The Coelacanth – A Remarkable Survivor but now under Threat

Coelacanth fossils have been found in rock strata dating from the Mid Devonian (approximately 370 million years ago) to sedimentary rock laid down at the end of the Cretaceous (65 million years ago). Scientists had thought that this once diverse and widespread group of fishes died out with the dinosaurs. However, the discovery of a living Coelacanth specimen in late December 1938 changed our view.

In what became known as the “scientific sensation of the age”, and much to the surprise of palaeontologists, it was soon to become clear that representatives of the Coelacanthiformes Order had survived to the present day. In fact, we know that there are at least two species living today. Unfortunately, as a result of over fishing, specimen hunting and the destruction of the Coelacanth’s unique habitat at least one of the species known to science is now in danger of extinction.

The fossil record of Coelacanths shows that these Sarcopterygians (lobe-finned or fleshy finned fishes) were a highly successful and diverse group of fishes throughout the Palaeozoic and the Mesozoic. Although, the two extant (still living today, as opposed to extinct), species are entirely marine, fossils of Coelacanths have been found associated with ancient river systems and lakes indicating that some of this widespread group of fishes lived in freshwater environments as well as marine habitats.

The term Coelacanth means “Hollow Spines” a reference to the arrangement of hollow spines to be found in the fins. However, it is the distinctive, fleshy paired fins that are characteristic of this particular member of the Sarcopterygii. The fins have large bones and muscle attachments at their base, and it was once thought by scientists that these creatures used their fleshy fins to “walk” on the seabed, an adaptation that would lead these creatures to venture out of the water and live on land.

Recent fossil finds, have disproved this theory, the Coelacanth is not now regarded as a direct ancestor of the first land living Tetrapods. Ironically, seabed “walking” has not been observed by marine biologists studying the extant Coelacanths in their natural habitat. These animals are slow swimmers, but do not as far as we know, use their fins as modified limbs to clamber around their rocky reef environments, where they can be found. They are capable of moving the fins independently and they are used to help keep the animal stable and for steering in the water column but the main propulsion comes from the strong muscular three-lobed tail.

Modern Coelacanths – The Living Fossil Myth

A fishing vessel, trawling off the coast of South Africa in December 1938, hauled aboard a strange looking fish. On returning to port, Marjorie Courtney-Latimer, the curator of the nearby East London museum was notified and it was her notes and illustration of the bizarre 1.5 metre long specimen that led to this creature being identified as a Coelacanth. The discovery caused a sensation in scientific circles and the South African fish expert JLB Smith and his colleagues set about interviewing local fishermen to see if a second specimen could be captured.

The discovery of a living Coelacanth was heralded as the “biological discovery of the age”, but it is not particularly accurate to call Coelacanths “living fossils”. The extant genus, Latimeria (named after the curator of the East London museum), does resemble extinct forms but it is highly unlikely that it has remained unchanged since the Palaeozoic. Latimeria may belong to the same family of Coelacanths such as the genus Macropoma, a particular type of marine Coelacanth that became extinct around 70 million years ago. It is more appropriate to suggest that the Latimeria are living representatives of an extremely old Order of fish.

The Threat to Coelacanths Today

There are two species of Coelacanth known, the first species to be named was the East African species Latimeria chalumnae an example of which was sensationally discovered in 1938. A second specimen was not found until 1952, the retrieval of this fish from the Comoro Island (a small island of Madagascar), where it had been caught; caused a diplomatic row between France and South Africa. The South African fish expert, JLB Smith had been given permission by the South African Government to fetch the specimen back to South Africa and was provided with a military plane to make the journey. Unfortunately, the Comoro Islands were controlled by France and the French Government objected most strongly to the intervention of a South African scientist and the use of French airspace by a military plane.

A second species of Coelacanth was identified in 1998, it lives in the deep waters of the islands of Indonesia. Despite being known to science for over 70 years, we still know very little about these deep water fish. They inhabit sea caves and rocky reefs and live in waters ranging in depth from 150 metres to 700 metres deep. The females tend to be larger than the males and some individuals can grow up to 1.7 metres long and weigh as much as ninety kilogrammes. Ironically, the extant Coelacanths are much bigger than their ancient, extinct relatives. Fossils of the genus Macropoma, for example, rarely exceed 60 centimetres in length.

Little is known about the breeding habits and general behaviour of Coelacanths, although they have been observed and filmed in their natural environment. Any Coelacanth that is caught in a fisherman’s net and hauled to the surface is most likely to die. These fish have an extremely inefficient set of gills and only absorb oxygen slowly, the effort, stress and rapid change in water pressure as they are dragged to the surface of the sea is usually enough to kill them or leave them mortally wounded. Scientists do know that these fish are ovoviparous (fish that produce eggs but keep them inside the female’s body until hatching occurs). Juveniles still attached to a large yolk sac that they were born with have been filmed by marine scientists. As many as twenty-five young may be born at any one time.

Coelacanths are nocturnal hunters, the extant species have large eyes and a hinged mouth that enables them to suck in small prey items such as fish, crabs and squid that are hiding away in rock crevices. About a dozen of so Coelacanths are caught each year, and the catch, once despised by local fisherman as the fish tastes foul, is prized by scientists and private collectors who pay large sums for their own study specimen. The overfishing of waters in the Indian Ocean, coupled with the loss of habitat and pollution as new, deep water ports are developed on the coast of East Africa has led to marine biologists becoming concerned over the plight of the Coelacanth.

The World Conservation Union (IUCN) lists one species of Coelacanth as “Critically Endangered” meaning that if faces an extremely high risk of extinction in the wild in the near future. Less than seventy-five years since the “biological discovery of the age”, the Coelacanth may be facing extinction.

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