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-dwelling vertebrates such as amphibians, reptiles, birds, and mammals) than to ray-finned fish. Only one living genus, Latimeria, exists today, and it includes two known species.
The name "coelacanth" comes from the Permian genus Coelacanthus, which was the first scientific name given to coelacanths in 1839. This genus became the type genus for the group Coelacanthiformes as more species were discovered. Fossils of coelacanths have been found in both freshwater and marine deposits dating back to the Devonian period, over 410 million years ago. Scientists once believed they became extinct during the Late Cretaceous period, about 66 million years ago.
The first living coelacanth species, Latimeria chalumnae, was discovered in South African waters starting in 1938. These fish are now also found near the Comoro Islands off Africa’s east coast. A second species, Latimeria menadoensis, was identified in the late 1990s. It lives in the waters of eastern Indonesia, from Manado to Papua.
Coelacanths, or the living genus Latimeria, are often called "living fossils" because they are the only surviving members of a group previously known only from fossils. Their body shape has remained similar to that of ancient coelacanths for about 400 million years. However, fossil studies show that coelacanth body shapes and their roles in ecosystems were much more varied in the past than previously believed, often differing from Latimeria.
Etymology
The word Coelacanth comes from the Modern Latin word 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 parts of the tail fin in the first fossil found and named by Louis Agassiz in 1839, which belonged to the genus Coelacanthus. The genus name Latimeria honors Marjorie Courtenay-Latimer, who discovered the first living specimen of this fish.
Discovery
The first coelacanth fossils were found in the 1800s. Scientists thought these fish had died out at the end of the Cretaceous period. Coelacanths are more closely related to tetrapods than to other types of 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 a fish expert at Rhodes University, J. L. B. Smith. He recognized its importance and sent a message: "Most Important Preserve Skeleton and Gills = Fish Described." This discovery, more than 60 million years after coelacanths were believed to have gone extinct, made them a well-known example of a Lazarus taxon, a group that seemed to disappear from the fossil record but later reappeared. Since 1938, 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 coelacanth from the Comoro Islands was discovered in December 1952. Between 1938 and 1975, 84 coelacanth specimens were caught and recorded.
The second living coelacanth species, the Indonesian coelacanth, was first noticed 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 the discovery was unique, Erdmann returned to Sulawesi in November 1997 to search for more examples. A second specimen was caught in July 1998 and given to Erdmann. The species was officially described in 1999 by Pouyaud and others based on the 1998 specimen, which is stored at the Indonesian Institute of Sciences (LIPI).
During the Paleozoic and Mesozoic eras, coelacanths lived all over the world, except Antarctica. Today, 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 in northern Indonesia, respectively.
Description
Coelacanths are part of a group called Sarcopterygii, which includes lobe-finned fish, lungfish, and tetrapods. All of these animals have lobed fins instead of rayed fins. Coelacanths can be identified 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 divided 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 parts of the coelacanth. Their pectoral fins are large and lobed.
All coelacanths share certain features, such as a strong joint in the skull that may help increase bite force. They also have a special organ called the rostral organ at the front of their head, which detects electrical signals. Coelacanths have two external nostrils, a single bone called the lachrymojugal beneath their eyes, and an upright jaw suspension with a triangular-shaped palate. Their jaws connect at two separate points: one between the quadrate and articular bones, and another between the symplectic and retroarticular bones. The lower jaw has a short, curved dentary bone in living coelacanths, and a large angular bone. 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. The shoulder girdle is not attached to the skull and includes an extracleithrum. The front dorsal fin lacks radial bones and is sail-like in shape. The anal fin and the rear dorsal fin look similar and are shaped like the paired fins. Coelacanth scales are round and overlapping, and they lack ganoine or cosmine. These scales may have denticles, tubercles, or ridges covered in enamel.
Coelacanths also have an oil-filled notochord, a hollow, pressurized tube that is replaced by a vertebral column in most other vertebrates during early development. Fossil coelacanths had a lung surrounded by a heavily calcified casing. In living Latimeria coelacanths, the lung is small and only covered by scattered calcified plates, suggesting it is vestigial and not used for air breathing, unlike in fossil coelacanths, which likely used it for air breathing as seen in early bony fish.
Evolution and taxonomy
Coelacanths are part of a group called Actinistia. Many scientists use the term "coelacanth" to describe all members of Actinistia. The order Coelacanthiformes includes a subgroup of Actinistia, which contains modern coelacanths and other extinct, closely related species that lived from the Permian period onward. Fossils suggest that coelacanths, lungfish, and tetrapods (four-legged animals) split into separate groups during the Silurian period. Over 100 fossil species of coelacanth have been discovered. The oldest known coelacanth fossils are about 420–410 million years old, from the Pragian stage of 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 anatomy. Some scientists also suggest that the slightly older onychodont Styloichthys might be an early coelacanth.
