Cryptonanus chacoensis

Geographic Range

Chacoan mouse opossums (Cryptonanus chacoensis) can be found in central South America. These animals have been reported in northern Argentina, Paraguay, southern Bolivia and Mato Grosso, Brazil. They are also believed to occur in Uruguay, although it is unconfirmed. In total, these animals have been reported in 20 different localities. (Carmignotto, et al., 2011; Gardner, 2008)


Chacoan mouse opossums are usually found in fairly wet seasonally flooded areas of forest, grassland or marshland. Members of their genus have also been found in a variety of human disturbed areas such as eucalyptus plantations, as well as non-forested tropical and subtropical areas. These animals have been captured in hallow logs, wood piles and at the base of fruiting bromeliads. Chacoan mouse opossums have been found from 50 to 1,800 m in elevation. (Carmignotto, et al., 2011; Gardner, 2008; Umetsu and Pardini, 2007; Voss, et al., 2005)

  • Range elevation
    50 to 1,800 m
    164.04 to ft

Physical Description

Genus Cryptonanus is a very recently described group. Until 2005, members of genus Cryptonanus were grouped in genus Gracilinanus. Prior to being given their own unique species name, Chacoan mouse opossums were included in Gracilinanus agilis. As a result, there is currently very little information available specific to Chacoan mouse opossums. (Carmignotto, et al., 2011; Voss, et al., 2005)

Members of genus Cryptonanus share many physical similarities to members of their former genus, Gracilinanus. Some key features that distinguish these animals are the smaller body size, rostrum, orbits, ears and vibrissae of genus Cryptonanus. Chacoan mouse opossums are very small marsupials, weighing between 14 and 16 grams. Their total body length is less than 260 mm; however, that includes a 95 to 117 mm sparsely furred tail. Dorsally, their fur is solid gray to reddish-brown, with short guard hairs. Their ventral pelage is usually soft gray. Members of this genus have a thin, dark facial mask surrounding their eyes, in comparison, the fur of their cheeks and crown is very light. These animals do not have a pouch. (Garcia, et al., 2010; Gardner, 2008; Voss, et al., 2005)

  • Range mass
    14 to 16 g
    0.49 to 0.56 oz
  • Range length
    260 (high) mm
    10.24 (high) in


The mating system of Chacoan mouse opossums has not been reported, however, didelphids generally engage in a polygynous mating system. Male didelphids usually approach receptive females with a series of clicking sounds. These animals generally do not show courtship rituals or long term pair bonds. (Fernandes, et al., 2010; O'Connell, 2006)

There is currently very little information available on the reproductive behavior specific to Chacoan mouse opossums. These animals do not have a pouch. Reportedly, Chacoan mouse opossums may have litters of up to 12 young, however, that report has been challenged, particularly because these animals only have 9 mammae. In general, members of family Didelphidae have seasonal reproduction and a very short gestation period, which typically lasts less than 2 weeks. After birth, their tiny altricial young must climb to their mother’s mammae and attach themselves while their development is completed. Although many of their systems and organs have not yet formed at the time of their birth, didelphids are born with highly developed forelimbs, which facilitates their climb to the mammae. (Astua, 2009; Feldhamer, et al., 2004; Gardner, 2008; O'Connell, 2006; Voss, et al., 2005)

Within Chacoan mouse opossums’ former genus, Gracilinanus; the extreme competition among males for breeding females causes a massive amount of stress. As a result, agile opossums are considered partially semelparous because many of the males die shortly after breeding. This trend is considered only partial because a few males do survive to a second or even third breeding season. However, it is not known whether Chacoan mouse opossums share a similar affliction. (Coopers, et al., 2009; Martins, et al., 2006)

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

The parental investment of Chacoan mouse opossums has not been studied. In general, however, didelphids remain near their mothers and continue weaning for a short time after their attachment to the mammae. At this time, young may even travel on their mother’s back during nighttime excursions. There is no evidence of male parental care. (Nowak, 1999; Wilson, 2000)


