Science · Biology

Coelacanth

Rediscovered alive, 22 December 1938

Biology — lobe-finned fishes, a Lazarus taxon

Coelacanths are lobe-finned fishes known from fossils going back some 400 million years and assumed to have died out with the dinosaurs — until a living one was hauled up off the South African coast just before Christmas 1938. Marjorie Courtenay-Latimer, curator of the East London Museum, rescued the strange blue fish from a trawler's catch, and the ichthyologist J. L. B. Smith identified it and named it Latimeria chalumnae in her honour. A second living species, Latimeria menadoensis, turned up in an Indonesian market in 1997. They are deep-water, cave-dwelling fish with fleshy, limb-like fins, a hinge across the skull that lets the snout swing up, an electrosensory rostral organ, a fat-filled vestigial lung, and live-born young after a gestation of about five years. As the nearest living fish relatives of the tetrapods, along with the lungfishes, they occupy a celebrated place near the ancestry of all four-limbed animals.

How to spot them

▸Known only as a fossil until a living one was landed off South Africa in December 1938
▸Named for Marjorie Courtenay-Latimer, who spotted it in a trawler's catch
▸Fleshy, limb-like lobed fins and a hinged skull that lets the snout swing upwards
▸The classic Lazarus taxon, thought extinct for some 66 million years
▸With the lungfishes, the closest living fish relative of the four-limbed vertebrates

Key facts

Marjorie Courtenay-Latimer pulled it, blue and strange, from a trawler's catch at East London in December 1938 (1938)

She sketched it and wrote to J. L. B. Smith, who replied with the famous telegram urging her to preserve the skeleton and gills

J. L. B. Smith named the genus in 1939 after the museum curator who found it (1939)

Latimeria chalumnae — the species name from the Chalumna River, off whose mouth it was trawled

A fourteen-year hunt with reward posters ended with a second specimen in the Comoros in 1952 (1952)

Smith flew there in a South African military aircraft lent by prime minister D. F. Malan

A second living species was spotted on a market stall in Manado, Sulawesi, in 1997 (1997)

Noticed by Mark Erdmann; described as Latimeria menadoensis in 1999

Its name means 'hollow spine', from the hollow tube that serves as its backbone

Greek koilos and akantha; the notochord persists through life as an oil-filled tube

Scale growth rings showed in 2021 that it lives to about a century, gestating young for five years (2021)

Its maximum age had been underestimated fivefold; females reach maturity around 55

Smith's 1956 book about the search for it was called Old Fourlegs (1956)

A bestseller that made the fish a household name

Key ideas

A 'Lazarus taxon' is a group that disappears from the fossil record and later reappears — here across some 66 million years. The gap does not mean the lineage vanished, only that it left no fossils, and the living fish are not identical to their Cretaceous relatives.
The intracranial joint, a hinge running right across the braincase, lets the front of the skull swing upwards so the mouth gapes wide — a feature no other living vertebrate possesses.

Quick-fire facts

•Two living species: Latimeria chalumnae (Smith, 1939) off eastern Africa and the Comoros, and Latimeria menadoensis (Pouyaud et al., 1999) off Sulawesi
•Subclass Sarcopterygii, the lobe-finned fishes; order Coelacanthiformes
•The name comes from Louis Agassiz's fossil genus Coelacanthus, 'hollow spine', named in 1839
•Adults reach about 2 m and 90 kg; they are deep blue-grey with white flecks, individually distinctive
•They live at roughly 100–500 m, resting by day in submarine lava caves and hunting at night, drifting head-down
•They are ovoviviparous, giving birth to live young; a 1975 dissection at the American Museum of Natural History found 26 developing pups
•The rostral organ in the snout is a jelly-filled electroreceptor used to detect prey
•The swim bladder is a fat-filled vestigial lung, evidence of a shared ancestry with air-breathing vertebrates
•The African species genome was published in Nature in 2013; it evolves unusually slowly, and confirmed the lungfishes as the tetrapods' closest living relatives
•Common misconception: it is not the ancestor of land vertebrates, nor did it 'walk' onto land — it is a deep-sea cousin on a neighbouring branch, and it has not stayed unchanged since the Devonian

Drill it — 10 cards

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Sources

Chris T. Amemiya et al., Nature 496 (2013) — The African coelacanth genome provides insights into tetrapod evolution
Kélig Mahé et al., Current Biology 31 (2021) — New scale analyses reveal centenarian African coelacanths Annual circuli on scales; lifespan about a century, gestation about five years
J. L. B. Smith — Old Fourlegs: The Story of the Coelacanth