Aceramarca Gracile Mouse Opossum
(Gracilinanus aceramarcae)
A delicately built mouse opossum, with a slender tail and a dark brown eye-ring. Unlike the more familiar Australian marsupials this opossum does not possess a pouch. Little is known about this cryptic species, as only six specimens have ever been collected. Like other mouse opossums, it is likely to be arboreal and eat fruit and invertebrates. It is classified as Critically Endangered by the World Conservation Union (IUCN) since it is only known from two restricted areas of declining habitat.
Urgent Conservation Actions
Status surveys to establish population size and distribution.
Peru and western Bolivia.
In the past there was a popular misconception that opossums copulated through the nose and that the young were later blown out through the nostrils into the pouch! This idea may have originated from the fact that males have a forked penis, and females have a tendency to lick the pouch area before birth.
Evolutionary Distinctiveness
Order: Didelphimorphia
Family: Didelphidae
Didelphid (American opossum) remains are known from North American fossil deposits dating back 70-80 million years ago. These small marsupials are thought to have entered South America and Europe from North America, but by 10-20 million years ago they had become extinct in both of these regions. Some species re-entered North America when the Isthmus of Panama reformed, connecting North and South America, around 3 million years ago. The family Didelphidae includes 87 species in 17 genera. The genus Gracilinanus (gracile mouse opossums) contains nine species, widely distributed in South America.
Head and body length: approx. 70-135 mm
Tail length: approx. 90-155 mm
Weight: approx. 23-34 g
The gracile mouse opossum is a small, delicately built opossum with no pouch. Fur colouration is generally reddish-brown or greyish-brown above and cream below. The fur on the back is uniformly coloured and unpatterned. There is a dark brown or blackish eye-ring. The tail is slender and usually covered in scales.
It is likely that this species is arboreal, although it may forage for fruit, insects and other small invertebrates on the forest floor.
The species has been found at altitudes of 2,600-3,300 m in tropical cloud forests on the eastern slopes of the Andes Mountains.
The species is known from five specimens from three areas along the eastern slope of the Andes mountains in La Paz Department, Bolivia, and one specimen from Peru.
Population Estimate
Population Trend
Classified as Critically Endangered (CR B1+2c) on the 2006 IUCN Red List of Threatened Species.
The species is known from only from a few restricted areas of declining habitat. Habitat destruction resulting from widespread clearing of brush in the Andes is the main threat.
Conservation Underway
There do not appear to be any conservation measures in place for this species.
Conservation Proposed
Further research into distribution and ecology of this little-known species.
MacDonald, D. (ed.). 2002. The New Encyclopedia of Mammals. Oxford University Press. Oxford.

New World Marsupial Specialist Group 1996. Gracilinanus aceramarcae. In: IUCN 2006. 2006 IUCN Red List of Threatened Species. Downloaded on 19 July 2006.

Nowak, R. M. 1999. Walker’s Mammals of the World. Sixth edition. The Johns Hopkins University Press, Baltimore and London.

Distribution map based on data provided by the IUCN Global Mammal Assessment.

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