The American representatives of the marsupials
Opossums are the American representatives of the marsupials, which have one of the strangest methods of mammalian reproduction. Newborn, which look like tiny embryos, crawl form the birth canal through the mother's fur into a pouch containing the teats. Here, the young latch onto a nipple and complete most of their development.
The first marsupial seen in Europe was an opossum, brought home by the Spanish explorer Pinzón in the 16th century. Male opossums have a forked penis, and early naturalist thought that the animals copulated through the nose and the mother then blew the embryo into the pouch! Gestation is 12 days, followed by two month in the pouch.
Nine of approximately 70 opossum species are found in Costa Rica. the most frequently seen is the common opossum (zorro pelón; Didelphis marsupialis. Resembling overgrown, long legged rats, they reach almost a meter in length, of which the tail is almost half. Adults weigh 0.6 to 1.8kg, although there have been reports of some reaching 5kg! Males are larger than females. the back and legs are blackish brown or gray and the head and under parts light brown or yellowish, with much variation in color due to the coarse, two-layered fur.
They are mainly nocturnal, often seen foraging for anything edible along watercourses and in garbage dumps. Distribution is nationwide, but normally below 1500m. They are both terrestrial and arboreal and, when cornered, will hiss and attempt to bite, rather than pretending to lie dead, as the North American opossums do.
A smaller species seen quite often is the gray four eyed opossum (Philander opossum) found in rainforest regions and recognized by the black face mask with large white spots over the eyes, and a grayer, smoother appearance than the previous species. The water opossum (Chironectes minimus) is locally common on some rivers and has a light /dark-grey-striped pattern in its back.