Thylamys macrurusParaguayan fat-tailed mouse opossum(Also: long-tailed fat-tailed opossum)

Geographic Range

Thylamys macrurus is distributed in Paraguay east of the Rió Paraguay and across the Brazilian border into the state of Mato Grosso do Sul. (Carmignotto and Monfort, 2006; Giarla, et al., 2010; Voss, et al., 2009)


In Brazil, this species has been captured in the Cerrado, a relatively dry, savanna habitat. In Paraguay, this species has been captured in subtropical moist forest. Little is known about its natural history. (Carmignotto and Monfort, 2006; Giarla, et al., 2010; Voss, et al., 2009)

Physical Description

Thylamys macrurus is larger than other Thylamys species on average, but possesses most of the other external features shared by members of this genus, including an incrassate (fatty) tail. Caceres et al. (2007) found that males are significantly larger than females (52.4 g vs. 41.0 g). Voss et al. (2009) noted a range in mass from 30 g to 57 g, with total body lengths ranging from 251 mm to 308 mm. (Caceres, et al., 2007; Carmignotto and Monfort, 2006; Voss, et al., 2009)

  • Sexual Dimorphism
  • male larger
  • Range mass
    30 to 57 g
    1.06 to 2.01 oz
  • Range length
    251 to 308 mm
    9.88 to 12.13 in


No data exists on the mating system of Thylamys macrurus.

No data exists on the reproductive behavior of Thylamys macrurus.

  • Key Reproductive Features
  • gonochoric/gonochoristic/dioecious (sexes separate)
  • sexual
  • Breeding interval
    Not known.
  • Breeding season
    Not known.

No data exists on the reproductive behavior of Thylamys macrurus.

  • 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


No data exists on the lifespan of Thylamys macrurus.


Little data exists on the behavior of Thylamys macrurus, though it has ben observed and captured on the ground and in trees, suggesting a scansorial locomotory behavior (Caceres et al. 2007). (Caceres, et al., 2007)

Communication and Perception

No data exists on the communication and perception abilities of Thylamys macrurus.

Food Habits

Little is known about the diet of this species. Most Thylamys species primarily consume insects.


No data exists on the predators of Thylamys macrurus.

Ecosystem Roles

Little data exists on the ecosystem roles of Thylamys macrurus. Caceres et al. (2007) identified one tick and one louse species living on Thylamys macrurus individuals. (Caceres, et al., 2007)

Commensal/Parasitic Species

Economic Importance for Humans: Positive

No data exists on the economic value of Thylamys macrurus on humans.

Economic Importance for Humans: Negative

No data exists on the economic value of Thylamys macrurus on humans.

Conservation Status

The IUCN considers Thylamys macrurus Near Threatened as a result of extensive habitat conversion to agriculture and as a result of logging.


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


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.

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.


uses smells or other chemicals to communicate


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.


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.


remains in the same area


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


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.


Caceres, N., R. Napoli, W. Lopes, J. Casella, G. Gazeta. 2007. Natural history of the marsupial Thylamys macrurus (Mammalia, Didelphidae) in fragments of savannah in southwestern Brazil. Journal of Natural History, 41: 1979-1988.

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

Voss, R., P. Myers, F. Catzeflis, A. Carmignotto, J. Barreiro. 2009. The Six Opossums of Felix de Azara: Identification, Taxonomic History, Neotype Designations, and Nomenclatural Recommendations. Bulletin of the American Museum of Natural History, 331: 406-433.