Anderson’s mouse opossum (Marmosa andersoni)

Head of the holotype specimen of the Anderson's mouse opossum
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Anderson’s mouse opossum fact file

Anderson’s mouse opossum description

GenusMarmosa (1)

Only seven individuals of this small marsupial have ever been found, all from a small region of southern Peru (2) (3). Anderson’s mouse opossum is a Marmosa, or slender mouse opossum, named for their similarity in appearance to mice. The dark grey fur on the upper parts is relatively long and tipped with reddish-brown, whist the underparts are paler. The hair on the cheeks and chin is cream coloured, and prominent black rings surround the eyes (3). Anderson’s mouse opossum has large thin ears, providing acute hearing (4). The tail, which is longer than the head and body, is furry at the base, with bristles that become longer and more slender towards the tip (3). Each foot has five digits and the big toe on the hindfoot is opposable, which, along with its prehensile (grasping) tail, makes Anderson’s mouse opossums well-adapted for a life in the trees (4)

Opossum-souris D´anderson.
Head-body length: 124 – 125 mm (2)
Tail length: 175 - 193 mm (2)
28 - 38 g (2)

Anderson’s mouse opossum biology

Anderson’s mouse opossum is known only from one individual collected in 1954 (3), and several more specimens caught in the late 1990s (2), and thus very little is known about the biology of this incredibly rare animal. However, much can be deduced from studies of closely related species. It is likely to be nocturnal, and spend most of its time in trees (1). Like all marsupials, gestation is probably short, with females’ giving birth to poorly developed young and most of the development taking place during lactation (4). It is likely that reproduction is similar to that of Marmosa robinsoni, which gives birth to 6 to 14 young after a gestation period of just 14 days. The tiny young, measuring only up to 12 millimetres, attach themselves to the mother’s mammae where they may remain for around 30 days (5). Unlike many marsupials, female mouse opossums do not possess a pouch to protect the young as they develop (4). The young are so un-developed their eyes do not open until 39 to 40 days. It is likely that the young are completely weaned after around 65 days, and they may have an incredibly short life span of only one year (5). Marmosa species build nests for shelter, or use abandoned bird nests, holes in trees, or banana stalks. These nest sites are unlikely to be permanent; rather, the opossum will use whatever site is available as the sun begins to rise (5). Like M. robinsoni, it is likely that Anderson’s mouse opossum is insectivorous, with fruit also playing an important role in the diet (5).


Anderson’s mouse opossum range

Anderson’s mouse opossum is known from only three localities, within a narrow strip along the base of the Andes, in Cusco, southern Peru (1) (2) (3).


Anderson’s mouse opossum habitat

Little is known about the habitat requirements of this species, except that it has been found in lowland tropical rainforest, below 1,000 metres, often around bamboo thickets (2). It is thought that the species is arboreal (1) (3), but specimens were not found more than three metres above the ground (2).


Anderson’s mouse opossum status

Classified as Data Deficient (DD) on the IUCN Red List (1).

IUCN Red List species status – Data Deficient


Anderson’s mouse opossum threats

Anderson’s mouse opossum is particularly vulnerable due to its intrinsically small range, and presumed tiny population. Despite the isolation of the region in which the specimens were found, the habitat still faces a number of threats, including expanding agriculture, overgrazing and unsustainable timber extraction (6). Such threats are likely to impact greatly on this tree-dwelling species.


Anderson’s mouse opossum conservation

There are no known conservation measures currently in place for Anderson’s mouse opossum. It has been proposed that surveys should be undertaken to establish this species’ population size and distribution (7), information that could then be used to implement appropriate conservation measures to protect this unique marsupial.

View information on this species at the UNEP World Conservation Monitoring Centre.

Find out more

For further information on Anderson’s mouse opossum see:



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An animal which lives or spends a large amount of time in trees.
The state of being pregnant; the period from conception to birth.
Feeding on insects.
An organ of female mammals that contains milk-producing glands, a mammary gland.
A diverse group of mammals characterised by their reproduction, in which gestation is very short, and the female typically has a pouch (marsupiam) 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.
Active at night.
Referring to a digit, (thumb or toe), that can be turned so that its pad makes contact with the pad of each of the other digits on the same limb.


  1. IUCN Red List (June, 2009)
  2. Solari, S. and Pine, R.H. (2008) Rediscovery and redescription of Marmosa (Stegomarmosa) andersoni Pine (Mammalia: Didelphimorphia: Didelphidae), an endemic Peruvian mouse opossum, with a reassessment of its affinities. Zootaxa, 1756: 49 - 61.
  3. Pine, R.H. (1972) A new subgenus and species of Murine opossum (Genus Marmosa) from Peru. Journal of Mammalogy, 53: 279 - 282.
  4. Macdonald, D.W. (2006) The Encyclopedia of Mammals. Oxford University Press, Oxford.
  5. O’Connell, M.A. (1983) Marmosa robinsoni. Mammalian Species, 203: 1 - 6.
  6. Alonso, A., Dallmeier, F. and Campbell, P. (2001) Urubamba: The Biodiversity of a Peruvian Rainforest, SI/MAB Series 7. Smithsonian Institution, Washington, DC.
  7. EDGE of Existence (October, 2007)

Image credit

Head of the holotype specimen of the Anderson's mouse opossum  
Head of the holotype specimen of the Anderson's mouse opossum

© Sergio Solari, Field Museum of Natural History

Sergio Solari


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