Cryptoprocta spelea, also known as the giant fossa,[4] is an extinct species of carnivore from Madagascar in the family Eupleridae which is most closely related to the mongooses and includes all Malagasy carnivorans.

When and how C. spelea became extinct is unknown; there is some anecdotal evidence, including reports of very large fossas, that there is more than one surviving species.

Living species of comparably sized, related carnivores in other regions manage to coexist, suggesting that the same may have happened with both C. spelea and C. ferox.

[10] Lamberton recognized a third species, Cryptoprocta antamba, on the basis of a mandible (lower jaw) with abnormally broad spacing between the condyloid processes at the back.

[12] The specific name refers to the "antamba", an animal allegedly from southern Madagascar described by Étienne de Flacourt in 1658 as a large, rare, leopard-like carnivore that eats men and calves and lives in remote mountainous areas;[13] it may have been the giant fossa.

[15] Together, the fossa and C. spelea form the genus Cryptoprocta within the family Eupleridae, which also includes the other Malagasy carnivorans—the falanouc, the fanalokas, and the Galidiinae.

DNA sequence studies suggest that the Eupleridae form a single natural (monophyletic) group and are most closely related to the mongooses of Eurasia and mainland Africa.

[23] Subfossil remains of the giant fossa have been found in Holocene cave sites[3] from the northern end of Madagascar along the west coast to the far south, and in the central highlands.

[27] No subfossil evidence has been found to definitively show that lemurs were its prey; this assumption is based on the diet of the smaller, extant species of fossa.