Thylamys sponsoriusArgentine fat-tailed mouse opossum

Geographic Range

Thylamys sponsorius is distributed in the eastern foothills of the Andes, extending from southern Bolivia into northern Argentina. (Giarla, et al., 2010)


Thylamys sponsorius primarily inhabits mid-level montane forests and seasonally dry forests between 515 and 3750 meters above sea level in the eastern Andes. This species overlaps in distribution with Thylamys venustus and Thylamys pallidior. (Giarla, et al., 2010)

  • Range elevation
    515 to 3750 m
    1689.63 to 12303.15 ft

Physical Description

Like other members of its genus, Thylamys sponsorius 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 grayish ventral region. This species is very similar in morphology to its sister species Thylamys venustus, though it tends to be slightly larger. Like Thylamys venustus, this species has a relatively long tail that is considerably longer than its body. Giarla et al. (2010) report head + body lengths that range from 86 to 119 mm (average 99 mm) and tail lengths that range from 125 to 154 mm long (average 138 mm). (Giarla, et al., 2010)

  • Range length
    211 to 273 mm
    8.31 to 10.75 in
  • Average length
    237 mm
    9.33 in


Little is known about the mating system in Thylamys sponsorius.

Little is known about the general reproductive behavior of Thylamys sponsorius.

  • Key Reproductive Features
  • gonochoric/gonochoristic/dioecious (sexes separate)
  • sexual
  • viviparous

Little is known about parental investment in Thylamys sponsorius. 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. (Giarla, et al., 2010)

  • Parental Investment
  • altricial
  • female parental care
  • pre-fertilization
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female


No records of this species' lifespan are available.


Little is known about the behavior of Thylamys sponsorius. This species is likely solitary, as most small, insectivorous mammals are. As is the case for other members of this genus, Thylamys sponsorius is nocturnal and experiences daily torpor. Like other members of the genus Thylamys, individuals likely build nests out of grass, hair, feathers, and leaves in rocks, trees, and under shrubs (Braun et al., 2010). Thylamys species are primarily terrestrial but are also skilled at climbing bushes and small trees. (Braun, et al., 2010; Palma, 1997)

Home Range

No data on the home range of this species are available.

Communication and Perception

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. (Palma, 1997)

Food Habits

Little is known about the food habits of this species. Like other Thylamys species, Thylamys sponsorius likely consumes insects and perhaps occasionally eats small vertebrates, leaves, fruit, seeds, and carrion (Palma 1997). (Palma, 1997)


Like other small mammals, Thylamys sponsorius is likely well adapted to avoiding predators by being nocturnal and inconspicuous. No records of known predators are available. (Giarla, et al., 2010)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

Thylamys sponsorius 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 sponsorius is not presently available. (Giarla, et al., 2010; Palma, 1997)

Economic Importance for Humans: Positive

There are no known positive impacts of Thylamys sponsorius on humans.

Economic Importance for Humans: Negative

There are no known negative impacts of Thylamys sponsorius.

Conservation Status

This species is listed by the IUCN as "Least Concern".


Tom Giarla (author), University of Minnesota, Sharon Jansa (editor), American Museum of Natural History, Robert Voss (editor), American Museum of Natural History, Tanya Dewey (editor), University of Michigan-Ann Arbor.



living in the southern part of the New World. In other words, Central and South America.

World Map


uses sound to communicate


young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.


Referring to an animal that lives in trees; tree-climbing.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.


an animal that mainly eats meat


uses smells or other chemicals to communicate


having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.


animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

female parental care

parental care is carried out by females


forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.


An animal that eats mainly insects or spiders.


having the capacity to move from one place to another.


This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.

native range

the area in which the animal is naturally found, the region in which it is endemic.


active during the night


reproduction that includes combining the genetic contribution of two individuals, a male and a female


lives alone


uses touch to communicate


the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.


movements of a hard surface that are produced by animals as signals to others


uses sight to communicate


reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.


Braun, J., N. Pratt, M. Mares. 2010. Thylamys pallidior (Didelphimorphia: Didelphidae). Mammalian Species, 42(856): 90-98.

Giarla, T., R. Voss, S. Jansa. 2010. Species Limits and Phylogenetic Relationships in the Didelphid Marsupial Genus Thylamys Based on Mitochondrial DNA Sequences and Morphology. Bulletin of the American Museum of Natural History, 346: 1-67.

Palma, R. 1997. Thylamys elegans. Mammalian Species, 572: 1-4.