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Opossums probably diverged from the basic South American marsupials in the late Cretaceous or early Paleocene. A sister group is the Paucituberculata, or shrew opossums. They are commonly also called "possums", though that term is more correctly applied to Australian fauna of the suborder Phalangeriformes. When this article refers to Opossums, it is refering to opposums of the Western Hemisphere.


Just the Facts: Opossums 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.



Not So Picky Eaters: Opossums 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, man-made sources of fresh water, increased shelter from urban encroachment, and milder winters. Their range has extended into Ontario, Canada, and they have been found as far north as Toronto.


Playing Possum: 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.


Champion Immune Systems: Opossums have a remarkably robust immune system, and show partial or total immunity to the venom of rattlesnakes, cottonmouths, and other pit vipers. Thanks to their lower blood temperature, rabies is almost unknown in opossums.



 Kingdom: Animalia

 Phylum: Chordata

 Class: Mammalia

 Infraclass: Marsupialia

 Order: Didelphimorphia

 Family: Didelphidae