Thylamys pallidiorpallid fat-tailed opossum

Geographic Range

Thylamys pallidior is distributed from southern Peru to central Argentina, including Chile and western Bolivia. (Giarla, et al., 2010)


This species inhabits a number of different dryland habitats, including the high Andean steppe (Puna grassland), the Monte desert and dry Chaco of Argentina, and the Sechura Desert of Peru. For much of its range, it is found in high-elevation habitats of the Andes. At the southern extreme of its distribution, it can be found in lowland areas. (Braun, et al., 2010; Giarla, et al., 2010)

  • Range elevation
    0 to 3750 m
    0.00 to 12303.15 ft

Physical Description

Like other members of its genus, Thylamys pallidior 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 to other members of the Elegans Group (which includes T. elegans, T. pallidior, and T. tatei) as described by Giarla et al. (2010). Giarla et al. (2010) report head + body lengths that range from 73 to 104 mm (average 95 mm) and tail lengths that range from 97 to 118 mm long (average 109 mm). Braun et al. (2010) report body masses ranging from 13 to 39 g (average 19 g) (Braun, et al., 2010; Giarla, et al., 2010)

  • Range mass
    13 to 39 g
    0.46 to 1.37 oz
  • Average mass
    19 g
    0.67 oz
  • Range length
    170 to 222 mm
    6.69 to 8.74 in
  • Average length
    204 mm
    8.03 in


Little is known about the mating system in Thylamys pallidior. Palma (1997) reports that two Thylamys elegans adults (a closely related species) have never been found in the same nest, suggesting that this species does not form monogamous breeding pairs. (Palma, 1997)

Little is known about the general reproductive behavior of Thylamys pallidior. Anecdotal evidence from the early 20th century (reviewed in Braun et al., 2010) suggests that this species and other small opossums breed one to three times per year. Juvenile animals tend to be captured early in the calendar year, with only adult specimens being captured in the last few months of the year. (Braun, et al., 2010)

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

Little is known about the parental care of Thylamys pallidior. Like other Thylamys species, females lack a pouch, with exposed young clinging to the nipples. (Giarla, et al., 2010)

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


Braun et al. (2010) note an account of Thylamys pallidior from the early 20th century wherein a captured juvenile survived for 1.5 years in captivity, tripling in size over its life span. (Braun, et al., 2010)

  • Range lifespan
    Status: captivity
    1.5 (high) years


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

Home Range

No studies have examined the home range of Thylamys pallidior.

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 the brain of Thylamys elegans, a closely related species, are especially well developed. (Palma, 1997)

Food Habits

Albanese et al. (2010) examined the feces of wild Thylamys pallidior individuals and found that its diet primarily consisted of arthropods. Other dietary components include leaves, fruit, and seeds. Other Thylamys species have been observed consuming small vertebrates (e.g. rodents, lizards), so it is possible that Thylamys pallidior also feeds on those prey items (Palma, 1997) (Albanese, et al., 2011; Giarla, et al., 2010; Palma, 1997)

  • Animal Foods
  • insects
  • Plant Foods
  • leaves
  • seeds, grains, and nuts
  • fruit


Like other small mammals, Thylamys pallidior is likely well adapted to avoiding predators by being nocturnal and inconspicuous. This species has been noted as a prey item for two owl species. (Braun, et al., 2010)

  • Anti-predator Adaptations
  • cryptic
  • Known Predators
    • Magellanic horned owls (Bubo magellanicus)
    • common barn owls (Tyto alba)

Ecosystem Roles

Thylamys pallidior acts as an important predator to many arthropod species and some small vertebrates. It is prey to several bird and medium-sized mammals, such as owls and foxes. Braun et al. (2010) list six ecto- and endoparasites associated with Thylamys pallidior. (Braun, et al., 2010)

Commensal/Parasitic Species

Economic Importance for Humans: Positive

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

Economic Importance for Humans: Negative

There are no known negative effects of Thylamys pallidior.

Conservation Status

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


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


Found in coastal areas between 30 and 40 degrees latitude, in areas with a Mediterranean climate. Vegetation is dominated by stands of dense, spiny shrubs with tough (hard or waxy) evergreen leaves. May be maintained by periodic fire. In South America it includes the scrub ecotone between forest and paramo.


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.

desert or dunes

in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots.


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


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


that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).


Living on the ground.


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

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.


A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.


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.


Albanese, S., M. Dacar, R. Ojeda. 2011. Unvarying diet of a Neotropical desert marsupial inhabiting a variable environment: the case of Thylamys pallidior. Acta Theriologica: 1-4. Accessed (Date Unknown) at

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.