Fossa facts: Its name derived from a native Malagasy word, and pronounced “foosh,” this puzzling animal is as worthy of biodiversity poster status as the more famous lemurs of Madagascar.
The fossa is the largest of all mongoose species, with an adult headand-body length of 24 to 31.5 inches (61 to 80 centimeters), a tail as long as the head and body, and an adult weight of eleven to twenty pounds (5 to 10 kilograms). A fossa looks like a combination of dog, cat, and mongoose, and has retractable claws, like a cat’s, something not seen in other mongoose species. If approaching head-on, a fossa gives the impression of a scaled-down puma, but a side view shows the snout to be longer than that of the true cats, but shorter and wider than the norm among mongoose species. The gray-brown nostril pad is furless and prominent, like a dog’s. The overall appearance and behavior suggests a cat rather than a dog.
The body is long and sleek and the legs are short but powerful, as in a mongoose. The coat color is rich reddish-brown, the undersides lighter but stained with an orange secretion from skin glands. This secretion is more abundant in males than in females. There are five padded digits on each of the four feet. Though its movements are often considered plantigrade, meaning that the entire foot, from the toetips to the back of the heel, touch the ground when walking, fossas have also been seen to walk digitigrade, that is, only on the toetips. The large, prominent eyes are brown and lustrous, and have pupils that can retract to vertical slits, as in cats. The ears are large, prominent, and narrower than in typical mongoose species.
The fossa was originally classified as a direct descendant, little changed, of the ancestor species that gave rise to cats (Felidae) and dogs (Canidae). That classification arose from both to the appearance of the fossa and to the notion that Madagascar was a natural refuge for primitive mammal species driven to extinction elsewhere by more advanced species. At the same time, the fossa is the living creature closest in form to the dog-cat ancestor. Its classification is still uncertain. Genetic comparison studies strongly support the fossa and the other Malgasy mammal carnivores as being descendants, having changed forms over the ages through adaptive evolution, of a single colonizing species of mongoose. The founder species must have floated from Africa to Madagascar twenty to thirty million years ago. The fossa is the end result of adaptive evolution by which a mongoose, over countless generations, became something like a cat. At the same time, the fossa keeps a number of mongoose-like features. Scientists have found remains of a larger species related to the fossa, since named Cryptoprocta spelea.
Geographic range: Fossas live in all of the forested areas of Madagascar.
Fossa habitat: Fossas live in the humid tropical rainforests of Madagascar’s east coast and the drier forests along its western coast.
What does fossa eat: The fossa is carnivorous and able to deal with nearly all sorts of small to large prey animals on Madagascar, including the larger lemur species, which can be bigger than house cats. Fossas also prey upon snakes, tenrecs (native insectivorous mammals of Madagascar), and rodents, most often introduced rats. Fossas only rarely feed on insects and other invertebrates.
Behavior and reproduction: Fossas hunt at any time of night or day. They can swim and are adept at climbing and jumping among trees while chasing prey. The animals can turn their ankles so that their hindfeet face rearward, a unique adaptation that aids them in keeping a grip on treetrunks. The long tail acts as a balance while the fossa climbs or jumps between trees. Fossas hunt alone, or in family groups made up of a mother and her young.
There is a single annual mating season from October into December. Gestation lasts six to seven weeks. Litters number two to four young. Fossa young are very cute and endearing. They have big ears and eyes, their faces suggest a combination of domestic kitten, puppy, and lion cub, and they stare out at the world with the intent, slightly bewildered stare of young domestic kittens.
Mating is a complex affair, resembling that of cats. A female in heat stations herself in a tree, while several males, following her scent, gather around the tree, vocalizing and fighting among themselves. Then, one at a time, the males climb the tree and are accepted or rejected by the female. If she accepts a male, she will usually walk farther out on a branch but allow the male to mount her from behind, his forepaws resting on her neck, while he gently grips the female’s nape in his jaws. A single mating can last for several hours, and the female will mate with several of the gathered males.
Only the mother raises the young, in a tree hollow or a hollowedout termite nest. The young of both sexes reach sexual maturity at four years. A most interesting phenomenon among female fossa young is that they pass through a brief pseudo-masculine stage in their second year, during times of becoming less dependent on the mother and reaching sexual maturity. Their genitals come to resemble those of an adult male, they leave ano-genital scent markings on objects, as do adult males (adult females do not, except in mating season), and the female young secrete more of the fur-staining orange fluid than do adult females. Why this occurs is unanswered, and the young females lose the masculine characteristics as they approach sexual maturity.
Fossas have been known to live for twenty years in captivity.
Fossas and people: The fossa has not fared well with humans in Madagascar. Fossas raid chicken coops, leaving resentment behind, and an aura of superstitious fear surrounds them.
Conservation status: The fossa is listed as Endangered by the IUCN. Although widespread throughout Madagascar, the fossa’s population density and total population are low, making it especially vulnerable to deforestation, which is ongoing and rampant in Madagascar.