Shrewish short-tailed opossum (Monodelphis sorex)
|Also known as:||Hensel’s short-tailed opossum, red-sided short-tailed opossum, southern red-sided opossum|
|French:||Opossum-musaraigne À Queue Courte|
|Spanish:||Colicorto Musaraña, Colicorto Rojizo|
|Size||Head-body length: 11 - 13 cm (2)|
Tail length: 6.5 - 8.5 cm (2)
|Weight||48 g (2)|
Classified as Least Concern (LC) on the IUCN Red List (1).
A small and rather dull-coloured opossum (2), the shrewish short-tailed opossum is aptly named after its shrew-like appearance, but is in fact a marsupial. Like other short-tailed opossums, the species has small, rounded ears, relatively small eyes, a long, pointed nose, and a tail which is about half as long as the body (3) (4) (5). The head, neck and forequarters of the shrewish short-tailed opossum are grey, with a dark brown back and reddish rump, and the cheeks and the sides of the body are reddish, contrasting with creamy-yellow to pale reddish underparts. The fur is short and smooth, and the tail is only thinly haired. The feet are reddish in colour (2) (3) (4) (6). The shrewish short-tailed opossum shows great sexual dimorphism in size, with the male being up to 50 percent larger than the female (6).
The shrewish short-tailed opossum was originally described on the basis of young specimens, with the adults often being referred to as a separate species, Monodelphis henseli (6). The adult is also often confused with the yellow-sided or southern short-tailed opossum, Monodelphis dimidiata, but can be distinguished by its reddish rather than white or buffy feet, its shorter fur, and reddish rather than tawny yellow sides, and by its preference for forest rather than grassland habitats (2) (6).
The shrewish short-tailed opossum occurs in southeastern Brazil, from Minas Gerais to Rio Grande do Sul, in southern Paraguay to Misiones province, and in northeastern Argentina (2) (3) (4) (7).
The shrewish short-tailed opossum is endemic to humid rainforest within South America’s coastal Atlantic Forest region (1) (2) (6).
Short-tailed opossums live mainly on the ground, being less well adapted for climbing than other opossums (5) (7). Thought to be most active at dusk and dawn (1) (4), the shrewish short-tailed opossum feeds mainly on insects, although it will also take some fruits and small vertebrates (8). Like other opossums, it is likely to be a solitary animal (5).
Although little information is available on the breeding behaviour of this species (6), it is likely that, as in other Monodelphis species, breeding occurs throughout the year (7). As is typical in marsupials, the young are born early and poorly developed, with most development taking place after birth, during a prolonged lactation period (5). Unlike many marsupials, the female shrewish short-tailed opossum does not possess a pouch to protect the young as they develop (2) (5) (6). Instead, the young cling to the mother’s mammae (nipples), and later on may ride on her back and flanks (7). Interestingly, the female shrewish short-tailed opossum has the largest number of mammae of any mammal (up to 27). This, together with the extreme sexual dimorphism and the high number of immature individuals that have been collected, suggests that the species is semelparous, meaning it breeds only once, producing a single, large litter of offspring, and then dies, possibly all within its first year of life (3).
The shrewish short-tailed opossum is in need of more thorough population surveys, but is believed to be undergoing a decline as a result of habitat destruction (1) (6). The Atlantic Forest is one of the world’s most seriously threatened habitats, with less than 10 percent of the original forest area now remaining. Threats to this unique region include plantations, logging and urban expansion, and much of the remaining forest is highly fragmented (6) (9).
The shrewish short-tailed opossum is currently listed as Least Concern on the IUCN Red List, and occurs in a number of protected areas (1), such as Serra dos Órgãos National Park and Serra do Itajaí National Park in Brazil (10) (11). However, it is still a relatively little-known species, and in need of more research. No specific conservation measures are known to be in place for the shrewish short-tailed opossum, and many of the remaining fragments of its Atlantic Forest home are still in need of protection. However, despite the many threats facing this habitat, a range of conservation efforts are now underway in the region (9), and, if successful, these could help secure a brighter future for this diminutive marsupial.
To find out more about the Atlantic Forest and its conservation, see:
Biodiversity Hotspots - Atlantic Forest:
To read more about short-tailed opossums and other South American mammal species, see:
Gardner, A.L. (2008) Mammals of South America. Volume 1: Marsupials, Xenarthrans, Shrews, and Bats. University of Chicago Press, Chicago.
Emmons, L.H. (1997) Neotropical Rainforest Mammals: A Field Guide. Second Edition. University of Chicago Press, Chicago.
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- Atlantic Forest: a highly biodiverse region found along the east coast of South America, comprising several different vegetation types, including high-altitude grassland, and lowland and montane forest. The coastal Atlantic forest is a narrow strip of about 50 to 100 kilometres along the coast, which covers about 20 percent of the Atlantic Forest region.
- Endemic: a species or taxonomic group that is only found in one particular country or geographic area.
- Mammae: the organs of females that contain milk-producing glands.
- Marsupial: 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.
- Sexual dimorphism: when males and females of the same species differ in appearance.
- Vertebrate: animal with a backbone.
IUCN Red List (December, 2009)