Didelphimorphia

New World opossums

(Didelphidae)

Class Mammalia

Order Didelphimorphia

Family Didelphidae

Number of families 1

Thumbnail description
Small- to medium-sized terrestrial mammal with long, naked tail, opposable thumbs both in the hands and feet, long, pointed snout, naked ears that range from small to large, and medium to large eyes; color varies from nearly pure white to blackish; some species are unicolored, whereas others have distinct light and dark blotches and bands

Size
3–22 in (8–55 cm); 0.9 oz–11 lb (25–5,000 g)

Number of genera, species
15 genera; 61 species

Habitat
Dry and moist tropical forests, temperate forest, woodland, grasslands, scrub, and mangroves

Conservation status
Critically Endangered: 3 species; Endangered: 3 species; Vulnerable: 15 species; Near Threatened: 18 species; Data Deficient: 2 species

Distribution
North America from southern Canada and New England to southern Mexico, Central America, and South America to southern Argentina and Chile

Evolution and systematics

This group of mammals was traditionally included in the marsupials until 1993 when it was placed in its own order, Didelphimorphia, together with two other New World opossum-like families, the Microbiotheriidae (one species) and the Caenolestidae (five species). Here Didelphidae is treated in its own order, Didelphimorphia, and Microbiotheriidae and Caenoletidae are each covered in an order as well. The fossil record suggests that didelphids are relatively primitive, unspecialized mammals that emerged some 75–100 million years ago (mya) in North America. Their evolutionary and biogeographical history is complex; they colonized Europe, Asia, and Africa some 60 mya, but disappeared from those continents some 20 million years later, presumably due to competition and predation with the appearance of placental mammals. Twenty mya they were restricted to South America, where they underwent an impressive radiation in the absence of other ecologically similar or predatory placental mammals. It was not until the Isthmus of Panama rose and North and South America joined, some three million years ago at the beginning of the Pleistocene, that the didelphids again entered North America. Throughout this time they retained a remarkably stable morphology. The connection between North and South America also allowed the entrance of other placental mammals into South America. For the first time in 20 million years, marsupials again faced the faster, larger-brained placental competitors and predators. Groups like the Borhyaenids (wolf- or hyena-like marsupials) and Thylacosmilids (marsupial saber-toothed cats) disappeared and gave way to true canids and felids. Some factors that may have contributed to their disappearance are the smaller encephalization quotient, lower metabolic rate and overall speed, and lower cursorial abilities of the marsupials compared to their placental counterparts. Didelphids have relatively low evolutionary rates and a strong stabilizing selection that prevents greater morphological diversification in the group.

The family Didelphidae is arranged into two subfamilies, Caluromyinae and Didelphinae. As of 2002, 15 genera are recognized: woolly opossums (Caluromys), black-shouldered

opossums (Caluromysiops), water opossums (Chironectes), common opossums (Didelphis), bushy-tailed opossums (Glironia), gracile opossums (Gracilinanus), Patagonian opossums (Lestodelphys), lutrine opossums (Lutreolina), mouse opossums (Marmosa), slender mouse opossums (Marmosops), brown four-eyed opossums (Metachirus), woolly mouse opossums (Micoureus), short-tailed opossums (Monodelphis), gray four-eyed opossums (Philander), and fat-tailed mouse opossums (Thylamys). In 1993, Gardner recognized a total of 61 species, but there have been at least three additional species described since then.

Physical characteristics

New World opossums are small- to medium-sized mammals. The tail can be almost completely covered with hair or almost naked, depending on the species, and frequently is bicolored with the distant half whitish and the base dark. When the tail is naked, it is covered with scales. Tail length is as long as or longer than the head and body in all genera except Monodelphis, in which it is about 50% of the head and body length. In most genera, the tail is at least partially prehensile. Ears are always medium to large, rounded and naked, except in the genera Lutreolina and Lestodelphys, in which ears are short. The snout is long and pointed, and eyes are large, sometimes bulging, and black or brown. The mouth is large and can open to a remarkably wide gape. Tooth and skull morphology is notably consistent, indicating the relatively low level of specialization in this group. The dental formula is I5/4 C1/1 PM3/3 M4/4 × 2 = 50. The thumbs are opposable in the hind feet, giving extremities their characteristic grasping ability, although the water opossum has webbed feet to aid in swimming action and its thumbs are only slightly opposable. Arms and legs vary with the genus. Some genera, like Metachirus, have relatively long legs, whereas others like Monodelphis and Lestodelphys have relatively short legs. Except for a few species such as Monodelphis dimidiata, there is no sexual dimorphism.

Coloration varies widely. Some species are uniformly blackish, while others are almost completely whitish; other species are rusty reddish, gray, brown, tan, or yellowish brown. Underparts are nearly always paler than the dorsum. The venter of the water opossum is silvery white. Two genera have distinct dark blotches above the eyes; they are called four-eyed opossums. Some genera have characteristic dark and pale patterns, sometimes broad, dark saddle-like bands across the back, sometimes a longitudinal stripe along the dorsal spine and continuing along the top of the snout and to the tip of the nose. The hair can be short or long depending on the species, but it is always dense. In females of some genera, there is a distinct ventral pouch where young are kept in the developmental stages. The pouch opens circularly and can be almost completely closed. Mammae number 12 to 18 and are arranged in a circle with one in the center. One species, the water opossum, has a pouch that seals hermetically with an oily substance so that females can dive under the water surface without drowning the young that are attached to the nipples. Likewise, males of this species have a pouch, which protects the scrotum and testicles from contact with the water.

