Marmosa isthmica

Geographic Range

Marmosa isthmica occurs in the humid tropical lowlands of Panama, western Colombia, and western Ecuador (Rossi, et al., 2010)


This species occurs in lowland and premontane rainforest, but field studies suggest that it is much more abundant in secondary growth than in primary forest. (Enders, 1935; Rossi, et al., 2010)

  • Range elevation
    0 to 1700 m
    0.00 to 5577.43 ft

Physical Description

Like other species of mouse opossums, Marmosa isthmica is a small, pouchless marsupial with large, membranous ears; prominent eyes; a mask of dark fur surrounding the eyes; and a long, slender, prehensile tail. The dorsal fur is usually reddish brown and the ventral fur is yellowish or orangish. Among other diagnostic traits, this species differs from other species of Marmosa by lacking palatine fenestrae (always present in sympatric M. robinsoni); and by having small, laterally compressed, and ventrally pointed auditory bullae (the bullae are larger, more rounded, and ventrally smooth in M. robinsoni). This species is sexually dimorphic (males are larger than females). (Rossi, et al., 2010)

  • Sexual Dimorphism
  • male larger
  • Range mass
    40 to 143 g
    1.41 to 5.04 oz
  • Average mass
    59 (females), 99 (males) g
  • Range length
    105 to 200 mm
    4.13 to 7.87 in
  • Average length
    140 (females), 161 (males) mm




Breeding is seasonal in this species, but other aspects of the mating system are unknown. (Enders, 1935)

This species is believed to breed once a year, probably in the late dry season (late February and March, in central Panama). The litter size at birth is not known, but the number of offspring attached to the teats of trapped females ranges from 6 to 12. Ovulation is probably spontaneous (as in other species of Marmosa). (Enders, 1935; Rossi, et al., 2010)

  • Breeding interval
    Individuals breed once per year; it is not known whether any breed more than once.
  • Breeding season
    Breeding occurs in the late dry season.
  • Range number of offspring
    6 to 12
  • Average number of offspring

As in other opossums, the young are highly altricial and attach themselves firmly to the mother's nipples for some time after birth. No form of parental care other than female lactation has been recorded. (Enders, 1935)

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


Nothing is known about the longevity of this species in the wild or in captivity.


Like other species of Marmosa, M. isthmica is arboreal/scansorial, nocturnal, nonmigratory, and solitary. Field observations suggest that it prefers to climb on small-diameter substrates (narrow branches and vines). Captive specimens are highly aggressive when competing for food with conspecifics or other small mammals. (Enders, 1935; Park, et al., 1940)

Home Range

Nothing is known about the home range of this species, but local populations appear to fluctuate greatly in abundance from year to year, so spacing is probably highly variable. (Enders, 1935)

Communication and Perception

The eyes, ears, nasal turbinates (thin bones that support olfactory epithelium), and tactile hairs are well developed in this species (as in other opossums), so vision, hearing, and touch are probably important senses. Males have sternal glands that are presumably used for social scent-marking. (Gutierrez, et al., 2010)

Food Habits

Observations of captive animals suggest that this species is largely insectivorous, but it also eats fruit when available. Large insects (grasshoppers and katydids) are stalked, seized, and then killed by repeated bites to the head and thorax. (Enders, 1935)

  • Animal Foods
  • insects
  • Plant Foods
  • fruit


Little is known about the natural predators of this species, but they probably include snakes, owls, and wild felids. ()

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

This species is a primary consumer (of fruits) and a secondary consumer (of insects); it is the prey of owls, and probably also of snakes and carnivorans; and it is the host of both internal and external parasites. Probable ectoparasites include species of Arachnida (Acari: mites) and Insecta (Siphonaptera: fleas). Probable endoparasites include species of Acanthocephala (spiny-headed worms), Cestoda (tapeworms), Digenea (flukes), and Nematoda (roundworms). (Enders, 1935)

Economic Importance for Humans: Positive

It is doubtful that this species has any positive economic impact.

Economic Importance for Humans: Negative

There are no known adverse effects of Marmosa isthmica on humans.

Conservation Status

This species is widely distributed and can live in human-modified landscapes, so it seems to be of no immediate conservation concern. (Enders, 1935; Rossi, et al., 2010)

Other Comments

Between 1951 and 2010 this species was consistently misidentified as Marmosa robinsoni. Phylogenetic analyses of cytochrome-b sequence data, however, suggest that it is most closely related to M. zeledoni and M. mexicana. (Gutierrez, et al., 2010; Rossi, et al., 2010)


Robert Voss (author), American Museum of Natural History, Sharon Jansa (editor), American Museum of Natural History, Alexa Unruh (editor), Animal Diversity Web Staff.



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


An animal that eats mainly insects or spiders.


offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).


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


rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.

scent marks

communicates by producing scents from special gland(s) and placing them on a surface whether others can smell or taste them

seasonal breeding

breeding is confined to a particular season


remains in the same area


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.


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.


Enders, R. 1935. Mammalian life histories from Barro Colorado Island, Panama. Bulletin of the Museum of Comparative Zoology, 78: 383-502.

Gutierrez, E., S. Jansa, R. Voss. 2010. Molecular systematics of mouse opossums (Didelphidae: Marmosa): assessing species limits using mitochondrial DNA sequences, with comments on phylogenetic relationships and biogeography. American Museum Novitates, 3692: 1-22.

Park, O., A. Barden, E. Williams. 1940. Studies in nocturnal ecology, IX. Further analysis of activity of Panama rainforest animals. Ecology, 21: 122-134.

Rossi, R., R. Voss, D. Lunde. 2010. A revision of the didelphid marsupial genus Marmosa. Part 1. The species in Tate's 'mexicana' and 'mitis' sections and other closely related forms. Bulletin of the American Museum of Natural History, 334: 1-81.