their size. In the wild, they barely live for 1 to 2 years, while in captivity, they survive for 4 years or even more.

Reproduction and Life Cycle

During the mating season, usually between January and July, male opossums attract their female mates through auditory and olfactory signals. They emit clicking sounds with their mouth and also produce a musky-odored fluid from specialized sternal scent glands. They often stain their chests yellow with this fluid and smack their mouths to draw the attention of the females.

After a short gestation period of about 12 to 14 days, the female gives birth to up to 20 (typically 8) honeybee-sized young (joeys) per litter. These young are born at a very early stage since the placenta in opossums, unlike those of placental mammals, is short-lived and only partially functional. The young hurriedly find their way to the marsupium, if present, and latch to a teat. 

Though opossums give birth to a number of young, only 13 offspring can survive. The joeys remained latched onto their mothers for about 50 to 70 days and are usually weaned by 125 days. When the young get separated, they make a sneezing sound to alert their mothers, who, in turn, reciprocate with clicking sounds and wait for their babies. The young attain sexual maturity at about 6 to 8 months of age.

Predators

They are preyed upon by dogs, bobcats, coyotes, red foxes, raccoons, owls, and large snakes. Humans also hunt opossums to consume their meat.

Ecological Importance

As scavengers, opossums help keep the environment clean by consuming carrion, thereby preventing the spread of diseases. Additionally, they are natural pest controllers, feeding on populations of rodents, ticks, snails, and slugs.

References Article last updated on 20th November 2024

References -

  1. Opossum: Wikipedia.org
  2. Opossum: Sandiegozoo.org
  3. Opossums: Wa.gov
  4. Opossums: Nationalgeographic.com
  5. General Opossum Information: Opossumsocietyus.org
  6. Opossums: Paws.org
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