Coelacanth

The coelacanths (/ˈsiːləkænθ/ (listen) SEE-lə-kanth) constitute a now-rare order of fish that includes two extant species in the genus Latimeria: the West Indian Ocean coelacanth (Latimeria chalumnae) primarily found near the Comoro Islands off the east coast of Africa and the Indonesian coelacanth (Latimeria menadoensis). They follow the oldest-known living lineage of Sarcopterygii (lobe-finned fish and tetrapods), which means they are more closely related to lungfish and tetrapods than to ray-finned fishes. They are found along the coastlines of the Indian Ocean and Indonesia. The West Indian Ocean coelacanth is a critically endangered species. Coelacanths belong to the subclass Actinistia, a group of lobed-finned fish related to lungfish and certain extinct Devonian fish such as osteolepiforms, porolepiforms, rhizodonts, and Panderichthys. 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 scientists thought it was the sole remaining member of a taxon otherwise known only from fossils, with no close relations alive, and that it 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. The word Coelacanth is an adaptation of the Modern Latin Cœlacanthus ('hollow spine'), from the Greek κοῖλ-ος (koilos 'hollow' + ἄκανθ-α akantha 'spine'). It is a common name for the oldest living line of Sarcopterygii, referring to the hollow caudal fin rays of the first fossil specimen described and named by Louis Agassiz in 1839. The genus name Latimeria commemorates Marjorie Courtenay-Latimer who discovered the first specimen in a fish market. The coelacanth, which is related to lungfishes and tetrapods, was believed to have been extinct since the end of the Cretaceous period. More closely related to tetrapods than to the ray-finned fish, coelacanths were considered transitional species between fish and tetrapods. On 23 December 1938, the first Latimeria specimen was found off the east coast of South Africa, off the Chalumna River (now Tyolomnqa). Museum curator Marjorie Courtenay-Latimer discovered the fish among the catch of a local angler, Captain Hendrick Goosen. Latimer contacted a Rhodes University ichthyologist, J. L. B. Smith, sending him drawings of the fish, and he confirmed the fish's importance with a famous cable: 'MOST IMPORTANT PRESERVE SKELETON AND GILLS = FISH DESCRIBED.' Its discovery 66 million years after it was believed to have become extinct makes the coelacanth the best-known example of a Lazarus taxon, an evolutionary line that seems to have disappeared from the fossil record only to reappear much later. Since 1938, West Indian Ocean coelacanth have been found in the Comoros, Kenya, Tanzania, Mozambique, Madagascar, and in iSimangaliso Wetland Park, Kwazulu-Natal in South Africa. The Comoro Islands specimen was discovered in December 1952. Between 1938 and 1975, 84 specimens were caught and recorded. The second extant species, Indonesian coelacanth, was described from Manado, North Sulawesi, Indonesia in 1999 by Pouyaud et al. based on a specimen discovered by Mark V. Erdmann in 1998 and deposited at the Indonesian Institute of Sciences (LIPI). Erdmann and his wife Arnaz Mehta first encountered a specimen at a local market in September 1997, but took only a few photographs of the first specimen of this species before it was sold. After confirming that it was a unique discovery, Erdmann returned to Sulawesi in November 1997 to interview fishermen to look for further examples. A second specimen was caught by a fisherman in July 1998 and it was then handed to Erdmann.