This lowland species is distributed in south-eastern Bolivia, western Paraguay, and north-eastern and central Argentina.
Biogeographic Regions: neotropical (Native )
Like other members of its genus, Thylamys pusillus is notable for its incrassate (fattened) tail. The size of the tail varies by season in accordance with food availability. Although this species is a marsupial, females do not have a pouch. This species is tricolored, with darker dorsal fur, paler lateral fur, and a white ventral region. This species is broadly similar morphologically to Thylamys macrurus but much smaller. It is also quite similar to Thylamys pallidior, a species that occurs in some of the same areas as Thylamys pusillus. Dorsal hair length and ventral hair color are useful characters for differentiating between these two species (Giarla et al., 2010). Giarla et al. (2010) report head and body lengths that range from 88 to 116 mm (average 98 mm) and tail lengths that range from 98 to 134 mm long (average 109 mm).
Range length: 186 to 250 mm.
Average length: 207 mm.
Other Physical Features: endothermic ; bilateral symmetry
Thylamys pusillus inhabits the arid and semi-arid lowlands of central South America, including the Chaco, Monte, and Pampas ecoregions.
Range elevation: 0 to 1000 m.
Habitat Regions: tropical
Terrestrial Biomes: desert or dune ; savanna or grassland
Habitat and Ecology
Little is known about the food habits of this species. Like other Thylamys species, Thylamys pusillus likely consumes insects and perhaps occasionally eats small vertebrates, leaves, fruit, seeds, and carrion (Palma 1997).
Primary Diet: carnivore (Insectivore )
Thylamys pusillus likely acts as an important predator to many arthropod species and perhaps some small vertebrates. It is likely prey to both bird and medium-sized mammals, such as owls and foxes. It is also likely host to many ecto- and endoparasites. More specific information about the ecosystem role of Thylamys pusillus is not presently available.
Like other small mammals, Thylamys pusillus is likely well adapted to avoiding predators by being nocturnal and inconspicuous. No records of known predators are available.
Anti-predator Adaptations: cryptic
Life History and Behavior
Because this species is small and nocturnal, communication between individuals is likely primarily olfactory in nature. Palma (1997) reports that the olfactory and visual regions of another Thylamys species' brain are especially well developed.
Communication Channels: visual ; tactile ; acoustic ; chemical
Perception Channels: visual ; tactile ; acoustic ; vibrations ; chemical
No records of this species' lifespan are available.
No published studies have examined mating systems in Thylamys pusillus.
Little is known about the general reproductive behavior of Thylamys pusillus.
Key Reproductive Features: gonochoric/gonochoristic/dioecious (sexes separate); sexual ; viviparous
Little is known about parental investment in Thylamys pusillus. Like all marsupials, females nurse their highly altricial young. However, because members of the genus Thylamys lack a pouch (marsupium), the young must cling to their mother's venter.
Parental Investment: altricial ; female parental care ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Female)
Molecular Biology and Genetics
Statistics of barcoding coverage: Thylamys pusillus
Public Records: 0
Specimens with Barcodes: 1
Species With Barcodes: 1
This species is listed as "Least Concern" by the IUCN.
IUCN Red List of Threatened Species: least concern
IUCN Red List Assessment
Red List Category
Red List Criteria
Relevance to Humans and Ecosystems
There are no known negative effects of Thylamys pusillus.
There are no known positive impacts of Thylamys pusillus on humans.
Common fat-tailed mouse opossum
The Common Fat-tailed Mouse Opossum (Thylamys pusillus) is a species of opossum in the family Didelphidae. It occurs in Argentina, Bolivia, Brazil, and Paraguay in chaco and Andean foothill habitats. Its head-and-body length is about 75 to 120 (mean 94.3) mm, and its tail length is about 90 to 134 (mean 103.6) mm. Its dorsal fur is brownish gray, and its ventral fur is yellowish to white. The legs and cheeks are the same color as the ventral surface. Its tail is sharply bicolored (divided into two colors). A ring of faintly darker fur surrounds each eye. Its tail often lacks fat deposits, but does not always.
- Gardner, A. L. (2005). "Order Didelphimorphia". In Wilson, D. E.; Reeder, D. M. Mammal Species of the World (3rd ed.). Johns Hopkins University Press. p. 18. ISBN 978-0-8018-8221-0. OCLC 62265494.
- Flores, D., de la Sancha, N. & Albanese, M. S. (2011). "Thylamys pusillus". IUCN Red List of Threatened Species. Version 2011.2. International Union for Conservation of Nature. Retrieved 18 January 2012. Database entry includes justification for why this species is of least concern
- Eisenberg, John Frederick; Redford, Kent Hubbard (1999). Mammals of the Neotropics: The Central Neotropics: Ecuador, Peru, Bolivia, Brazil. University of Chicago Press. p. 624. ISBN 978-0-226-19542-1.
- Gardner, Alfred L. (2008). Mammals of South America: Marsupials, xenarthrans, shrews, and bats. University of Chicago Press. p. 669. ISBN 0-226-28240-6.
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