Distribution

Individuals belonging to this family inhabit only the New World, from Patagonian Argentina and Chile north to

southern Canada and the northeastern United States. They are much more diverse in the tropical and subtropical regions between Mexico and Argentina, while only a single species, the Virginia opossum (Didelphis virginiana), extends into the United States and Canada. Because of their long period of evolutionary isolation in South America, many genera and species can only be found in that subcontinent. The genera Thylamys, Lestodelphys, one species of Didelphis (D. aurita), three of the six species of Gracilinanus (G. aceramarcae, G. agilis, and G. microtarsus), two species of Marmosops (M. dorothea and M. incanus), one of Micoureus (M. constantiae), and 10 species of Monodelphis (M. americana, M. dimidiata, M. domestica, M. iheringi, M. kunsi, M. osgoodi, M. rubida, M. scallops, M. sorex, and M. unistriata) are restricted to South America south of the Amazon river. Several species of Marmosa, Marmosops, and Thylamys are known only from the type localities, and several genera such as Caluromysiops and Glironia and species such as Gracilinanus emiliae, Marmosa rubra, and Monodelphis americana are restricted to the Amazon basin.

The Virginia opossum is one of the most widespread species in the family, and the only one with a distribution extending well beyond that of any other species. Virtually all other species coexist with one or more additional species of didelphids, but in all of the United States and southern Canada, the Virginia opossum is the only species present. Most species inhabit tropical habitats, but a few species, remarkably in the genera Thylamys and Lestodelphys, are adapted to temperate ecosystems, and inhabit only the southern latitudes of Chile and Argentina.

Habitat

The family Didelphidae can be found in a wide variety of habitats, from moist and dry tropical forests to cloud forests, mangrove swamps, grasslands, scrub, and even into temperate forests. One species, the lutrine opossum or thick-tailed opossum (Lutreolina crassicaudata) is considered to be strongly adapted to life in the South American grasslands or pampas, and readily enters lakes and streams where it swims remarkably well. Another species, the water opossum (Chironectes minimus), has as a primary habitat of streams and lakes in moist forests, making its dens in the banks.

Many species are able tree climbers and also move around on the ground; some individuals have been found high in tropical moist forest canopy trees. Other species are predominantly terrestrial, such as the members of the genera Monodelphis and Metachirus, and appear clumsy if placed in trees, even low to the ground.

Because of their long period of evolutionary isolation in South America, opossums were able to invade virtually every habitat available at every latitude and from sea level to almost 13,100 ft (4,000 m) above sea level. Most species, however, have a relatively restricted habitat and geographic range. Only species such as Didelphis virginiana and D. marsupialis can be found in several varying habitats, from temperate forests to tropical moist and dry forests to mangrove swamps.

Some species are able to exist in human-modified habitats and a few may even benefit from these, by invading banana, coffee, and citrus plantations, corn fields, and other agroecosystems. Other species seem particularly adept at using forest edges and secondary vegetation. Finally, many other species depend on undisturbed habitats and do not tolerate disturbance or deforestation.

Behavior

Nearly all species in the family are nocturnal, although occasionally diurnal sightings of mouse opossums and water opossums have been reported, and some species of Monodelphis are reportedly primarily diurnal. Many scansorial species take to the trees when threatened, whereas terrestrial species run with a characteristic gait. No species is particularly fast during escape behavior. One species, the Virginia opossum, feigns death when threatened by a predator, lying on its side, gaping its mouth spasmodically, and emitting a strong musky smell. Other defense behaviors found in the family include gaping and snapping at intruders while hissing loudly and secreting musk from

the anal region. The water opossum dives under the surface and then propels itself with strong strokes from the hind legs.

All opossums are primarily solitary, avoiding contact with each other. After dispersal, juveniles do not keep contact. Males and females come in contact only during the female estrus for a short period of time. Individuals generally remain in a home range, but this is almost never defended. Instead, when two animals coincide in space and time, they avoid each other. At least in the bare-tailed woolly opossum, Caluromys philander, social dominance is clearly established on the basis of age and body mass. Older, heavier males dominate younger, lighter ones, and agonistic behavior is exacerbated by the presence of females. Interspecific aggression may occur only as a result of the generalized opportunistic behavior to procure food; one Didelphis reportedly attacked, killed, and partially consumed a Philander opossum after an encounter.

Opossums are silent animals the vast majority of the time; sounds are produced only when they are threatened and these are only hisses and explosive gasps. Foraging behavior is exploratory and continuous. Opossums use primarily their sense of smell to locate food. Stalking is seldom used to capture animal prey, but sight and hearing are continually used in the search for food. Young opossums, particularly mouse opossums, emit a loud chirping cry when detached from the female's nipple. This induces the female to approach and grasp the young, and push it under the venter, where it reattaches itself to the nipple.

Predators of opossums include a variety of snakes, foxes, owls, ocelot (Leopardis pardalis), puma (Puma cencolor), and jaguar (Panthera onca). Indigenous human groups in the Neotropical region often include the larger species of opossums in their diet. Didelphis albiventris has been shown to have an antibothropic biochemical factor in its blood and milk that neutralizes the venom of poisonous snakes.