Coelacanths were not as diverse as other fish groups and reached their highest variety during the Early Triassic (252–247 million years ago), a time when many species diversified between the Late Permian and Middle Triassic. Most Mesozoic coelacanths belong to the suborder Latimerioidei, which includes two groups: Latimeriidae, which contains modern coelacanths, and Mawsoniidae, which were found in brackish (a mix of salt and fresh water), freshwater, and marine environments.
Paleozoic coelacanths were generally small, about 30–40 centimeters (12–16 inches) long, while Mesozoic coelacanths were larger. Some Jurassic and Cretaceous mawsoniid coelacanth species, such as Trachymetopon and Mawsonia, may have grown to over 5 meters (16 feet) long, 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, and possibly the earliest Maastrichtian periods in the Eastern and Central 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 undetermined 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 bone analysis methods.
Living coelacanths have been called "living fossils" because they appear similar to older fossil species. However, recent studies suggest that the idea that coelacanths have changed little over time may not be accurate. Fossils show that coelacanths were most diverse in shape and structure during the Devonian and Carboniferous periods, while Mesozoic species were generally similar to each other.
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
After Ferrante and Cavin (2025):
Ecology
Living Latimeria coelacanths are nocturnal fish-eaters that drift around. They often move in a nearly motionless way. These fish eat a variety of prey, including cuttlefish, squid, snipe eels, small sharks, and other fish found in deep reef and volcanic slope habitats. They may swim head down, backward, or belly up to find food. To move, they often use ocean currents by drifting upward or downward. Their paired fins help keep them stable in the water. When on the ocean floor, they do not use these fins for movement. Instead, they use their tail fins to create quick bursts of speed. Their many fins allow them to move in almost any direction. They have been seen swimming upside down or doing headstands. A special organ called the rostral organ helps them sense the electrical signals of prey near their mouths, but not from far away. Thrust for movement mainly comes from their fins. Their paired fins are highly flexible and can move in unusual ways to make precise movements, like a figure-eight pattern.
Fossils show many different body shapes among coelacanths, meaning not all ancient coelacanths lived the same way as modern Latimeria. Some coelacanths, both living and extinct, used suction to catch prey, a trait that evolved early in their history. Fossil evidence from Axelrodichthys, a mawsoniid coelacanth, suggests it swallowed fish whole because its teeth were too small to break them apart. While living Latimeria live in the ocean, some ancient coelacanths, like mawsoniids, lived in brackish or freshwater environments, indicating they may have lived permanently in freshwater or moved between salt and freshwater.
Living Latimeria coelacanths are ovoviviparous, meaning females keep fertilized eggs inside their bodies until they hatch. This process takes about five years. Female Latimeria are usually larger than males, and their scales and skin folds near the cloaca differ. Males lack distinct reproductive organs and have a cloaca with a urogenital papilla surrounded by erectile caruncles. Scientists think the cloaca may turn outward to help during reproduction. The eggs of living coelacanths are large and protected by a thin membrane. Embryos develop inside the mother and are born alive, which is rare for fish. This was discovered in 1975 when scientists found a pregnant coelacanth with five embryos. Baby coelacanths look like adults but have an external yolk sac, larger eyes, and a more sloped body. Their yolk sac hangs below their pelvic fins, and their scales and fins are fully developed, though they lack odontodes, which they gain as they grow.
Female Latimeria give birth to live young, called "pups," in groups of five to 25. The pups can survive on their own immediately after birth. Little is known about their reproductive behaviors, but they likely reach sexual maturity after 20 years. Earlier studies suggested a gestation period of 13 to 15 months, but recent research from 2021 shows it takes 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
Coelacanth fish are not good to eat by humans or other animals that eat fish. Their flesh contains a lot of oil, urea, wax esters, and other substances that make the meat taste very bad, are hard to digest, and can cause stomach problems like diarrhea. The fish also have scales that produce mucus, which, along with the oil in their bodies, makes them feel very slimy. In areas where coelacanths are found, local fishermen avoid catching them because eating them can make people sick. Because of this, coelacanths are not valuable for commercial use except for being displayed in museums or collected by private individuals.
Coelacanths live in deep, remote parts of the ocean, which makes it hard to determine their conservation status. The IUCN currently lists L. chalumnae as "critically endangered," with fewer than 500 individuals remaining. L. menadoensis is classified as "Vulnerable," with a much larger population, though still fewer than 10,000 individuals. The biggest threat to coelacanths is accidental capture by fishing operations, especially from deep-sea trawling.