Coelacanths are an ancient group of lobe-finned fish in the class Actinistia. As sarcopterygians, they are more closely related to lungfish and tetrapods (land animals such as amphibians, reptiles, birds, and mammals) than to ray-finned fish. Only one living genus, Latimeria, exists today, with two known species.
The name "coelacanth" comes from the Permian genus Coelacanthus, which was the first scientifically named group of coelacanths in 1839. This genus became the type group for Coelacanthiformes as more species were discovered. Fossils of coelacanths are found in both freshwater and marine deposits dating back to the Devonian period (over 410 million years ago). Scientists once believed they went extinct during the Late Cretaceous period, about 66 million years ago.
The first living coelacanth species, Latimeria chalumnae, was discovered in South Africa starting in 1938. These fish now also live near the Comoro Islands off Africa’s east coast. A second species, Latimeria menadoensis, was found in the late 1990s in Eastern Indonesia, near Manado and Papua.
Coelacanths (or the living genus Latimeria) are often called "living fossils" in popular science because they were once thought to be the only surviving member of a group known only from fossils. Their body shape has remained similar to its form from about 400 million years ago. However, fossil studies show that ancient coelacanths had more varied body shapes and filled different ecological roles than modern Latimeria.
Etymology
The word Coelacanth comes from the Modern Latin Cœlacanthus, which means "hollow spine." This name is based on the Ancient Greek words κοῖλ-ος (koilos, meaning "hollow") and ἄκανθ-α (akantha, meaning "spine"). It refers to the hollow tail fin rays of the first fossil discovered and named by Louis Agassiz in 1839. This fossil belongs to the genus Coelacanthus. The genus name Latimeria honors Marjorie Courtenay-Latimer, who found the first living specimen of this fish.
Discovery
The first coelacanth fossils were found in the 1800s. Scientists thought these fish had gone extinct at the end of the Cretaceous period. Coelacanths are more closely related to tetrapods than to ray-finned fish, making them a link between fish and tetrapods.
On December 22, 1938, the first Latimeria specimen was discovered near the Chalumna River (now Tyolomnqa) off the east coast of South Africa. A museum curator named Marjorie Courtenay-Latimer found the fish in a local fisherman’s catch. She sent drawings of the fish to J. L. B. Smith, a fish expert at Rhodes University. Smith confirmed its importance with a message: "Most Important Preserve Skeleton and Gills = Fish Described." This discovery, over 60 million years after coelacanths were thought to have disappeared, made them a well-known example of a Lazarus taxon—a group that seemed to vanish from the fossil record but later reappeared. Since 1938, West Indian Ocean coelacanths have been found in the Comoros, Kenya, Tanzania, Mozambique, Madagascar, iSimangaliso Wetland Park, and along the South Coast of KwaZulu-Natal in South Africa.
A specimen from the Comoro Islands was found in December 1952. Between 1938 and 1975, 84 coelacanth specimens were caught and recorded.
The second living coelacanth species, the Indonesian coelacanth, was first identified in September 1997 in Manado, North Sulawesi, Indonesia, by Mark V. Erdmann and his wife, Arnaz Mehta, at a local fish market. They took photos of the first specimen before it was sold. After confirming its uniqueness, Erdmann returned to Sulawesi in November 1997 to speak with fishermen and search for more examples. A second specimen was caught in July 1998 and given to Erdmann. Scientists described the species in 1999 using the 1998 specimen, which is stored at the Indonesian Institute of Sciences (LIPI).
During the Paleozoic and Mesozoic eras, coelacanths lived worldwide, with remains found on every continent except Antarctica. The two living Latimeria species, the West Indian Ocean coelacanth and the Indonesian coelacanth, are found only along the southern and eastern coasts of Africa and northern Indonesia, respectively.