Longevity records in the wild rarely reach two years, with many species barely surpassing one year. In captivity, longevity is extended with reports of three to five years for species such as Marmosa robinsoni, Caluromys philander, and Chironectes minimus. The record is seven years for a captive Caluromysiops irrupta.

Feeding ecology and diet

New World opossums are generalist omnivores. Food items include insects, insect larvae, worms and other invertebrates, bird's eggs and nestlings, fruit, carrion, reptiles, amphibians, birds, and small mammals. Almost all species are omnivorous with varying degrees of frugivorous or carnivorous tendencies. Species in the genera Caluromys and Caluromysiops are considered primarily frugivorous, although they do include animal matter in their diet. Smaller species such as those in the genera Marmosa, Marmosops, Gracilinanus, etc., tend to be primarily insectivorous with some eggs, fruit, and meat also included. Mouse opossums kept in captivity will not hesitate to attack large moths or grasshoppers, grasping them with their hands and quickly administering killing bites all over the body of the insect. They normally discard the wings and legs, and other chitinous, undigestible pieces. Caterpillars are rapidly rolled and rubbed against substrates to remove stinging hairs. Fruit can be plucked off tree branches directly or can be eaten after the fruit has fallen to the ground. Sweet, juicy fruits are preferred, such as zapotes, blackberries, guavas, chirimoyas, etc., although other drier fruits such as wild figs and wild cacao, as well as introduced, human-grown varieties like bananas, figs, citrus fruits, apples, and cherries, are also consumed. Common and four-eyed opossums take large amounts of fruit from secondary forest species such as Cecropia. Common opossums (Didelphis) seem to be better seed dispersers and to invest more in seeking fruits of Cecropia than gray four-eyed opossums (Philander).

The water opossum (Chironectes minimus) is particularly interesting in that it seems to be the only New World opossum species that is completely carnivorous. This species feeds mainly on fish, crustaceans, mollusks, and frogs. Its long fingers and bulbous fingertips are held outstretched while the animal swims. Under water, their hands are used to feel under rocks and logs for potential prey. They coexist and overlap locally with the common Neotropical otter (Lontra longicaudis). In the Old World, in Africa and Asia, common otters coexist with clawless or small-clawed otters (genera Aonyx and Amblonyx), which have similar habits and hand morphology to the water opossum. This allows them to coexist by partitioning food resources. The water opossum and the otter may be in the same situation, with the otter feeding primarily on fish and less on crustaceans and mollusks, whereas the opossum probably takes more invertebrates than fish.

In Mediterranean habitats of South America, Thylamys elegans has been shown to regulate the frequency of torpor periods, and therefore energy expenditure, by the availability of food. When food is plentiful, animals never enter torpor, and frequency of torpor periods increases with decreasing food availability.

Reproductive biology

Information on reproduction is available for only a few species. Some species show one defined reproductive event during the year that coincides with the greatest seasonal abundance of food. Other species, particularly those inhabiting

more tropical climates, may have two reproductive periods every year or even have an indistinct pattern in which reproductive females can be found in every month of the year.

New World opossums are polygamous. Like other marsupials, have a very short gestation period, followed by a long developmental period. After a gestation between 12 and 15 days, the embryo-like newborn, naked, with eyes and ears closed but strong arms and well-developed claws, crawls along a path between the cloaca and the marsupium (or mammary region in those species with no marsupium) that has been licked by the female. Once in the mammary region, each individual attaches to a nipple, where it will remain for four to eight weeks, depending on the species. Offspring can then detach from the nipples for the first time. When they are too large to fit in the female's pouch, they crawl on her back or are simply dragged behind her, while still attached to the mammae. Young remain dependent on their mothers until they are two to four months old, after which they are weaned and proceed to disperse.

Litter size varies greatly in different genera. Five to 12 and up to 16 offspring are born in Monodelphis, two to five in Caluromys, four to 12 in Marmosa, two to five in Chironectes, six to 15 in Didelphis, and one to nine in Philander. Likely, many more young are born than those found by scientists attached to the mammae, but they die before they can attach themselves to a nipple.

Sexual maturity is attained at three to nine months in different genera. Many species construct nests inside rotten trees both standing and fallen, while others have nests on the ground or, in the case of the water opossum, in tunnels excavated in stream banks. Some species of mouse opossum utilize hummingbird nests as their own resting places. New World opossums use primarily plant matter to construct the spherical nests. These materials are transported in the partially rolled-up tail while the animal moves to the nest.

Many species are semelparous with males dying shortly after mating and females after weaning their first and only litter

produced. Females of some species, however, can breed twice in the same year with only a few months apart between births, and individuals of a few species can have two years of reproductive activity.

Conservation status

Of the species recognized by Gardner in 1993, three (Gracilinanus aceramarcae, Marmosa andersoni, and Marmosops handleyi) are considered Critically Endangered by the IUCN, and three other species (Marmosa xerophila, Marmosops cracens, and Monodelphis kunsi) are considered Endangered. All three Critically Endangered species have extremely restricted distributions, limited to one or two localities in Bolivia or Colombia. Although none of these species face direct threats from humans, all are facing rampant habitat destruction that has strong negative conservation implications. The three Endangered species face the same threats of habitat destruction and restricted distributions in Colombia, Venezuela, Bolivia, and Brazil, albeit slightly larger than the Critically Endangered species. Fifteen additional species are considered Vulnerable, 18 more are under the category of Lower Risk/Least Concern, and two are Data Deficient. There are 20 species that have not been ranked by the IUCN. Undoubtedly other species are facing conservation threats, especially those with restricted distributions and found in habitats affected by high rates of deforestation, but much more information is necessary to correctly assess their status.

