Fossas are cat-like Madagascan carnivores in the family Viverridae, which also includes civets, linsangs, genets, and mongooses. Fossas are quite different from other viverrids and are the sole members of the subfamily Cryptoproctinae. They are the largest Madagascan carnivores, measuring 24-30 in (60-75 cm) long. With a number of cat-like features-including a rounded head, long whiskers, large frontal eyes, middle-sized roundish ears, and relatively short jaw-led to its original classification as a felid. However, the fossa's resemblance to cats is superficial and a result of convergent evolution.
The neck of the fossa is short and thickset, and its body is muscular, long, and slender. The legs are short, and its sharp, curved, retractile claws help it climb trees. The long tail of the fossa is used for balance, but is not prehensile. The feet support well-developed hairless pads which help secure the footing. The fossa is planti-grade, meaning it walks upon the whole foot rather than just the toes, as in most viverrids. The fur is short, thick, and reddish brown on the upperside; the underside is lighter. Occasionally, the fossa is melanistic (an increased amount of nearly black pigmentation.) Fossas are nocturnal terrestrial and arboreal predators, living primarily in coastal forests, and are rarely seen in the central highlands of Madagascar. Their home range is several square kilometers depending on the type of country. The fossa is territorial, marking upright objects within its boundaries with oily secretions from the anal and preputial (loose skin covering the penis) glands. Possessing excellent hearing, sight, and scent, along with having no natural enemies, the fossa is the most powerful predator in Madagascar. Possessing 32 sharp teeth, the fossa has a varied diet including civets and young bush-pigs and other mammals up to the size of lemurs, birds up to the size of guinea fowl, eggs, lizards, snakes, frogs, and insects. Additionally, it will prey on domestic poultry, rabbits, and sheep.
Fossas are solitary, except during the breeding season in September and October, when the nocturnal habits of the fossa also change slightly and become diurnal. After a three-month gestation, two to four young are born in burrows, among rocks, in holes in trees, or forks at the base of large boughs. Only the female fossa will rear the young. The newborn are quite small when compared with other viverrids, and their physical development is slow. The eyes do not open for 16-25 days. The first milk tooth appears when the young fossa is ready for the inaugural venture from the nest at one and a half months. Though weaned by four months, solid food is not taken until three months of age. Climbing begins at about three and a half months. Fully grown and independent at two years, the fossa does not reach sexual maturity for another two years. Male fossa possess a penis-bone, called a baculum. Females exhibit genital mimicry of the males, though the mimicry is not well developed.
Grooming techniques are similar to felids, with licking and scratching with the hind feet, and face washing with the fore feet. Fossas display a variety of vocalizations: a short scream repeated five to seven times is a threat, while the mating call of the female is a long mew, lasting up to 15 seconds. The female calls the young with a sharp, long whimpering. When first beginning to suckle, the young will growl, and both sexes mew and growl when mating.
Fossas live in low population densities and require undisturbed forests which are unfortunately rapidly disappearing on the heavily logged island of Madagascar. Though fossas have lived as long as 17 years in captivity, these animals are unlikely to survive as long in the wild. Recognition of fossas as endangered species is likely.
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Betsy A. Leonard