Description
Coelacanths belong to a group called Sarcopterygii, which includes lobe-finned fish, such as lungfish and tetrapods. These fish have lobed fins, not rayed fins. Coelacanths can be distinguished from other lobe-finned fish by their eight fins: two dorsal fins, two pectoral fins, two pelvic fins, one anal fin, and one caudal fin. Their tail is nearly equal in size on both sides and is split by a tuft of fin rays, forming a three-lobed or trilobate tail. A secondary tail extends beyond the main tail, separating the upper and lower halves of the coelacanth. Their pectoral fins are lobed and longer than other fins.
All coelacanths share several traits. They have a strong joint in the skull that may help increase bite force. A special organ called the rostral organ, used for sensing electric fields, is located at the front of the head. They have two external nostrils, a single bone called the lachrymojugal beneath the eyes, and an upright jaw structure with a triangular-shaped palate. The lower jaw has two separate points of connection: one between the quadrate and articular bones, and another between the symplectic and retroarticular bones. The dentary bone on the lower jaw is short and curved in living coelacanths, while the angular bone is large. The maxilla, a main tooth-bearing bone in other fish, is missing in coelacanths, along with other bones like the submandibulars, branchiostegals, and the jugal in some species. Their shoulder girdle is not attached to the skull and includes an extracleithrum. The front dorsal fin lacks radial bones and is shaped like a sail. The anal fin and the rear dorsal fin are similar in shape to the paired fins. Their scales are round and overlapping, without ganoine or cosmine, and may have denticles, tubercles, or enamel-covered ridges.
Coelacanths also have an oil-filled notochord, a hollow, pressurized tube that is replaced by a backbone in most other vertebrates during early development. Fossil coelacanths had a lung surrounded by a heavily calcified casing, but living coelacanths have a small, vestigial lung with only scattered calcified plates. This lung is not large or functional, unlike in fossil coelacanths, which likely used it for breathing air and hearing.
Evolution and taxonomy
Coelacanths are part of the class Actinistia. Many scientists use the term "coelacanth" to describe all members of this class. The order Coelacanthiformes includes a group of actinistians that contains modern coelacanths and other closely related, now-extinct species that lived from the Permian period onward. Fossil evidence suggests that coelacanths, lungfish, and tetrapods split into separate groups during the Silurian period. Over 100 different fossil species of coelacanth have been discovered. The oldest known coelacanth fossils are about 420 to 410 million years old, from the early Devonian period. These include Eoactinistia from Australia, known only from a jaw fragment, and Euporosteus yunnanensis from China, known from a partial skull that shows it was one of the earliest coelacanths with modern features. Some scientists also think the slightly older onychodont Styloichthys might be an early coelacanth.
Coelacanths were not as diverse as other groups of fish. Their greatest diversity occurred during the Early Triassic period (252 to 247 million years ago), which followed a period of rapid diversification between the Late Permian and Middle Triassic. Most coelacanths from the Mesozoic era belong to the suborder Latimerioidei, which includes two main groups: the marine Latimeriidae, which contains modern coelacanths, and the extinct Mawsoniidae, which lived in brackish, freshwater, and marine environments.
Paleozoic coelacanths were generally small, about 30 to 40 centimeters (12 to 16 inches) long, while Mesozoic coelacanths were larger. Some Jurassic and Cretaceous mawsoniid coelacanths, such as Trachymetopon and Mawsonia, may have grown to over 5 meters (16 feet) in length, making them among the largest known fish of the Mesozoic and among the largest bony fish in history.
The most recent fossil latimeriid is Megalocoelacanthus dobiei, found in marine rock layers from the late Santonian to middle Campanian periods, and possibly the earliest Maastrichtian period, in the United States. The most recent mawsoniids include Axelrodichthys megadromos, found in freshwater deposits in France from the early Campanian to early Maastrichtian periods, and an unknown mawsoniid from Morocco dating to the late Maastrichtian. A small bone fragment from the European Paleocene is the only possible record of coelacanths after the Cretaceous period, but this identification is based on uncertain methods.
