The fossa (Cryptoprocta ferox; or ; ) is a slender, long-tailed, cat-like mammal that is endemic to Madagascar. It is a member of the carnivoran family Eupleridae.
The fossa is the largest mammalian carnivore on Madagascar and has been compared to a small cougar, as it has convergently evolved many cat-like features. Adults have a head-body length of and weigh between , with the males larger than the females. It has semi-retractable claws (meaning it can extend but not retract its claws fully) and flexible ankles that allow it to climb up and down trees head-first, and also support jumping from tree to tree. Two larger extinct relatives of the species are known, Cryptoprocta spelea and Cryptoprocta bevatabe, with the former probably becoming extinct before 1400.
The species is widespread, although population densities are usually low. It is found solely in forested habitat, and actively hunts both by day and night. Over 50% of its diet consists of lemurs, the endemic primates found on the island; tenrecs, rodents, lizards, birds, and other animals are also documented as prey. Mating usually occurs in trees on horizontal limbs and can last for several hours. Litters range from one to six pups, which are born altricial (blind and toothless). Infants wean after 4.5 months and are independent after a year. Sexual maturity occurs around three to four years of age, and life expectancy in captivity is 20 years. The fossa is listed as a vulnerable species on the IUCN Red List. It is generally feared by the Malagasy people and is often protected by their fady taboo. The greatest threat to the fossa is habitat destruction.
Its taxonomic classification has been controversial because its physical traits resemble those of cats, yet other traits suggest a close relationship with viverrids. Its classification, along with that of the other Malagasy carnivores, influenced hypotheses about how many times mammalian carnivores have colonized Madagascar. With genetic studies demonstrating that the fossa and all other Malagasy carnivores are most closely related to each other forming a clade, recognized as the family Eupleridae, carnivorans are now thought to have colonized the island once, around 18–20 million years ago.
Etymology The generic name Cryptoprocta refers to how the animal's anus is hidden by its anal pouch, from the Ancient Greek words crypto- "hidden", and procta "anus". The species name ferox is the Latin adjective "fierce" or "wild". Its common name comes from the word fosa in Malagasy, an Austronesian language, and some authors have adopted the Malagasy spelling in English.
The word is similar to posa (meaning "cat") in the Iban language (another Austronesian language) from Borneo, and both terms may derive from trade languages from the 1600s. However, an alternative etymology suggests a link to another word that comes from Malay: pusa refers to the Malayan weasel (Mustela nudipes). The Malay word pusa could have become posa for cats in Borneo, while in Madagascar the word could have become fosa to refer to the fossa.
Taxonomy The fossa was formally described by Edward Turner Bennett on the basis of a specimen from Madagascar sent by Charles Telfair in 1833. The common name is the same as the generic name of the Malagasy civet (Fossa fossana), but they are different species. Because of shared physical traits with viverrids, mongooses, and Felidae, its classification has been controversial. Bennett originally placed the fossa as a type of civet in the family Viverridae, a classification that long remained popular among taxonomists. Its compact braincase, large eye sockets, retractable claws, and specialized carnivorous dentition have also led some taxonomists to associate it with the felids. In 1939, William King Gregory and Milo Hellman placed the fossa in its own subfamily within Felidae, the Cryptoproctinae. George Gaylord Simpson placed it back in Viverridae in 1945, still within its own subfamily, yet conceded it had many cat-like characteristics.
In 1993, Géraldine Veron and François Catzeflis published a DNA hybridization study suggesting that the fossa was more closely related to mongooses (family Herpestidae) than to cats or civets. However, in 1995, Veron's morphological study once again grouped it with Felidae. In 2003, molecular phylogenetic studies using nuclear and mitochondrial genes by Anne Yoder and colleagues showed that all native Malagasy carnivorans share a common ancestry that excludes other carnivores (meaning they form a clade, making them monophyletic) and are most closely related to Asian and African Herpestidae. To reflect these relationships, all Malagasy carnivorans are now placed in a single family, Eupleridae. Within Eupleridae, the fossa is placed in the subfamily Euplerinae along with the falanouc (Eupleres goudoti) and Malagasy civet, but its exact relationships are poorly resolved.
An extinct relative of the fossa was described in 1902 from subfossil remains and recognized as a separate species, Cryptoprocta spelea, in 1935. This species was larger than the living fossa (with a body mass estimate of around 10-20 kg), but otherwise similar. An even larger extinct species, Cryptoprocta bevatabe, was described in 2026. Robustly-built and with greater derivity in its climbing adaptations, it was Madagascar's largest terrestrial mammalian carnivore (with a body mass of around 27-43 kg). Across Madagascar, people distinguish threes kinds of fossa—a large fosa mainty ("black fossa"), a mid-sized fosa ondry ("off-white fossa"), and the small fosa mena ("reddish fossa"). It is unclear whether this is purely folklore or individual variation—related to sex, age or instances of melanism and leucism—or whether there is indeed more than one species of living fossa.
