Thylamys karimiiKarimi's fat-tailed mouse opossum

Geographic Range

Thylamys karimii occurs south of the Amazonian rainforest in the Brazilian states of Bahia, Goiás, Mato Grosso, Minas Gerais, Pernambuco, Piauí, Rondônia, and Tocantins (Carmignotto and Monfort 2006). (Carmignotto and Monfort, 2006)


Thylamys karimii has been collected in both the Cerrado (tropical savanna) and Caatinga (semi-arid shrubland) ecoregions of Brazil. Like most other Thylamys species, T. karimii appears to prefer open-canopy habitats instead of closed canopy forests. (Carmignotto and Monfort, 2006; Giarla, et al., 2010)

  • Range elevation
    342 to 1171 m
    1122.05 to 3841.86 ft

Physical Description

Like other members of its genus, Thylamys karimii 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 (though some individuals might not obviously display this pattern; Carmignotto and Monfort, 2006). This species can be distinguished from its closest relative, Thylamys velutinus, by fully white hairs on its ventral region (as opposed to gray-based hairs in T. velutinus). Carmignotto and Monfort (2006) report head + body lengths that range from 78 to 129 mm (average 104 mm), tail lengths that range from 69 to 106 mm long (average 80 mm), and body weights that range from 16 to 43 g (average 28 g). Carmignotto and Monfort (2006) also observed weak sexual dimorphism in several cranio-dental characters and pelage characters, but only among adults. (Carmignotto and Monfort, 2006; Giarla, et al., 2010)

  • Sexual Dimorphism
  • sexes colored or patterned differently
  • sexes shaped differently
  • Range mass
    16 to 43 g
    0.56 to 1.52 oz
  • Average mass
    28 g
    0.99 oz
  • Range length
    147 to 235 mm
    5.79 to 9.25 in
  • Average length
    184 mm
    7.24 in


Carmignotto and Monfort (2006) captured juvenile Thylamys karmii individuals in both the wet and dry season, which suggests that this species might breed year-round. However, little is known about any other aspect of this species' reproduction. (Carmignotto and Monfort, 2006)

Little is known about the reproductive behavior of Thylamys karimii.

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

Little is known about parental investment in Thylamys karimii. 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
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female


The lifespan of this species is not known.


Little is known about the behavior of Thylamys karimii. This species is likely solitary, as most small, insectivorous mammals are. As is the case for other members of this genus, Thylamys karimii is nocturnal and probably enters torpor during the day. (Giarla, et al., 2010)

Home Range

The home range of this species has not been studied.

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 karimii likely consumes insects and perhaps occasionally eats small vertebrates, leaves, fruit, seeds, and carrion (Palma 1997). (Palma, 1997)

  • Animal Foods
  • carrion
  • insects
  • terrestrial non-insect arthropods
  • Plant Foods
  • leaves
  • seeds, grains, and nuts
  • fruit


Like other small mammals, Thylamys karimii 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 karimii 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 karimii is not presently available. (Carmignotto and Monfort, 2006; Giarla, et al., 2010; Palma, 1997)

Economic Importance for Humans: Positive

There are no known positive impacts of Thylamys karimii.

Economic Importance for Humans: Negative

There are no known negative effects of Thylamys karimii.

Conservation Status

Thylamys karimii is listed as "Vulnerable" according to the IUCN Red List due to habitat destruction in the Brazilian Cerrado and Caatinga.


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


flesh of dead animals.


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


An animal that eats mainly insects or spiders.


having the capacity to move from one place to another.

native range

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


active during the night

scrub forest

scrub forests develop in areas that experience dry seasons.


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


lives alone


uses touch to communicate


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.


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.


Carmignotto, A., T. Monfort. 2006. Taxonomy and distribution of the Brazilian species of Thylamys (Didelphimorphia: Didelphidae). Mammalia, 70: 126–144.

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.