Didelphidae

The didelphids (Didelphidae) are a family of marsupial mammals, the only one with currently living species within the order Didelphimorphia, with a total of 92 species. They have lived since the Upper Cretaceous.

The family includes species native to America that are generally of medium size and have both terrestrial and arboreal habits. They are distinguished by their long snout, their oblong skull, a bony crest running longitudinally down the center of the skull, and unspecialized teeth.

Unusually among non-primate mammals, they have an opposable toe on their hind feet with a nail, not a claw. They have a prehensile tail, which helps them move on the branches, and is used by juveniles to cling to the mother's body.

Ecology

They colonize most of the ecosystems of the neotropical region, from grasslands and bushy areas to tropical jungle, and from sea level to 3000 meters of altitude, and as a general rule they are at least partially arboreal, with the exception of the yapok (Chironectes minimus), with basically aquatic habits.

Phaneroptics and anatomy

Didelphids are small or medium-sized animals with a relative morphological resemblance between the different species that make up the family that hardly present significant differences with respect to their Cretaceous ancestors.

The incisors of the upper jaw are conical, small, and unequal. The first pair is larger than the rest of which are separated. The canines are large, and the molars are trituberculate. The dental formula of these animals is as follows:

The facial region of the skull is large, long, and pointed, while the braincase is relatively small. Inside it is a brain with defined lobes and few cortical gyri.

The sagittal crest is well defined and highly developed in most of the genera of the family.

The head is elongated, with a pointed snout and ears with rounded, very evident pinnae.

The limbs are short, the hind limbs slightly longer than the forelimbs. Hands and feet have five fingers without syndactyly phenomena as in other metatherians, but the first finger of the hind limbs is larger and partially opposable to the rest, also lacking a claw, in whose place there is a nail.

The tail is usually long, scaly and prehensile, although these characteristics are not common to all species.

Physiology and nutritional habits

Tremendously opportunistic, these marsupials feed on a large amount of resources of both animal and plant origin, although there are tendencies for certain food groups depending on the species, geographic location, or weather season.

As a general rule, they are good hunters, the largest species being able to have the largest animals among their prey. Small mammals, birds, reptiles, and amphibians are among their foods. Insects and other arthropods, earthworms, molluscs and other invertebrates are also part of their diet, which they supplement with plant products such as fruits, nectar or grain.

Many of the species also have scavenging habits.

Biology and reproductive behavior

The gestation period, as in all marsupials, is short, usually not exceeding two weeks. At the end of them, sparsely developed pups are born in which the well-formed forelimbs and endowed with fingernails attract attention, essential for clinging to the skin of the abdomen, especially in those genera in which the marsupium is reduced to two skin folds that run longitudinally on both sides of the abdominal and pelvic region, as it is only well developed in the genera Chironectes, Didelphis and Philander< /i>.

Behavior

They are nocturnal or crepuscular animals.

Aggressive, reclusive and solitary, they only interact with other conspecifics during the mating season (male-female) or the breeding season (mother-offspring).

It is notable in some representatives of this family the habit of pretending to be dead when they are in danger and cannot escape from the aggressors who dare to confront an animal with such an aggressive appearance as the one shown by a harassed opossum.

With this appearance, it is difficult to distinguish them from truly dead bodies, although performing an electroencephalogram on them has confirmed the alert state in which the living animal is found.

There are species that tend to play dead as referred to by the scholar Professor Daniel Lòpez M. in his books, they reach the limit of not letting their heartbeats be felt, which are only perceptible with the application of ECG (electro cardiogram). This behavior is not voluntary and seems to be a defense mechanism in extreme situations.

Ecological paper

Although the conservation status of many of the species currently alive is not known, many of them enjoy the privilege of being classified as least concern (LR/lc) by the IUCN.

However, some of them, such as the Bolivian graceful marmosa (Gracilinanus aceramarcae), Anderson's marmosa (Marmosa andersoni), Handley's slender marmosa (< i>Marmosops handleyi), the dryland marmosa (Marmosa xerophila), the slender carifina marmosa (Marmosops cracens) or the pygmy shorttail (Monodelphis kunsi) are threatened (EN), being critical (CR) in the case of the first three.

They are found at an intermediate level of the trophic chain, so their relationship with other animal species depends notably on this fact. Large carnivores and nocturnal raptors are among its main predators.

In another time they were hunted for the use of their skins, today devalued. At present, hunting is aimed at many of the areas where they are distributed for the use of their meat, which looks and tastes similar to chicken.

Some species do not rule out approaching populated areas, especially agricultural areas, being persecuted for the damage they cause to plantations.

However, and although some of these marsupials, such as those of the genus Didelphis, are carriers of Trypanosoma cruzi, the protozoan that causes Chagas disease, it is necessary to take into account the great benefit they represent with respect to the presence of pests, controlling the populations of rodents and arthropods, much more harmful than the possums themselves.

Some species within this family are used as laboratory animals.

They are retracting their territory as rats increasingly invade their territories, the latter being more efficient and competitive. Generally we can say that finding mucas in a field area is finding a clean area, the opposite is a sign of contamination.