Description
The fossa appears as a diminutive form of a large felid, such as a cougar, but with a slender body and muscular limbs, and a tail nearly as long as the rest of the body. It has a mongoose-like head, relatively longer than that of a cat, although with a muzzle that is broad and short, and with large but rounded ears. It has medium brown eyes set relatively wide apart with pupils that contract to slits. Like many carnivorans that hunt at night, its eyes reflect light; the reflected light is orange in hue. Its head-body length is and its tail is long. There is some sexual dimorphism, with adult males (weighing ) being larger than females (). Smaller individuals are typically found north and east on Madagascar, larger ones to the south and west. Unusually large individuals weighing up to have been reported, but there is some doubt as to the reliability of the measurements. The fossa can smell, hear, and see well. It is a robust animal and illnesses are rare in captive fossas.
Both males and females have short, straight fur that is relatively dense and without spots or patterns. Both sexes are generally a reddish-brown dorsally and colored a dirty cream ventrally. When in rut, they may have an orange coloration to their abdomen from a reddish substance secreted by a chest gland, but this has not been consistently observed by all researchers. The tail tends to be lighter in coloration than the sides. Juveniles are either gray or nearly white.
Several of the animal's physical features are adaptions to climbing through trees. It uses its tail to assist balance and has semi-retractable claws that it uses to climb trees in its search for prey. It has semiplantigrade feet, switching between a plantigrade-like gait (when arboreal) and a digitigrade-like one (when terrestrial). The soles of its paws are nearly bare and covered with strong pads. The fossa has very flexible ankles that allow it to readily grasp tree trunks so as to climb up or down trees head first or to leap to another tree. Captive juveniles have been known to swing upside down by their hindfeet from knotted ropes.
The fossa has several scent glands, although the glands are less developed in females. Like herpestids it has a perianal skin gland inside an anal sac which surrounds the anus like a pocket. The pocket opens to the exterior with a horizontal slit below the tail. Other glands are located near the penis or vagina, with the penile glands emitting a strong odor. Like the herpestids, it has no prescrotal glands.
External genitalia
One of the more peculiar physical features of this species is its external genitalia. The fossa is unique within its family for the shape of its genitalia, which share traits with those of cats and hyenas. The male fossa has an unusually long penis and baculum (penis bone), reaching to between his forelegs when erect, with an average thickness of . The glans extends about halfway down the shaft and is spiny except at the tip. In comparison, the glans of felids is short and spiny, while that of viverrids is smooth and long. The female fossa exhibits transient masculinization, starting at about 1–2 years of age, developing an enlarged, spiny clitoris that resembles a male's penis. The enlarged clitoris is supported by an os clitoridis, which decreases in size as the animal grows. The females do not have a pseudo-scrotum, but they do secrete an orange substance that colors their underparts, much like the secretions of males.
Hormone levels (testosterone, androstenedione, dihydrotestosterone) do not seem to play a part in this transient masculinization, as those levels are the same in masculinized juveniles and non-masculinized adults. It is speculated that the transient masculinization either reduces sexual harassment of juvenile females by adult males, or reduces aggression from territorial females. While females of other mammal species (such as the spotted hyena) have a pseudo-penis, no other is known to diminish in size as the animal grows.
Comparison with related carnivorans Overall, the fossa has features in common with three different carnivoran families, leading researchers to place it and other members of Eupleridae alternatively in Herpestidae, Viverridae, and Felidae. Felid features are primarily those associated with eating and digestion, including tooth shape and facial portions of the skull, the tongue, and the digestive tract, typical of its exclusively carnivorous diet. The remainder of the skull most closely resembles skulls of genus Viverra, while the general body structure is most similar to that of various members of Herpestidae. The permanent dentition is (three incisors, one canine, three or four premolars, and one molar on each side of both the upper and lower jaws), with the deciduous formula being similar but lacking the fourth premolar and the molar.
The fossa has a large, prominent rhinarium similar to that of viverrids, but has comparatively larger, round ears, almost as large as those of a similarly sized felid. Its facial vibrissae (whiskers) are long, with the longest being longer than its head. Like some mongoose genera, particularly Galidia (which is now in the fossa's own family, Eupleridae) and Herpestes (of Herpestidae), it has carpal vibrissae as well. Its claws are retractile, but unlike those of Felidae species, they are not hidden in skin sheaths. It has three pairs of nipples (one inguinal, one ventral, and one pectoral).
Habitat and distribution