In Mexico, two species, the water opossum and the woolly opossum, are included in the list of species at risk as endangered. These two species are considered sensitive to habitat disruption and their populations have been severely decreased as a result of deforestation and water pollution by discharge of fertilizers and pesticides.

Significance to humans

Species such as the common opossums and even some four-eyed and mouse opossums frequently benefit from human-induced habitat changes. Some humans find opossum species attractive as pets, and their tanned pelts used to have some value in the fur market, especially at the end of the nineteenth century. In the tropics, mouse opossums and short-tailed opossums are valued for controlling of cockroaches, scorpions, and other unwanted animals, especially in rural settlements. Virginia, common, and four-eyed opossums are sometimes used as food by indigenous and other human populations. Colonies of some species, notably Monodelphis, are kept for developmental and biomedical research.

Opossums are sometimes considered pests because of their raids on commercially valuable fruits in orchards and agricultural fields, as well as on poultry farms. The southern opossum, Didelphis marsupialis, has been identified as one of the key hosts of the parasitic protozoan Trypanosoma cruzi, which causes Chagas' disease. Chagas' disease is transmitted to humans when an infected kissing, or assassin, bug (Hemiptera: Reduviidae; genus Triatoma) bites a human to feed on the blood and then defecates on the skin. The person then scratches the bite and transports the protozoans through an open wound into the body. Sixteen to 18 million people are infected, and 50,000 of these die annually. Other species of mammals have also been identified as hosts.

Species Accounts

List of Species

Bare-tailed woolly opossum

Caluromys philander

subfamily

Caluromyinae

taxonomy

Didelphis philander (Linnaeus, 1758), America, restricted to Surinam; Ghana.

other common names

French: Opossum laineux; German: Gelbe Wollbeutelratte; Spanish: Tlacuache lanudo, comadreja lanuda, cuica lanuda.

physical characteristics

Length 7–10 in (18–28 cm); weight 6.0–15 oz (180–450 g). The back is nearly uniform cinnamon brown and the face is gray with brown bulging eyes, with a black fine line between the eyes. Ears are large, naked, pink, and membranous. More than half of the tail is furry.

distribution

Venezuela, Trinidad and Tobago, Guyana, Suriname, French Guiana, and Brazil.

habitat

Primary and secondary tropical lowland moist forest in both swampy and well-drained areas, from sea level up to about 2,000 ft (600 m). Rarely, it has also been found in plantations and other agroecosystems. Often found high in the canopy but also rarely seen on the ground or close to it.

behavior

This is a solitary species. The only groups reported are those composed of a female and her suckling young attached to the mammae. Primarily arboreal and rarely abandons the shelter of the high and medium canopy. They are primarily nocturnal and crepuscular, decreasing their activity in periods of high levels of lunar illumination.

feeding ecology and diet

Feeds primarily on fruits but also takes some leaves, insects, bird eggs, and nestlings.

reproductive biology

Polygamous. Females construct nests with plant matter inside hollow trees. After a brief gestation of less than 15 days, one to six young are born blind, naked, and with closed ears. The young crawl to the nipple area, where each attaches to one. There is no well-developed pouch, only lateral folds of skin. Reproduction may occur throughout the year but most frequently at the start of the rainy season.

conservation status

Seems to be dependent on undisturbed tropical moist forest, although it has sometimes been found in secondary vegetation. Destruction of its habitat is the most serious threat. The IUCN lists the species as Lower Risk/Near Threatened.

significance to humans

It is sometimes kept as a pet, and otherwise the species is considered harmful to banana and citrus plantations.

Water opossum

Chironectes minimus

subfamily

Didelphinae

taxonomy

Latra minima (Zimmerman, 1780), Cayenne, French Guiana.

other common names

French: Opossum aquatique; German: Schwimmbeutler; Spanish: Tlacuache de agua, cuica de agua, yapok, zorro de agua, comadreja de agua.

physical characteristics

Length 10.6–15.7 in (27–40 cm); weight 21.2–28 oz (600–790g). Dense and silky hair with four to five broad dark brown bands across the back joined along the dorsal spine. Venter is silvery white and tail is almost naked and scaly. The eyes are large and black, and the face has another dark band across the eyes. The tail is slightly flattened laterally and bicolored, with the distant half whitish. The toes are clearly webbed to aid in swimming.

distribution

Southern Mexico, through Central America, Colombia, Venezuela, Guyana, Suriname, French Guiana, Ecuador, Peru, Brazil, Bolivia, Paraguay, and Argentina.

habitat

Rivers and streams in primary lowland tropical moist forest, generally from sea level up to about 3,300 ft (1,000 m), although it has been found at 6,230 ft (1,900 m).

behavior

A solitary species that swims under water to avoid danger. It is primarily nocturnal, secretive, and silent.

feeding ecology and diet

Feeds mainly on fish, crustaceans, and mollusks. This is the most carnivorous of the New World opossums.

reproductive biology

Polygamous. The female constructs a den on the bank of a river or stream where she builds a nest with vegetation. The young are born very undeveloped after a short gestation. The female keeps the young in a well-developed pouch that closes hermetically when she swims. The male also has a marsupium to protect the testicles.

conservation status

Considered Lower Risk/Near Threatened by the IUCN, but the water opossum has disappeared from many areas in its historical distribution. Deforestation and water pollution are two factors that determine their local extinction.

significance to humans

None known.

