Karimi's fat-tailed mouse opossum (Thylamys karimii)

Karimi's fat-tailed mouse opossum
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Karimi's fat-tailed mouse opossum fact file

Karimi's fat-tailed mouse opossum description

GenusThylamys (1)

Karimi’s fat-tailed mouse opossum (Thylamys karimii) is a South American marsupial named for its short tail, which becomes seasonally thickened through the storage of fat (3).

The relatively unknown Karimi’s fat-tailed mouse opossum has greyish or greyish-brown fur on the upperparts, and pure white underparts (4). A dark ring surrounds each prominent eye, and the small paws bear stout claws (5).
The male and the female Karimi’s fat-tailed mouse opossum differ slightly in appearance, with the female typically being smaller than the male and having a yellow tinge to the white throat (3).
Karimi’s fat-tailed mouse opossum largely resembles the better-known dwarf fat-tailed mouse opossum (Thylamys velutinus) (6). However, unlike the other opossums in its genus, the tail of Karimi’s fat-tailed mouse opossum is not prehensile (6).
Head-body length: c. 9.5 cm (2)
Tail length: c. 7.2 cm (2)

Karimi's fat-tailed mouse opossum biology

Compared to other opossum species, there is relatively little known about Karimi’s fat-tailed mouse opossum. It is known to be a fairly terrestrial animal, which tends to stay down at the lower levels of vegetation (6). As a result, it is not as adapted for climbing trees and lacks the prehensile tail of other opossum species. Instead, the tail of Karimi’s fat-tailed mouse opossum can become swollen as it acts as a store of fat (3).

Although the diet of this species is not known, it is likely to be similar to other mouse opossums, which feed on insects, fruit and small vertebrates (5).

Like other mouse opossums, it is possible that the Karimi’s fat-tailed mouse opossum breeds from September to March, during which time the female may have two litters (5). Mouse opossums, like all marsupials, have a short gestation period, and the young are poorly developed at birth and crawl immediately to the female’s teats (7). Although each litter can contain as many as 15 young (5), many will die as the female produces more young than she has mammae (7).

Most development takes place as the young feed on the female's milk (7). The length of time that the female Karimi’s fat-tailed mouse opossum feeds the young for is not known, but like other mouse opossums it is likely to be more than 68 days (7). Unlike most other marsupials, the Karimi’s fat-tailed mouse opossum lacks a pouch in which the young are protected as they feed (3).


Karimi's fat-tailed mouse opossum range

Karimi’s fat-tailed mouse opossum occurs only in Brazil. It is widely distributed within the two major biomes in Brazil, the cerrado and the caatinga, in the northeast and central parts of the country (1) (3).


Karimi's fat-tailed mouse opossum habitat

Karimi’s fat-tailed mouse opossum is known to inhabit dry, open vegetated regions at elevations between 300 and 1,100 metres above sea level (6). The two main regions where it is found are the dry caatinga forest and the dense savannah of the cerrado (1).


Karimi's fat-tailed mouse opossum status

Karimi’s fat-tailed mouse opossum is classified as Vulnerable (VU) on the IUCN Red List (1).

IUCN Red List species status – Vulnerable


Karimi's fat-tailed mouse opossum threats

Even though Karimi’s fat-tailed mouse opossum is widely distributed in Brazil, it occurs in low densities and is threatened by habitat loss (1).

The open habitats occupied by Karimi’s fat-tailed mouse opossum are being converted for large-scale farming, in particular for soybean plantations (1)


Karimi's fat-tailed mouse opossum conservation

There are currently no specific conservation measures in place for Karimi’s fat-tailed mouse opossum, but it reportedly occurs within a number of protected areas(1), which should offer this species some protection.

Karimi’s fat-tailed mouse opossum is also likely to benefit from the work of organisations such as WWF, which are working with farmers to identify how the negative environmental impacts of soybean production can be reduced (8).


Find out more

Learn more about soybean production and conservation:

Find out about conservation in Brazil:



This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact:

This species information was authored as part of the Arkive and Universities Scheme.


Large, naturally occurring biological communities, such as forest or desert.
A particular type of habitat of north-eastern Brazil defined by small thorny trees and shrubs.
A vast, tropical woodland-savanna ecosystem of Brazil, the most extensive of its type in South America. Comprising around 21 percent of Brazil’s total land area, the cerrado includes savanna, woodland-savanna and dry forest ecosystems, and has a pronounced dry season.
A category used in taxonomy, which is below ‘family’ and above ‘species’. A genus tends to contain species that have characteristics in common. The genus forms the first part of a ‘binomial’ Latin species name; the second part is the specific name.
The state of being pregnant; the period from conception to birth.
The organs of females that produce milk. Also known as mammary glands.
A diverse group of mammals characterised by their reproduction, in which gestation is very short, and the female typically has a pouch (marsupium) in which the young are raised. When born, the tiny young crawls to the mother’s teats, where it attaches and stays for a variable amount of time, whilst it continues to develop. Marsupials also differ from placental mammals in their dentition.
Capable of grasping.
An animal with a backbone, including mammals, birds, reptiles, amphibians and fish.


  1. IUCN Red List (November, 2011)
  2. Eisenberg, J.F. and Redford, K.H. (1999) Mammals of the Neotropics: The Central Neotropics: Ecuador, Peru, Bolivia, Brazil. University of Chicago Press, Chicago.
  3. Carmignotto, A.P. and Monfort, T. (2006) Taxonomy and distribution of the Brazilian species of Thylamys (Didelphimorphia: Didelphidae). Mammalia, 70: 126-144.
  4. Gardner, A.L. (2008) Mammals of South America. Volume 1: Marsupials, Xenarthrans, Shrews, and Bats. University of Chicago Press, Chicago.
  5. Nowak, R.M. (1999) Walker’s Mammals of the World. The Johns Hopkins University Press, Baltimore.
  6. Carvhallo, B. de A., Oliveira, L.F.B. and Mattevi, M.S. (2009) Phylogeny of Thylamys (Didelphimorphia, Didelphidae) species, with special reference to Thylamys karimii. Iheringia Série Zoologia, 99: 419-425.
  7. MacDonald, D.W. (2006) The Encyclopedia of Mammals. Oxford University Press, Oxford.
  8. WWF – Brazil (November, 2011)

Image credit

Karimi's fat-tailed mouse opossum  
Karimi's fat-tailed mouse opossum

© Mauro Teixeira Jr.

Mauro Teixeira Jr.


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