The fossa (Cryptoprocta ferox; /ˈfɒsə/ FOSS-ə or /ˈfuːsə/ FOO-sə;[3] Malagasy: [ˈfusə̥]) is a slender, long-tailed, cat-like mammal that is endemic to Madagascar.

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.

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.

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.

However, an alternative etymology suggests a link to another word that comes from Malay: pusa refers to the Malayan weasel (Mustela nudipes).

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.

[4][10] 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.

[10] 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.

[1] 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.

[4][14][15] (other feliforms) Viverridae (civets, genets, and their relatives) Hyaenidae (hyenas) Herpestidae (mongooses) Eupleridae (Malagasy carnivores) C. ferox (Fossa) †C.

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.

[4] 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.

[20] 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.

[25] The presence of the fossa at these locations indicates its ability to adapt to various elevations, consistent with its reported distribution in all Madagascar forest types.

[4][9] Throughout the year, animals produce long-lasting scent marks on rocks, trees, and the ground using glands in the anal region and on the chest.

[9][29] Although it is the predominant predator of lemurs,[29][30] reports of its dietary habits demonstrate a wide variety of prey selectivity and specialization depending on habitat and season; diet does not vary by sex.

While the fossa is thought to be a lemur specialist in Ranomafana National Park,[31] its diet is more variable in other rain forest habitats.

[15] In a study of fossa diet in the dry deciduous forest of western Madagascar, more than 90% of prey items were vertebrates, and more than 50% were lemurs.

[15] The fossa is known to eviscerate its larger lemur prey, a trait that, along with its distinct scat, helps identify its kills.

[4] This wide variety of prey items taken in various rainforest habitats is similar to the varied dietary composition noted[23][25] occurring in the dry forests of western Madagascar, as well.

[20] This unusually lengthy mating is due to the physical nature of the male's erect penis, which has backwards-pointing spines along most of its length.

Recent research suggests that this system helps the fossa overcome factors which would normally impede mate-finding, such as low population density and lack of den use.

[36] The birthing of the litter of one to six[17] (typically two to four)[4] takes place in a concealed location, such as an underground den, a termite mound, a rock crevice, or in the hollow of a large tree[15] (particularly those of the genus Commiphora).

[9][15] A suite of microsatellite markers (short segments of DNA that have a repeated sequence) have been developed to help aid in studies of genetic health and population dynamics of both captive and wild fossas.

The loss of the fossa, either locally or completely, could significantly impact ecosystem dynamics, possibly leading to over-grazing by some of its prey species.

[40] In the Marolambo District (part of the Atsinanana region in Toamasina Province), the fossa has traditionally been hated and feared as a dangerous animal.

[39] However, the animal is also taken for bushmeat;[15] a study published in 2009 reported that 57 percent of villages (8 of 14 sampled) in the Makira forest consume fossa meat.

[41] Near Ranomafana National Park, the fossa, along with several of its smaller cousins and the introduced small Indian civet (Viverricula indica), are known to "scavenge on the bodies of ancestors", which are buried in shallow graves in the forest.

[16] The fossa was depicted as an antagonist in the 2005 DreamWorks animated film Madagascar, being referred to as the "foosa", and accurately shown as the lemurs' most feared predator.