page_title: Opossum
section_title: Characteristics
hierarchical_section_title: Opossum / Characteristics
caption_attribution_description: English: Skeleton of Monodelphis domestica. Scale bar is 1 cm.
context_page_description: The opossum is a marsupial of the order Didelphimorphia endemic to the Americas. The largest order of marsupials in the Western Hemisphere, it comprises 103 or more species in 19 genera. Opossums originated in South America and entered North America in the Great American Interchange 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.
  In the United States and Canada, the only species found is the Virginia opossum. It is usually simply referred to as an "opossum" but some regional dialects shorten this further to "possum", which should not be confused with the Australasian arboreal marsupials of suborder Phalangeriformes that are also called "possums" because of their resemblance to the Didelphimorphia.
context_section_description: Didelphimorphs are small to medium-sized marsupials that grow to the size of a house cat. They tend to be semi-arboreal omnivores, although there are many exceptions. Most members of this order have long snouts, a narrow braincase, and a prominent sagittal crest. The dental formula is:  × 2 = 50 teeth. 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 that of 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. Like most marsupials, the male opossum has a forked penis bearing twin glandes.
  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. The water opossum or 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. The extinct Thylophorops, the largest known opossum at 4–7 kg, was a macropredator. 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. Metachirus nudicaudatus, found in the upper Amazon basin, consumes fruit seeds, small vertebrate creatures like birds and reptiles and invertebrates like crayfish and snails, but seems to be mainly insectivorous.
caption: Skeleton of the gray short-tailed opossum (Monodelphis domestica)
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