There is currently no information available regarding the lifespan of Chacoan mouse opossums. However, agile opossums, the species that Chacoan mouse opossums were grouped in until recently, are very short-lived, typically surviving no more than 1 to 1.5 years. (Coopers, et al., 2009)


Chacoan mouse opossums are nocturnal and primarily use terrestrial locomotion, however, they also create nests up to 1.6 meters above ground. Their nests may be found in tree holes and near bromeliads, these animals use a variety of nesting substrates and have also been discovered in hallow logs and in wood piles. (Gardner, 2008; Umetsu and Pardini, 2007; Voss, et al., 2005)

Home Range

There is currently no information available regarding the home range size of Chacoan mouse opossums.

Communication and Perception

The communication and perception of Chacoan mouse opossums has not been reported. However, in general, members of family Didelphidae have fairly well-developed eyesight and hearing. Their vision is specialized for nocturnal behavior, with light gathering capabilities similar to a cat. Although their visual acuity is generally poor compared to primates, their ability to navigate the forest and capture prey is not hampered. They may use visual displays such as opening their mouth or curling their lips when they perceive danger. Didelphids are not generally noisy animals; however, they may chip, moan, hiss, scream, click and growl. Their sensitivity to tones and general sounds may be fairly under-developed; however, didelphids are very sensitive to high frequency sounds. Olfaction is also an important means of communication for family Didelphidae. Males often scent mark to attract breeding females. Scent may also be used to maintain contact between mothers and their offspring. (Aitkin, 1998; Fadem and Cole, 1985; Frost and Masterton, 1994; Holmes, 1992; O'Connell, 2006; Oswaldo-Cruz, et al., 1979; Volchan, et al., 2004)

Food Habits

The food habits of Chacoan mouse opossums have not been reported. However, their proximity to fruiting bromeliads may suggest it as a food source. In general, members of family Didelphidae are considered opportunistic omnivores, which alter their diet due to seasonally available food items. Agile opossums, the species that Chacoan mouse opossums were recently extirpated from, are considered primarily insectivorous and somewhat frugivorous. (Coopers, et al., 2009; Feldhamer, et al., 2004; Gardner, 2008; Voss, et al., 2005)


The only confirmed predator of genus Cryptonanus are barn owls, unidentified members of the genus have been discovered in the pellets of these owls. Members of genus Gracilinanus are reportedly preyed upon by white-tailed hawks, striped owls, coatis and ocelots. (Bianchi and Mendes, 2007; Ferreira, et al., 2013; Granzinolli and Motta-Junior, 2006; Martinelli, et al., 2011; Motta-Junior, et al., 2004; Souza, et al., 2010)

Ecosystem Roles

Very little is known of the ecosystem roles played by Chacoan mouse opossums. Similar species in genus Gracilinanus are known to be important seed dispersers. Likewise, members of genus Gracilinanus are known to carry nematodes and lice. (Creighton and Gardner, 2008; Torres, et al., 2007; de Camargo, et al., 2011)

Economic Importance for Humans: Positive

There are no known positive economic impacts of Chacoan mouse opossums.

Economic Importance for Humans: Negative

There are no known negative economic impacts of Chacoan mouse opossums, although these animals have been reported residing in eucalyptus plantations. (Umetsu and Pardini, 2007)

  • Negative Impacts
  • crop pest

Conservation Status

Currently, Chacoan mouse opossums are listed as a species of least concern according to the IUCN Red List of Threatened Species. Their relatively large population size, wide distribution and presence in protected areas has helped keep the species stable. (Carmignotto, et al., 2011)

Other Comments

This species has been re-defined into new genera several times. In 1931, this species was included in Marmosa agilis chacoensis, in 1958, this species was included in Marmosa agilis agilis, in 1989, these animals were included in Gracilinanus agilis and in 2005 these animals were placed in a new genus and called Cryptonanus chacoensis. Genus Cryptonanus includes 5 other didelphids. (Voss, et al., 2005)


Leila Siciliano Martina (author), 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


living in landscapes dominated by human agriculture.


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.


marshes are wetland areas often dominated by grasses and reeds.


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.


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


uses touch to communicate


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.


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