Virginia opossum

Didelphis virginiana

subfamily

Didelphinae

taxonomy

Didelphis virginiana Kerr, 1792, Virginia, United States.

other common names

French: Opossum de Virginie; German: Nordopossum; Spanish: Tlacuache común, tlacuache norteño.

physical characteristics

Length 14–21.6 in (35–55 cm); weight 28–176 oz (800–5,000g). Long hair and dense underfur; colors vary from uniform whitish to blackish brown. Ears are black and naked, and cheeks are white. Tail nearly naked, scaly, and bicolored: the basal half is black and the distal half whitish. The feet have opposable thumbs that render their footprints unmistakable.

distribution

Extreme southwestern Canada, the west coast and the eastern half of the United States, tropical and subtropical Mexico, and Central America south to Costa Rica.

habitat

Tropical and temperate forests, in wet and subhumid ecosystems. Found in a wide variety of human-disturbed habitats from logged and secondary forests to agricultural lands and even landfills and urban areas.

behavior

Solitary and nocturnal. Roosts in hollow trees and branches, in leaf litter, crevices and caves under rocks, and in the soil. Feigns death when threatened, gaping its mouth wide and lying on its side while emitting an offensive musky odor.

feeding ecology and diet

Omnivorous. Eats fruit, insects, eggs, small vertebrates, spoiled fruit, carrion, and even trash. Forages at night opportunistically and avoids other medium and large-sized mammals such as raccoons and skunks. It is not a good hunter but rather eats items that are easily available.

reproductive biology

Polygamous. The female builds a nest with leaf litter and vegetation that she transports with the help of the tail. The reproductive season extends from January through July and two birth peaks are reported. After a gestation of about 13 days, as many as 21 young are born undeveloped. Only the first to make it to the pouch are able to survive, as the female has only 13 teats and rarely are all occupied by a young one.

conservation status

Not threatened. Inhabits both pristine and modified ecosystems. They have colonized towns and cities and they are not rare in New York City, Miami, or other large cities. The species does not face any immediate threats of extinction.

significance to humans

Sometimes consumed for food by indigenous or mixed human groups. The species has been pointed out as an agricultural pest or a disease reservoir.

Bushy-tailed opossum

Glironia venusta

subfamily

Didelphinae

taxonomy

Glironia venusta Thomas, 1912, Huánuco, Peru.

other common names

German: Buschschwanzbeutelratten; Spanish: Comadreja de cola peluda, zarigüeya de cola peluda.

physical characteristics

Length 6.3–8.3 in (16–21 cm). The hair on the back is dense and soft, uniformly cinnamon brown. The venter is grayish to brownish white. The tail is long and completely furred with only part of the ventral surface naked, which gives this species its common name. There are two large blackish patches surrounding the eyes, separated by a brown stripe along the top of the snout.

distribution

Eastern Amazonia in western Brazil, Ecuador, Peru, and Bolivia.

habitat

It has been found only in intact lowland tropical moist forest, up to an altitude of 2,600 ft (800 m).

behavior

Not much is known about this species. Considered arboreal on the basis of the specimens found in trees and the morphology of the hand with well-developed grasping abilities.

feeding ecology and diet

Primarily a insectivorous species, but likely it also feeds on fruit, eggs, and small vertebrates.

reproductive biology

Polygamous, but nothing else is known.

conservation status

Considered Vulnerable by the IUCN. Habitat destruction is the primary threat. There is no information on effects of habitat loss.

significance to humans

None known.

Patagonian opossum

Lestodelphys halli

subfamily

Didelphinae

taxonomy

Notodelphys halli (Thomas, 1921), Santa Cruz, Argentina.

other common names

French: Opossum de Patagonie; German: Patagonien-Beutelratten; Spanish: Comadrejita patagónica.

physical characteristics

Length 5–6 in (13–15 cm). The dorsal hair is dense and soft, dark grayish brown with paler sides. Males have an orange patch on the throat. The face is paler than the rest of the body. There are dark patches on shoulders and hips, and the underparts, hands, and feet are white. The tail is clearly shorter than the head and body, and seasonally it appears thick from fat reserves. Tail furry only at the base and covered with fine hairs the rest of its length. Canine teeth are relatively long.

distribution

Occurs in a relatively small region of southern Argentina in the provinces of Río Negro, Neuquén, Santa Cruz, La Pampa, Mendoza, and Chubut.

habitat

It has been reported from the South American steppe grasslands (pampas), and also from shrublands; often associated with streams and other water bodies.

behavior

Seems to be a primarily terrestrial species. It is solitary and active at night.

feeding ecology and diet

A specimen was captured in a trap baited with a dead bird. This species is considered a carnivore but more likely it is insectivorous. Its diet may also include fruit, eggs, and small vertebrates.

reproductive biology

Polygamous, but nothing else is known.

conservation status

The distribution is restricted to a small region of southern Argentina. Classified as Vulnerable. Some portions of its habitat have been modified.

significance to humans

None known.

