Diversity of the

American Marsupials


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Introduction

Order: Didelphimorphia

Within this order are 2 families, with 95 species across 19 genera, and consisting of the 'common opossums', the sister-group to some or all of the Australian marsupials. One of these 2 families is arboreal, the other less so. This order was the first to be discovered and classified following the discovery of the Americas in the 15th century.

Didelphimorphia (5K)
Virginia Opossum, Didelphis virginiana

The diversification of this order occurred in South America during the late Cretaceous and early Palaeocene, with North and Central American species migrating North during the Great Panaman Interchange. There was a net loss of didelphimorphians in the Oligocene following this event, but the diversity of the order increased again during the mid to late Cainozoic. Representatives of this order are the most similar to the earliest known fossil marsupials.

Species in this order range in size from that of a mouse to a large cat, usually with a long snout, a 'full' mammal jaw with small incisors and large canines, a narrow braincase and a prehensile tail used as a 5th limb and brace when climbing. This tail is not used to hold the individuals adult weight on its' own as it is not strong enough, unlike other non-marsupial mammalian species with a prehensile tail. Didelphimorphians are nocturnal, usually solitary, sexually dimorphic with males generally larger than females, and have a robust immune system. Members of this order have a flexible and diverse diet, with species with carnivorous, insectivorous and herbivorous diets known.

An unusual feature of the didelphimorphians is the ability to 'play possum', where they mimic the appearance and smell of a sick or dead animal when threatened to avoid predators. This is a completely involuntary physiological response and is not a conscious decision on the individuals part, and leaves the creature in a catatonic state until it wakes.

Order: Paucituberculata.

Order: Microbiotheria.

Order: Sparassodonta.

Order: Groeberida.

Order: Argyrolagida.