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Coelacanths ( ) are an ancient group of Sarcopterygii (Sarcopterygii) in the class Actinistia. As sarcopterygians, they are more closely related to lungfish and tetrapods (the terrestrial vertebrates including living , , and ) than to Actinopterygii.
The name coelacanth originates from the Permian genus Coelacanthus, which was the first scientifically named genus of coelacanths (in 1839), becoming the type genus of Coelacanthiformes as other species were discovered and named. Well-represented in freshwater and marine deposits from as early as the Devonian period (more than 410million years ago), they were thought to have become extinct in the Late Cretaceous, around 66million years ago.
The first living species, Latimeria chalumnae, the West Indian Ocean coelacanth, was described from specimens Fishing off the coast of South Africa from 1938 onward; they are now also known to inhabit the seas around the Comoro Islands off the East Africa. The second species, Latimeria menadoensis, the Indonesian coelacanth, was discovered in the late 1990s, which inhabits the seas of Eastern Indonesia, from Manado to Papua.
The coelacanth (more accurately, the extant genus Latimeria) is often considered an example of a "living fossil" in popular science because it was considered the sole remaining member of a taxon otherwise known only from fossils (a biological relict), (1998). 9780412784804, Chapman & Hall. ISBN 9780412784804 evolving a Body plan similar to its current form approximately 400million years ago. However, studies of fossil coelacanths have shown that coelacanth body shapes (and their Ecological niche) were much more diverse than what was previously thought, and often differed significantly from Latimeria.
On 22 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 fisherman. Courtenay-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 over 60 million years after its supposed extinction makes the coelacanth the best-known example of a Lazarus taxon, a taxon or 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, in iSimangaliso Wetland Park, and off the South Coast of 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, the Indonesian coelacanth, was first recognized in Manado, North Sulawesi, Indonesia, by Mark V. Erdmann and his wife Arnaz Mehta at a local fish market in September 1997, but were only able to take 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 and look for further examples. A second specimen was caught by a fisherman in July 1998 and was then handed to Erdmann. The species was described in 1999 by Pouyaud et al. based on Erdmann's 1998 specimen and deposited at a facility of the Indonesian Institute of Sciences (LIPI).
Some species of Actinistians, especially the Mawsoniidae, were found in deposits corresponding to Brackish water and even freshwater environments, suggesting an anadromous ability.
The two extant Latimeria species, the West Indian Ocean coelacanth and the Indonesian coelacanth, are restricted to a few locales within the Indo-Pacific and are named base on their range.
The soft tissue of coelacanths is mostly known from Latimeria, the relictual extant genus.
Coelacanths were never a Biodiversity in comparison to other groups of fish, and reached a peak diversity during the Early Triassic (252–247 million years ago), coinciding with a burst of diversification between the Late Permian and Middle Triassic. Most Mesozoic coelacanths belong to the suborder Latimerioidei, which contains two major subdivisions, the marine Latimeriidae, which contains modern coelacanths, as well as the extinct Mawsoniidae, which were native to Brackish water, freshwater as well as marine environments.
Paleozoic coelacanths are generally small (~ in length), while Mesozoic forms were larger. Several specimens belonging to the Jurassic and Cretaceous mawsoniid coelacanth genera Trachymetopon and Mawsonia likely reached or exceeded in length, making them amongst the largest known fishes of the Mesozoic, and amongst the largest bony fishes of all time.
The most recent fossil latimeriid is Megalocoelacanthus dobiei, whose disarticulated remains are found in late Santonian to middle Campanian, and possibly earliest Maastrichtian-aged marine strata of the Eastern and Central United States, the most recent mawsoniids are Axelrodichthys from early Campanian to early Maastrichtian freshwater continental deposits of France, as well as an indeterminate marine mawsoniid from Morocco, dating to the late Maastrichtian A small bone fragment from the Paleocene has been considered the only plausible post-Cretaceous record, but this identification is based on comparative bone histology methods of doubtful reliability.
Living coelacanths have been considered "" based on their supposedly conservative morphology relative to fossil species; however, recent studies have expressed the view that coelacanth morphologic conservatism is a belief not based on data. Fossils suggest that coelacanths were most morphologically diverse during the Devonian and Carboniferous, while Mesozoic species are generally morphologically similar to each other.
Cladogram showing the relationships of coelacanth genera after Torino, Soto and Perea, 2021.
After Ferrante and Cavin (2025):
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