Thick-tailed opossum

Lutreolina crassicaudata

subfamily

Didelphinae

taxonomy

Didelphis crassicaudata (Desmarest, 1804), Asunción, Paraguay.

other common names

English: Little water opossum; French: Opossum á queue grasse; German: Dickschwanzbeutelratte; Spanish: Comadreja colorada, coligrueso.

physical characteristics

Length 10–16 in (25–40 cm); weight 7–19 oz (200–540 g). The dense, soft, and relatively short hair is uniformly light cinnamon to dark brown and paler below. The legs are relatively short and the body is elongated with a long neck; the ears are short; the tail is long and almost completely furred, except for the ventral surface. There is a well-developed pouch.

distribution

As understood in 2002, the distribution is disjunct, with one population occurring in eastern Colombia, southern Venezuela, and Guyana, and another in eastern Bolivia, northeastern Argentina, southern Brazil, Paraguay, and Uruguay, from an altitude of 1,970–6,560 ft (600–2,000 m).

habitat

Found in lowland and mid-elevation tropical moist forests, grasslands, and shrublands, as well as in forest edges. Always associated with streams and rivers.

behavior

Roosts in hollows in trees, dens of other animals, and nests constructed among the vegetation. An excellent swimmer and

also a good climber, this is a nocturnal species. It is apparently the only species of didelphid that can be accommodated in captivity in small groups, with a weak social structure that permits coexistence of two to three animals.

feeding ecology and diet

Primarily carnivorous, feeding on small vertebrates on land and in the water, as well as crustaceans, insects, and other small animals. An antibothropic biochemical factor has been isolated from its blood, indicating some level of immunity to the venom of snakes.

reproductive biology

Polygamous. Gestation lasts about two weeks. Females give birth to the young in a very undeveloped state. These crawl into the pouch where they attach themselves to a nipple. Births occur twice during the year.

conservation status

Not listed by the IUCN. It seems to be adaptable to a certain degree of disturbance and can be locally common in some areas.

significance to humans

Sometimes considered a nuisance because of its occasional raids on henhouses.

Mexican mouse opossum

Marmosa mexicana

subfamily

Didelphinae

taxonomy

Marmosa murina mexicana Merriam, 1897, Oaxaca, Mexico.

other common names

Spanish: Ratón tlacuache, tacuazín.

physical characteristics

Length 4.7–6.7 in (12–17 cm); weight 0.9–3.2 oz (26–92 g). The back is uniformly reddish brown to grayish brown. The tail, which is prehensile, is about as long as the head and body and 90% of its length is naked. The feet and undersides are paler, sometimes white. There are two large black patches surrounding the large, black eyes. The ears are large, rounded, and naked.

distribution

From eastern and southern Mexico south through central America to western Panama, from sea level up to about 5,900 ft (1,800 m).

habitat

The main habitat is tropical moist forest, but it can also be found in dry tropical forest, secondary forests and disturbed vegetation, and mangrove forests.

behavior

A nocturnal species that is primarily arboreal, although it can also be found on the ground. The mouse opossum readily eats in captivity, quickly attacking and consuming any large insects, eggs, or small vertebrates. It has been found resting inside abandoned hummingbird nests.

feeding ecology and diet

Primarily insectivorous but also eats some fruit, bird eggs, and nestlings, and other prey similar in size.

reproductive biology

Polygamous. Gestation is about 14 days long. The females do not have a marsupium, so the newborn crawl to the mammae and attach themselves to the nipples, which may number from 11 to 15. As they grow larger, the young begin traveling on the mother's back, sometimes curling their tails around hers. Reproductive season extends at least from March through August.

conservation status

The species is not listed by the IUCN. Since it is found in both undisturbed and modified habitats, it probably is not facing major conservation problems.

significance to humans

Sometimes these opossums are kept as pets in rural communities. Some individuals have been found as stowaways in banana shipments to New York City.

Gray slender mouse opossum

Marmosops incanus

subfamily

Didelphinae

taxonomy

Didelphis incana (Lund, 1840), Minas Gerais, Brazil.

other common names

None known.

physical characteristics

Length 4.7–7.9 in (12–20 cm); weight 1–1.9 oz (30–55 g). Dorsal fur is grayish brown to brown and underparts paler. The snout is long and pointed and the ears are large, naked, and pink to brown. There is a patch of black hair around each eye. The tail is long and naked.

distribution

Endemic to eastern Brazil from the state of Bahia to Parana.

habitat

Found in the Atlantic forest of the southeastern coast of Brazil, below 2,640 ft (800 m), in tropical moist forest and deeper inland in somewhat drier forest.

behavior

Nocturnal and crepuscular. Solitary.

feeding ecology and diet

Feeds on insects, eggs, fruit, and small vertebrates.

reproductive biology

Polygamous. A semelparous species in which individuals invest all their effort on a single reproductive event in their lives. Typically, the births occur in a single three-month period around the onset of the rainy season.

conservation status

Considered Lower Risk/Near Threatened by the IUCN. The Atlantic forest of Brazil is one of the most endangered biomes of South America and, if deforestation trends continue, this and other species will face very serious extinction risks.

significance to humans

None known.

