The coelacanth (more accurately, the extant genusLatimeria) is often considered an example of a "living fossil" inpopular science because it was considered the sole remaining member of ataxon otherwise known only from fossils (abiological relict),[9][10]: 1 evolving abodyplan similar to its current form approximately 400million years ago.[1] However, studies of fossil coelacanths have shown that coelacanth body shapes (and theirniches) were much more diverse than what was previously thought, and often differed significantly fromLatimeria.[11][12][13]
The wordCoelacanth is an adaptation of the Modern LatinCœlacanthus ('hollow spine'), from theAncient Greekκοῖλ-ος (koilos, 'hollow') andἄκανθ-α (akantha, 'spine'),[14] referring to the hollowcaudal fin rays of the first fossil specimen described and named byLouis Agassiz in 1839, belonging to the genusCoelacanthus.[10]: 1 The genus nameLatimeria commemoratesMarjorie Courtenay-Latimer, who discovered the first specimen.[15]
The earliest fossils of coelacanths were discovered in the 19th century. Coelacanths were believed to have becomeextinct at the end of theCretaceous period.[16] More closely related to tetrapods than to theray-finned fish, coelacanths were considered atransitional form between fish and tetrapods.[17]
On 22 December 1938, the firstLatimeria specimen was found off the east coast of South Africa, off theChalumna River (now Tyolomnqa).[6][18][19] Museum curatorMarjorie Courtenay-Latimer discovered the fish among the catch of a local fisherman.[6] 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."[6] Its discovery over 60 million years after its supposed extinction makes the coelacanth the best-known example of aLazarus 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 theComoros,Kenya,Tanzania,Mozambique,Madagascar, iniSimangaliso Wetland Park, and off the South Coast ofKwazulu-Natal in South Africa.[20][21]
TheComoro Islands specimen was discovered in December 1952.[22] Between 1938 and 1975, 84 specimens were caught and recorded.[23]
The secondextant species, theIndonesian coelacanth, was first recognized inManado, North Sulawesi, Indonesia, by Mark V. Erdmann and his wife Arnaz Mehta at a localfish 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.[24][25] The species wasdescribed in 1999 by Pouyaud et al.[26] based on Erdmann's 1998 specimen[27] and deposited at a facility of theIndonesian Institute of Sciences (LIPI).[28]
This sectionis missing information about the countries and continents that fossil coelacanths were found in. Please expand the section to include this information. Further details may exist on thetalk page.(September 2025)
The two extantLatimeria species, the West Indian Ocean coelacanth and the Indonesian coelacanth, are restricted to a few locales within theIndo-Pacific and are named base on their range.[39]
Coelacanths are a part ofSarcopterygii or the lobe-finned fishes, the sameclade as the lungfish andtetrapods, and they all possess lobed fins as opposed to rayed fins. Externally, severalcharacteristics distinguish coelacanths from other lobe-finned fish: coelacanths have eightfins – two dorsal fins, two pectoral fins, two pelvic fins, one anal fin and one caudal fin. The tail is very nearly equally proportioned and is split by a terminal tuft of fin rays that make up its caudal lobe; this is alternatively termed a trilobate fin (three-lobed) or a diphycercal tail. A secondary tail extending past the primary tail separates the upper and lower halves of the coelacanth.[clarification needed] Ctenoid elasmoid scales act as thick armor to protect the coelacanth's exterior. Several internal traits also aid in differentiating coelacanths from other lobe-finned fish. At the back of the skull, the coelacanth possesses a hinge, theintracranial joint, which allows it to open its mouth extremely wide. Coelacanths also retain an oil-fillednotochord, a hollow, pressurized tube which is replaced by avertebral column early in embryonic development in most other vertebrates.[40][better source needed] The body is covered inctenoidelasmoid scales that act as armor.[41]
The soft tissue of coelacanths is mostly known fromLatimeria, therelictual extant genus.
