White-bellied fat-tailed mouse opossum

White-bellied fat-tailed mouse opossum
Conservation status
Least Concern  (IUCN 3.1)
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Didelphimorphia
Family:	Didelphidae
Genus:	Thylamys
Species:	T. pallidior
Binomial name
Thylamys pallidior (Thomas, 1902)
White-bellied fat-tailed mouse opossum range

The white-bellied fat-tailed mouse opossum (Thylamys pallidior) is a species of opossum in the family Didelphidae. It is found in Argentina, Bolivia, Chile and Peru.

Description

The white-bellied fat-tailed mouse opossum is a small, mouse-like marsupial, with large ears and a narrow, pointed snout. The head and body are from 73 to 105 millimetres (2.9 to 4.1 in) in total length, and the tail is slightly longer, ranging from 90 to 115 millimetres (3.5 to 4.5 in). Adults weigh between 13 and 39 grams (0.46 and 1.38 oz).

The fur on the upper parts of the animal is light cinnamon brown, while that on the underside is white or creamy, with a relatively sharp line dividing the two colors. The fur on the face is generally paler than that on the upper parts, with rings of darker, almost black, fur surrounding each eye, and stretching towards the nose. The tail is prehensile, with only sparse hairs, albeit in a similar color to those on the body. The tail becomes noticeably thicker, especially at the base, during the autumn, when the animal lays down fat reserves in preparation for winter. The fur on the feet is white, and relatively dense about the ankles.

Distribution and habitat

The white-bellied fat-tailed mouse opossum is found in southern Peru and south-western Bolivia, in the northernmost regions of Chile, and along the eastern slopes of the Andes mountains in western and central Argentina. It inhabits arid and semi-arid environments from sea level to 4,500 metres (14,800 ft), ranging from the coastal deserts of Peru, through the Andes and the Monte Desert, and into the Patagonian steppe of Argentina. It generally inhabits rocky environments with little plant cover, but can be found in dry forest or thorn scrub.

There are no recognised subspecies.

Behavior

White-bellied fat-tailed mouse opossums are nocturnal animals with good climbing abilities, although they prefer to spend most of their time on the ground. They nest in natural cavities, either in trees or shrubs, or beneath rocks. Although they do not truly hibernate through the winter, they do enter torpor if temperatures fall below around 15 °C, and therefore may be inactive through much of the winter period.

In the wild, they rarely drink, being able to subsist on the water in their food. They eat a wide range of insects and spiders, but prefer beetles, of which they may eat up to twenty a night. Although such small invertebrates compose the majority of their diet, they also eat a moderate amount of leaves and seeds, and will occasionally consume small vertebrates such as mice and lizards. Their main predators include the barn owl and the Magellanic horned owl.

Reproduction

White-bellied fat-tailed mouse opossums are believed to be able to breed up to three times a year, although most probably only give birth once or twice. The young are born in litters of up to fifteen individuals, typically during the summer months. Unlike some other marsupials, the females do not have a pouch; the teats are variable in both number and arrangement, and may not all be functional at the same time. Individuals have lived up to eighteen months in captivity.

Evolution

It is closely related to T. karimii. However, phylogenetic analysis shows that the species' closest relatives are probably the elegant, common, and Tate's fat-tailed mouse opossums, all of which also inhabit arid environments. Although fossils are known only from the Holocene, estimates for the divergence of the species from its closest relatives range from 2.2 to 6 million years ago.