Living coelacanths are sometimes called "living fossils" because their physical features seem similar to ancient species. However, recent studies suggest that their physical similarity to fossils may not be supported by strong evidence. Fossils show that coelacanths were most diverse in shape during the Devonian and Carboniferous periods, while Mesozoic coelacanths were generally similar in appearance.
Cladogram showing the relationships of coelacanth genera after Torino, Soto, and Perea, 2021.
† Mimipiscis (Actinopterygii)
† Porolepis († Porolepiformes)
† Guizhoucoelacanthus
† Luopingcoelacanthus
After Ferrante and Cavin (2025):
† Guizhoucoelacanthus
Ecology
Living Latimeria coelacanths are nocturnal fish that hunt other fish by drifting nearly motionless in the water. They are opportunistic feeders, eating cuttlefish, squid, snipe eels, small sharks, and other fish found in deep reef and volcanic slope habitats. To find prey, Latimeria swim head down, backward, or belly up. They often use ocean currents to move around, relying on their paired fins to stay stable in the water. On the ocean floor, they do not use their paired fins for movement. Instead, they use their caudal fins to create quick bursts of speed. Their many fins allow them to move in nearly any direction in the water. Latimeria have been observed swimming upside down or in headstands. The rostral organ, a special structure on their head, helps them sense prey near their mouths just before striking, rather than detecting prey from a distance. Thrust for movement is mainly created by their fins, which are highly mobile and can move in unusual ways to perform precise motions, such as a figure-eight pattern.
Fossil coelacanth remains show a variety of body shapes, suggesting that not all ancient coelacanths lived like modern Latimeria. Scientists believe that both living and extinct coelacanths used suction to capture prey, a trait that evolved early in their history, by the end of the Devonian period. Fossil evidence from Axelrodichthys, a mawsoniid coelacanth found in Brazil, shows it ate fish whole, as its small teeth could not break prey apart. While modern Latimeria live in marine environments, some ancient coelacanths, like mawsoniids, lived in brackish or freshwater areas, indicating they may have lived permanently in freshwater or moved between saltwater and freshwater.
Living Latimeria coelacanths are ovoviviparous, meaning females keep fertilized eggs inside their bodies until the embryos develop for about five years. Female Latimeria are typically larger than males, with differences in scales and skin folds near the cloaca. Males lack distinct copulatory organs and instead use their cloaca, which has a urogenital papilla surrounded by erectile caruncles. Scientists think the cloaca may evert to act as a copulatory organ. Latimeria eggs have a thin protective membrane and hatch inside the mother, who gives birth to live young called "pups" in groups of five to 25. The pups are born fully capable of surviving on their own. This reproductive method was discovered in 1975 when the American Museum of Natural History found five embryos inside a coelacanth. Young coelacanths resemble adults but have an external yolk sac, larger eyes, and a more pronounced downward body slope. Juveniles have fully developed scales and fins but lack odontodes, which they gain as they mature.
Female Latimeria give birth to live young in groups of five to 25 pups. Their reproductive behaviors are not well understood, but they likely reach sexual maturity after 20 years. Earlier studies suggested a gestation period of 13 to 15 months, but research from 2021 found the gestation period to be up to five years, which is 1.5 years longer than the gestation time of the deep-sea frilled shark, the previous record holder.
Relation to humans
Living coelacanths are not a good food source for humans or other fish-eating animals. Their flesh contains large amounts of oil, urea, wax esters, and other substances that make it taste bad, hard to digest, and may cause diarrhea. The scales of coelacanths secrete mucus. This, along with the oil their bodies produce, makes them very slimy when eaten. In areas where coelacanths are more common, local fishermen avoid catching them because eating them can make people sick. As a result, living coelacanths have no real commercial value except for being highly valued by museums and private collectors.
Because coelacanths live in remote deep-sea areas, it is hard to determine their conservation status. The IUCN currently classifies L. chalumnae as "critically endangered" and L. menadoensis as "Vulnerable." The main threat to coelacanths is accidental capture by fishing operations, especially commercial deep-sea trawling.