Alston's woolly mouse opossum

Micoureus alstoni

subfamily

Didelphinae

taxonomy

Caluromys alstoni (J. A. Allen, 1900), Cartago, Costa Rica.

other common names

French: Souris-opossum laineuse d'Alston; Spanish: Zorricí.

physical characteristics

Length 6.7–7.9 in (17–20 cm); weight 2–5.3 oz (60–150 g). One of the largest mouse opossums. The dorsal hair is yellowish brown to reddish; underparts are paler. Distinct black mask over each eye. The tail is long, slender, and naked. There is no marsupium. The feet have strongly opposable thumbs.

distribution

Caribbean coast of Central America from Belize to Panama and into Colombia, and also in some Caribbean coastal islands.

habitat

Inhabits lowland tropical moist forest and cloud forest below 5,250 ft (1,600 m), and also areas of secondary forest.

behavior

Nocturnal and solitary. Primarily moves in tree canopies and from branch to branch, but can also be found occasionally on the ground.

feeding ecology and diet

Polygamous. Feeds on insects, eggs, fruit, and small vertebrates. Attacks its prey by grasping it with its hands and applying

a series of quick bites all over the body of the prey. Then it is consumed from the head down. Legs and wings of insects are discarded.

reproductive biology

Polygamous. Females build spherical nests with vegetation and debris. After a short gestation of less than two weeks, the young are born in a very undeveloped state. Births have been reported almost in every month of the year. Litter size varies from two to about 14 young.

conservation status

The IUCN classified this species as Lower Risk/Near Threatened. Severe deforestation in Central America is likely having a strong negative impact on this and other species of the region, although it has been found in some protected areas in Costa Rica.

significance to humans

None known.

Red-legged short-tailed opossum

Monodelphis brevicaudata

subfamily

Didelphinae

taxonomy

Didelphis brevicaudata (Erxleben, 1777), Surinam.

other common names

German: Kurzschwanz-Spitzmausbeutelratte; Spanish: Colicorto de patas rojas.

physical characteristics

Length 4.7–7 in (12–18 cm); weight 1.6–3.5 oz (45–100 g). Legs are relatively short as is the tail. Hair is relatively rigid, short, and dense. Color pattern is variable. The back can be dark gray, grizzled with pale hair tips. The sides are rich deep reddish and the change between the gray and red is a very sharp line. Underparts vary from pale, almost white, to light brown. Some individuals are reddish all over the back. The snout is conical, and the ears are rounded, dark, and naked. The tail is relatively short and hairy only at the base and dorsal surface of the basal one-third.

distribution

Venezuela, Guyana, Suriname, French Guiana, and Brazil north of the Amazon river. This species seems restricted to the northern half of the Amazon river basin.

habitat

Tropical moist forest in pristine and modified conditions. Can also be found in orchards and other agroecosystems, but usually upland and away from rivers and streams. It has been found only below 2,620 ft (800 m).

behavior

This is among the few diurnal species in the family. It is also one of the least adapted to climbing and moving in trees; the majority of reports describe it as a terrestrial or strictly terrestrial species.

feeding ecology and diet

Feeds primarily on insects, rodents, birds, eggs, and some fruit. It hunts opportunistically, running and searching through the forest floor under the litter, under logs, and in hollow trees and fallen logs.

reproductive biology

Polygamous. Breeding has been reported almost in every month of the year. Nests are built with plant matter inside or under fallen or hollow logs. The young are born after a gestation of about 15 days. Litters number between five and 12 young. As there is no marsupium, the young are attached to the female's nipples and are dragged under her. As they grow, they begin to travel clinging to their mother's back or sides.

conservation status

This species is not listed by the IUCN. Although it has been found mainly in undisturbed forest, it seems able to survive also in modified forests and agroecosystems.

significance to humans

None known.

Pygmy short-tailed opossum

Monodelphis kunsi

subfamily

Didelphinae

taxonomy

Monodelphis kunsi Pine, 1975, Beni, Bolivia.

other common names

French: Opossum á queue courte de Kuns; German: Kuns-Spitzmausbeutelratte; Spanish: Colicorto pigmeo.

physical characteristics

Length 2.4–3.1 in (6–8 cm); weight 0.6–1.2 oz (18–35 g). The back is uniform yellowish brown with paler underparts. The fur is short and dense. There is a gular gland in males, partially obscured by fur. The tail is short, slender, and almost completely covered with fine, sparse hair, except for its tip. The rostrum is conical and the eyes black. The ears are medium and naked. This is the smallest species in the genus Monodelphis.

distribution

Known only from a few localities in western Brazil and western Bolivia, apparently endemic to the upper Amazon river basin, below 2,100 ft (640 m).

habitat

Tropical moist forest, and maybe also some secondary vegetation.

behavior

Probably solitary. It may also be nocturnal, but almost nothing is known about this species.

feeding ecology and diet

Presumably feeds on insects and other small animals.

reproductive biology

Polygamous, but nothing else is known.

conservation status

Classified by the IUCN as Endangered. Since this is a relatively rare species in nature, and western Amazonia is subject to major deforestation, the species faces serious extinction threats.

significance to humans

None known.

