The Giant Fossa (Cryptoprocta spelea) 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. It was first described in 1902, and in 1935 was recognized as a separate species from its closest relative, the living fossa (Cryptoprocta ferox). C. spelea is larger than the fossa, but otherwise similar. The two have not always been accepted as distinct species. It was hunted to extinction by humans when they began to settle on the island of Madagascar.
The species is known from subfossil bones found in a variety of caves in northern, western, southern, and central Madagascar. In some sites, it occurs with remains of C. ferox, but there is no evidence that the two lived at the same time. 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. The giant fossa may have had the ability to prey on bigger animals, such as the extinct giant lemurs.