Specimen ofLibys (Latimeriidae) from the Upper Jurassic of GermanyEstimated size of the largest known individual of the Jurassic-Cretaceous freshwater coelacanthMawsonia compared to a humanLife restoration of the basal coelacanthAllenypterus from the Carboniferous of North America
Coelacanths are members of the class Actinistia, with many researchers considering the term "coelacanth" to cover all members of Actinistia.[42][43] The order Coelacanthiformes has been used for a subgroup of actinistians, containing the modern coelacanths, as well as other extinct closely related actinistians spanning from thePermian onwards.[44][45] According to the fossil record, the divergence of coelacanths,lungfish, andtetrapods is thought to have occurred during theSilurian.[46] Over 100 fossil species of coelacanth have been described.[42] The oldest identified coelacanth fossils are around 420–410 million years old, dating to thePragian stage of the earlyDevonian. These includeEoactinistia from Australia, known only from a fragmentary jaw, as well asEuporosteus yunnanensis from China, known from a partial skull that indicates it to be the earliest anatomically modern coelacanth.[1][43] Some authors have also suggested that the slightly olderonychodontStyloichthys may also be an early coelacanth.[47]
Coelacanths were never adiverse group in comparison to other groups of fish, and reached a peak diversity during theEarly Triassic (252–247 million years ago),[29] coinciding with a burst of diversification between the Late Permian and Middle Triassic.[42] MostMesozoic coelacanths belong to the suborder Latimerioidei, which contains two major subdivisions, the marineLatimeriidae, which contains modern coelacanths, as well as the extinctMawsoniidae, which were native tobrackish, freshwater as well as marine environments.[48]
Paleozoic coelacanths are generally small (~30–40 cm or 12–16 in in length), while Mesozoic forms were larger.[42] Several specimens belonging to the Jurassic and Cretaceous mawsoniid coelacanth generaTrachymetopon andMawsonia likely reached or exceeded 5 metres (16 feet) in length, making them amongst the largest known fishes of the Mesozoic, and amongst thelargest bony fishes of all time.[49]
The most recent fossil latimeriid isMegalocoelacanthus dobiei, whose disarticulated remains are found in lateSantonian to middleCampanian, and possibly earliestMaastrichtian-aged marine strata of the Eastern and Central United States,[50][51][52] the most recent mawsoniids areAxelrodichthys megadromos from early Campanian to early Maastrichtian freshwater continental deposits of France,[53][30][29] as well as an indeterminate marine mawsoniid from Morocco, dating to the late Maastrichtian[54] A small bone fragment from theEuropeanPaleocene has been considered the only plausible post-Cretaceous record, but this identification is based on comparative bone histology methods of doubtful reliability.[50][55]
Living coelacanths have been considered "living fossils" based on their supposedly conservativemorphology relative to fossil species;[39][10]: 1 however, recent studies have expressed the view that coelacanth morphologic conservatism is a belief not based on data.[11][12][13][56] Fossils suggest that coelacanths were most morphologically diverse during the Devonian and Carboniferous, while Mesozoic species are generally morphologically similar to each other.[42]
Cladogram showing the relationships of coelacanth genera after Torino, Soto and Perea, 2021.[42]
^abcForey, Peter L (1998).History of the Coelacanth Fishes. London: Chapman & Hall. pp. 1, 3, 6,13–16, 19, 27, 32,35–40.ISBN978-0-412-78480-4.
^abFriedman, Matt; Coates, Michael I.; Anderson, Philip (2007). "First discovery of a primitive coelacanth fin fills a major gap in the evolution of lobed fins and limbs".Evolution & Development.9 (4):329–37.doi:10.1111/j.1525-142X.2007.00169.x.PMID17651357.S2CID23069133.
^abWendruff, Andrew J.; Wilson, Mark V. H. (2012). "A fork-tailed coelacanth, Rebellatrix divaricerca, gen. Et sp. Nov. (Actinistia, Rebellatricidae, fam. Nov.), from the Lower Triassic of Western Canada".Journal of Vertebrate Paleontology.32 (3):499–511.Bibcode:2012JVPal..32..499W.doi:10.1080/02724634.2012.657317.S2CID85826893.
^Venter, P.; Timm, P.; Gunn, G.; le Roux, E.; Serfontein, C. (2000). "Discovery of a viable population of coelacanths (Latimeria chalumnae Smith, 1939) at Sodwana Bay, South Africa".South African Journal of Science.96 (11/12):567–568.
^Gee, Henry (1 October 1998). "Coelacanth discovery in Indonesia".Nature.doi:10.1038/news981001-1.
^"The Discovery". University of California Museum of Paleontology.
^Pouyaud, Laurent; Wirjoatmodjo, Soetikno; Rachmatika, Ike; Tjakrawidjaja, Agus; Hadiaty, Renny; Hadie, Wartono (1999). "Une nouvelle espèce de cœlacanthe. Preuves génétiques et morphologiques" [A new species of coelacanth. Genetic and morphologic proof].Comptes Rendus de l'Académie des Sciences (in French).322 (4):261–7.Bibcode:1999CRASG.322..261P.doi:10.1016/S0764-4469(99)80061-4.PMID10216801.
^González-Rodríguez, K.A.; Fielitz, Ch.; Bravo-Cuevas, V.M.; Baños-Rodríguez, R.E. (2016). "Cretaceous osteichthyan fish assemblages from Mexico".New Mexico Museum of Natural History and Science Bulletin.71:107–119.
^Sherman, Vincent R. (2016). "A comparative study of piscine defense: The scales ofArapaima gigas,Latimeria chalumnae andAtractosteus spatula".Journal of the Mechanical Behavior of Biomedical Materials.73:1–16.doi:10.1016/j.jmbbm.2016.10.001.PMID27816416.
^Cavin, Lionel; Cupello, Camila; Yabumoto, Yoshitaka; Léo, Fragoso; Deersi, Uthumporn; Brito, Paul M. (2019)."Phylogeny and evolutionary history of mawsoniid coelacanths"(PDF).Bulletin of the Kitakyushu Museum of Natural History and Human History, Series A.17:3–13.
^Ørvig, Tor (1 June 1986). "A vertebrate bone from the Swedish Paleocene".Geologiska Föreningen i Stockholm Förhandlingar.108 (2):139–141.doi:10.1080/11035898609452636.ISSN0016-786X.
Butler, Carolyn (August 2012)."Der Quastenflosser: Ein Fossil taucht auf" [The Coelacanth: A fossil turns up].National Geographic Deutschland (in German). Archived fromthe original on 3 February 2017. Retrieved19 April 2013.
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