Didelphimorphia

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Didelphimorphia

Scientific classification
Kingdom: Animalia
Class: Mammalia
Subclass: Marsupialia
Order: Didelphimorphia
Gill, 1872
Family: Didelphidae
Gray, 1821
Genera
Several; see text
Opossum fur is quite soft, and was once commonly used in coats.
Opossum fur is quite soft, and was once commonly used in coats.

The order Didelphimorphia contains the common opossums of the western hemisphere. Opossums probably diverged from the basic South American Ameridelphian stock in the latest Cretaceous or early Paleocene. A sister group is the Paucituberculata, or shrew opossums.

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 5 incisors (four on the lower jaw), 1 canine, 3 premolars and 4 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 is moderately sexually dimorphic with males usually being somewhat larger than females.

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, opossums were intentionally introduced into the West during the Great Depression, probably as a source of food. Their range has been expanding steadily northwards, thanks in part to more plentiful, manmade sources of fresh water, and milder winters. Since 1990, their range has extended into Ontario, Canada, and they have been found as far north as 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. If you find an injured or apparently dead opossum, the best thing to do is 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 oppossums 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, though they often serve as a brace and a fifth limb when climbing. There are also confirmed accounts of the tail being used as a grip to carry bunches of leaves or bedding materials to the nest.

Classification

The members of the order are classified in one family and a genus classified as incertae sedis:

  • Incertae Sedis:
    • Genus Hyladelphys
      • Kalinowski's Opossum (Hyladelphys kalinowskii)
  • Family Didelphidae
    • Subfamily Caluromyinae
      • Genus Caluromys
        • Derby's Woolly Opossum, Caluromys derbianus
        • Equadorian Woolly Opussum, Caluromys lanatus
        • Bare-tailed Woolly Opussum, Caluromys philander
      • Genus Caluromysiops
        • Black-shouldered Opossum, Caluromysiops irrupta
    • Subfamily Glironiinae
      • 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)
        • Guahyba Gracile Opossum (Cryptonanus guahybae)
        • Red-bellied Gracile Opossum (Cryptonanus ignitus)
        • Unduavi Gracile Opossum (Cryptonanus unduaviensis)
      • Genus Didelphis
        • White-eared Opossum (Didelphis albiventris)
        • Big-eared Opossum (Didelphis aurita)
        • Guianan White-eared Opossum (Didelphis imperfecta)
        • Southern Opossum (Didelphis marsupialis)
        • Andean White-eared Opossum (Didelphis pernigra)
        • Virginia Opossum (Didelphis virginiana)
      • Genus Gracilinanus
        • Aceramarca Gracile Mouse Opossum (Gracilinanus aceramarcae)
        • Agile Gracile Mouse Opossum (Gracilinanus agilis)
        • Wood Sprite Gracile Mouse Opossum (Gracilinanus dryas)
        • Emilia's Gracile Mouse Opossum (Gracilinanus emilae)
        • Northern Gracile Mouse Opossum (Gracilinanus marica)
        • Brazilian Gracile Mouse Opossum (Gracilinanus microtarsus)
      • Genus Lestodelphys
        • Patagonian Opossum (Lestodelphys halli)
      • Genus Lutreolina
        • Lutrine Opossum or Thick-tailed Opossum (Lutreolina crassicaudata)
      • Genus Marmosa
        • Anderson's Mouse Opossum (Marmosa andersoni)
        • Grayish Mouse Opossum (Marmosa canescens)
        • Trinidad Mouse Opossum (Marmosa chapmani)
        • Little Rufous Mouse Opossum (Marmosa lepida)
        • Mexican Mouse Opossum (Marmosa mexicana)
        • Common Mouse Opossum (Marmosa murina)
        • Quichuan Mouse Opossum (Marmosa quichua)
        • Pale-bellied Mouse Opossum (Marmosa robinsoni)
        • Colombian Mouse Opossum (Marmosa ruatanica)
        • Red Mouse Opossum (Marmosa rubra)
        • Simons' Mouse Opossum (Marmosa simonsi)
        • Tyler's Mouse Opossum (Marmosa tyleriana)
        • Dryland Mouse Opossum (Marmosa xerophila)
      • Genus Marmosops
        • Bishop's Slender Opossum (Marmosops bishopi)
        • Narrow-headed Slender Opossum (Marmosops cracens)
        • Voss' Slender Opossum (Marmosops creightoni)
        • 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)
        • Bolivian Slender Opossum (Marmosops ocellatus)
        • Brazilian Slender Opossum (Marmosops paulensis)
        • Delicate Slender Opossum (Marmosops parvidens)
        • Pinheiro's Slender Opossum (Marmosops pinheiroi)
      • Genus Metachirus
        • Brown Four-eyed Opossum (Metachirus myosuros)
        • Guianan Brown Four-eyed Opossum (Metachirus nudicaudatus)
      • Genus Micoureus
        • Alston's Mouse Opossum (Micoureus alstoni)
        • Pale-bellied Woolly Mouse Opossum (Micoureus constantiae)
        • Woolly Mouse Opossum (Micoureus demerarae)
        • Tate's Woolly Mouse Opossum (Micoureus paraguayana)
        • 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)
        • Marajó Short-tailed Opossum (Monodelphis maraxina)
        • Osgood's Short-tailed Opossum (Monodelphis osgoodi)
        • Hooded Red-sided Opossum (Monodelphis palliolata)
        • 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
        • Black Four-eyed Opossum (Philander andersoni)
        • Southeastern Four-eyed Opossum (Philander frenata)
        • McIlhenny's Four-eyed Opossum (Philander mcilhennyi)
        • 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)