There are some 250 species of living marsupials in the world and more than 150 fossil species are known. South American didelphoids radiated widely as carnivores and omnivores and some species in the past reached the size of a panther, e.g. Prothylacynus and the sabertooth, Thylacosmilus atrox, which was remarkably similar to the sabertoothed feline, Eusmilus and Smilodon, which had enormously enlarged canines.
Some of the Australian marsupials reached the size of a rhinoceros, such as Diprotodon australis, which became extinct in late Pleistocene. The present American marsupials are a small of a highly diversified group that existed in Pleistocene epoch. There are two families, Didelphidae containing 12 genera and Coenolestidae comprising three genera.
1. Didelphis. The genus contains three species, namely, the Virginia opossum, D. virginiana found in the central and North America and the black-eared opossum, D. marsupialis and the white-eared opossum, D. albiventris which are found in temperate South America. All the species have well-developed pouches. The genus ranges from Ontario in Canada to as far south as Argentina, inhabiting temperate wooded areas but now has spread to arid areas of Arizona as well. They are half to one metre in length, omnivorous, adept climbers and show extremely adaptable behaviour.
2. Philander. It has only one species, the grey four-eyed opossum, P. opossum, which is pouched with furry tail and is found throughout the central and South America, from Mexico to Brazil and Argentina. Primarily terrestrial, they are good climbers and swimmers and are omnivorous, feeding on small mammals, birds, eggs and fruits. They measure 50-60 cm in length, with brown or grey colour and distinct white spots above the eyes.
3. Metachirus. Half a metre long M. nudicaudatus is sometimes called “brown four-eyed opossum” because it has reddish-brown fur with two light spots above each eye. Marsupium is replaced by lateral folds of skin and tail is hairless. It is distributed from Nicaragua to northern Argentina, living in lowland forests where it primarily feeds on fruits and sometimes on insects and eggs. It is strictly nocturnal, arboreal and terrestrial, nesting on tree branches.
4. Lutreolina. The pouchless, reddish, weasel-like Lutrine opossum, L. crassicaudata is adapted to aquatic mode of life and ranges from the savannas of eastern Colombia to Argentina. They are nocturnal, good swimmers and inhabit many types of habitats from forests to open grasslands where they feed on small rodents, fishes, insects and seeds. Body measures up to 40 cm long, without a prehensile tail, although they are good climbers.
5. Chironectes. Water opossum or Yapock, C. minimus is aquatic, living in small streams and ponds and ranges from Mexico to northeastern Argentina. It is 45-70 cm long, dark grey with light bands and patches, webbed hind feet, laterally compressed tail and well developed pouch. It is predominantly carnivorous, feeding on insects, shrimps, fish, frogs and fruits.
6. Marmosa. Commonly called Murine or mouse opossum, this is the largest genus comprising 50 species that range through Mexico to all of South America. The North American species are: M. mexicana, M. invicta and M. canescens while the important South American species are M. robinsoni, M. fuscata, M. cinerea, M. karimii, M. tatei, M. andersoni, M. elegans, M. Formosa. The size ranges from 10 to 21 cm. They are omnivorous, pouchless and have a prehensile tail.
7. Monodelphis. This is a diverse genus of short-tailed brownish opossums, having 11 species found from eastern Panama to central Argentina. The species comprise M. adusta, M. orinoci, M. brevicaudata, M. dimidiate. They are terrestrial and climb well, preferring to live near water and often found near human habitations. Size varies from 15 to 20 cm and pouch is absent and the tail is not prehensile. Mammary glands number up to 27.
8. Lestodelphys. The Pentagonian opossum, L. halli is one of the rarest of marsupials found only in coastal areas of Pentagonia. It is nocturnal, terrestrial and arboreal and cold adapted, carnivorous, 10 cm long, with a heavily furred tail.
9. Caluromys. There are three species of Woolly opossum, having luxuriant orange and grey fur. The pouched C. derbianus is found in Central and South America and C. lanatus on the eastern side of Andes and the Amazon basin. The smaller and pouchless species, the bare-tailed woolly opossum, C. philander is found in northeastern side of South America. Their size varies between 27 to 50 cm length. They are very agile and more arboreal than terrestrial, generally dark brown in colour with dark stripes on face and a prehensile tail that is furred at the basal half. Marsupium is sometimes present and sometimes replaced by lateral folds of skin.
10. Caluromysiops. The single species, Black-shouldered opossum, C. irrupta has rounded head and waxy yellow ears and is restricted to Peru where it is adapted to tropical wet forests. Body colour is light grey with black stripe on shoulder region and light face. Tail is hairy and body is 40-50 cm long. It is nocturnal and arboreal in habit.
11. Glironia. Two species having furred tails, G. venusta and G. criniger are rare, found in the rain forests of Ecuador, Peru and Bolivia. They live in dense humid forests, living arboreal and nocturnal life. Small in size, they measure 16-20 cm in length and their diet comprised insects, fruits and seeds.
12. Dromiciops. Only one species commonly called Monitos del Monte, D. australis is found in southern Chile and Argentina. It is arboreal with a prehensile tail, inhabiting dense, humid forests. Small body size measures only 12 cm, with brown fur having grey patches. Females have a small pouch with 5 mammary glands.
They lack pouch, are insectivorous and prefer densely vegetated, humid habitat. Their general appearance is like a shrew with elongated rostrum.
1. Caenolestes. There are 5 species, C. fuliginosus is found in Peru, the black coloured, C. convelatus found in Quito and C. obscurus in Colombia. They are primarily terrestrial, crepuscular or nocturnal, living in damp and cool zones. The rare C. tatei and C. caniventer are found at lower altitudes where they are adapted to higher temperatures.
2. Lestoros. The single species, L. inca found in Peru has small canine and is rare. It has elongated rostrum and small eyes and adapted to high mountains, above 2800 metres. Their size is 20-27 cm. They are terrestrial and nocturnal and feed on insects and small invertebrates.
3. Rhyncholestes. The single species, R. raphanurus is found in Chile. The male has large canines and both sexes have double cusped upper incisors and fatty tail. It has elongated head, small eyes and small body size, measuring 18 to 22 cm in length, dark brown in colour, terrestrial and nocturnal in habit. Females have no pouch but 5 mammary glands.