The coelacanths constitute a rare order of fish that includes two extant species. They follow the oldest known living lineage of lobe-finned fish and tetrapods, which means they are more closely related to lungfish, reptiles and mammals than to the common ray-finned fishes. In modern times, they are found along the coastlines of the Indian Ocean and Indonesia.
Coelacanths belong to the subclass Actinistia, a group of lobed-finned fish related to lungfish and certain extinct Devonian fish. Coelacanths were thought to have become extinct in the Late Cretaceous, around 66 million years ago, but were rediscovered in 1938 off the coast of South Africa.
The coelacanth was long considered a “living fossil” because it was believed to be the sole remaining member of a taxon otherwise known only from fossils, with no close relations alive, and to have evolved into roughly its current form approximately 400 million years ago. However, several recent studies have shown that coelacanth body shapes are much more diverse than previously thought.