Gray four-eyed opossum

Philander opossum

subfamily

Didelphinae

taxonomy

Didelphis opossum (Linnaeus, 1758), Paramaribo, Surinam.

other common names

French: Opossum á quatre yeux; German: Vieraugenbeutelratte; Spanish: Tlacuache cuatro ojos, zorro cuatro ojos, comadreja cuatro ojos.

physical characteristics

Length 8–13 in (20–33 cm); weight 7–24.7 oz (200–700 g). This relatively large opossum has dense and relatively short hair that varies from pale gray to dark gray dorsally and yellowish white ventrally. The cheeks and chin are also yellowish white, as are two conspicuous spots just above the eyes, which give this species its common name. The ears are large and naked, blackish with pink bases. There is a marsupial pouch that stains orange if the female has had young. The tail in most individuals is bicolored with the base dark and the final third to half white, naked, and scaly except the basal 0.8 in (2 cm), which are furred.

distribution

From eastern and southern Mexico south through Central America and into South America to Bolivia, Paraguay, northeastern Argentina, and southeastern Brazil.

habitat

Inhabits dense tropical moist forests, secondary areas, orchards, and other agricultural and modified ecosystems. It has been recorded from sea level up to about 5,400 ft (1,650 m). It is most abundant near streams, rivers, and other water bodies.

behavior

When threatened, it hisses and gasps, snapping at the intruder. This is a mostly nocturnal species but sometimes may be active by day. Although most of the time it stays on the ground, it may also climb into trees. Like other didelphids, gray four-eyed opossums are solitary. When it is asleep, it rolls into a ball and the eyes are not visible, but the bright spots above the eyes give the appearance of an awake and alert opossum.

feeding ecology and diet

The four-eyed opossum is omnivorous. It feeds on many species of tropical and introduced fruits, corn, palm fruits, flower nectar, frogs, birds, rodents, and other small vertebrates, snails, insects, crustaceans, and carrion. Insects are most frequently eaten in the dry season. They tend to take fruits that are larger than 2 in (5 cm) in diameter and that are fleshy, juicy, with high contents of sugars or lipids, and low levels of nitrogen.

reproductive biology

Polygamous. Breeds throughout the year or seasonally, depending on the region. Females have seven mammae. Although there may be more babies born than this number, a maximum of seven can be found in the pouch. Females may have more than one birth per year. They construct a nest of litter and other vegetation in tree limbs, in hollows in standing or fallen trees, or in dens underground. The nest is spherical and about 11.8 in (30 cm) in diameter. Litters of one to seven with an average of about five are reported. Females are sexually receptive when they are seven months old. Maximum longevity is about 2.5 years in the wild and 3.5 years in captivity.

conservation status

This is generally an abundant species that can live in both pristine and disturbed conditions. It can also live in houses in rural areas. The IUCN has not listed it, and it does not seem to be threatened.

significance to humans

Sometimes considered a nuisance because it may raid henhouses. This species and other didelphids are reservoirs of Trypanosoma cruzi, the protozoan that causes Chagas' disease.

Resources

Books

Benton, M. J. The Rise of the Mammals. New York: Crescent Books, 1991.

Collins, L. Monotremes and Marsupials. Washington, DC: Smithsonian Institution Press, 1973.

Eisenberg, J. F. Mammals of the Neotropics. Vol.1, The Northern Neotropics. Chicago: University of Chicago Press, 1990.

Eisenberg, J. F., and K. H. Redford. Mammals of the Neotropics. Vol. 3, The Central Neotropics. Chicago: University of Chicago Press, 1999.

Hunsaker II, D. The Biology of Marsupials. New York: Academic Press, 1977.

Nowak, R. M. Walker's Mammals of the World. 6th ed., Vol. 1, Baltimore: John Hopkins University Press, 1999.

Redford, K. H., and J. F. Eisenberg. Mammals of the Neotropics. Vol. 2, The Southern Cone. Chicago: University of Chicago Press, 1992.

Wilson, D. E., and D. M. Reeder. Mammal Species of the World. Washington: Smithsonian Institution Press, 1993.

Periodicals

Alonso-Mejía, A., and R. A. Medellín. "Marmosa mexicana." Mammalian Species 421 (1992): 1–4.

Caceres, N. C. "Food Habits and Seed Dispersal by the White-eared Opossum, Didelphis albiventris, in Southern Brazil." Studies on Neotropical Fauna and Environment 37 (2002): 97–104.

Castro, I., H. Zarza, and R. A. Medellín. "Philander opossum." Mammalian Species 638 (2000): 1–8.

Lemos, B., G. Marroig, and R. Cerqueira. "Evolutionary Rates and Stabilizing Selection in Large-bodied Opossum Skulls (Didelphimorphia: Didelphidae)." Journal of Zoology 255 (2001): 181–189.

Marshall, L. G. "Chironectes minimus." Mammalian Species 109 (1978): 1–6.

——. "Glironia venusta." Mammalian Species 107 (1978): 1–3.

——. "Lestodelphys halli." Mammalian Species 81 (1977): 1–3.

McManus, J. J. "Didelphis virginiana." Mammalian Species 40 (1974): 1–6.

Medellín, R. A. "Seed Dispersal of Cecropia obtusifolia by Two Species of Opossums." Biotropica 26 (1994): 400–407.

Rodrigo A. Medellín, PhD