Why Is the Coelacanth Called a Living Fossil? (And Is It?)

The coelacanth is called a "living fossil" because scientists knew coelacanths only from fossils, and believed the group had died out in the Late Cretaceous roughly 66–70 million years ago, until a living one was landed off South Africa in December 1938. The living fish also shares many anatomical features with its fossil relatives, and it is the last branch of a lineage that goes back more than 410 million years and includes more than 175 described fossil taxa. Two species survive: the West Indian Ocean coelacanth (Latimeria chalumnae) and the Indonesian coelacanth (Latimeria menadoensis).

The label is shorthand, and biologists debate it. The fish caught in 1938 belonged to a species new to science, not to a species known from rocks, and studies of coelacanth fossils and of the living fish's genome show that the lineage kept changing: more slowly in some respects than most vertebrates, but not frozen.

What happened in 1938?

In late December 1938 the trawler Nerine, skippered by Hendrick Goosen, returned to East London, South Africa, after fishing off the mouth of the Chalumna River. Marjorie Courtenay-Latimer, the 32-year-old curator of the town's small museum, had an arrangement to look through the skipper's catch for unusual specimens. Among it was a fish over 1 m (3.3 ft) long, bluish, with fleshy fins that resembled the limbs of land vertebrates. She compared it with pictures of prehistoric fish in her reference books, made a rough sketch and mailed it to Rhodes University in Grahamstown.

By the time a reply came, the fish had been mounted and its internal organs thrown away. Professor J. L. B. Smith of Rhodes University reached the museum on 16 February 1939 and identified the fish as a coelacanth. He named it Latimeria chalumnae, after Courtenay-Latimer and the Chalumna River.

The identification was startling because coelacanths were then known only from fossils. A living specimen did not bring a fossil species back to life; it showed that one branch of the lineage had survived in deep water without being noticed by science. It was almost 15 years before a second specimen was found, in the Comoros in 1952.

Preserved holotype specimen of the West Indian Ocean coelacanth

The 1938 specimen became the holotype used to define Latimeria chalumnae. Photo by Bernard DUPONT via Wikimedia Commons, CC BY-SA 2.0.

Why does the label fit?

There is no single test for a living fossil. A 2023 study of how the term has been used since 1860 lists the criteria biologists apply, among them a long geological duration, similarity to ancestors, having far fewer species today than in the past, having been known as a fossil before being found alive, and a slow rate of evolution. Living fossil status is almost always granted by comparison with similar organisms. The coelacanth meets several criteria at once:

Known as a fossil first. The group was known only from fossils before 1938.
Long duration. The earliest coelacanth fossils come from the Lower Devonian, about 419–411 million years ago.
Far fewer species today. More than 175 fossil coelacanth taxa have been described, and their diversity peaked in the Triassic. Two species live today.
Similarity to ancestors. A 2024 analysis of all coelacanths found that, in discrete anatomical characters, Latimeria has moved little outside the range of its closest Mesozoic relatives, despite an additional 66 million years to evolve.
Slow molecular change. The 2013 genome study found that coelacanth protein-coding genes have changed at about half the rate of tetrapod genes since the two lineages split.

The 1938 fish was recognizable as a coelacanth because its overall form matched fossil coelacanths. Living coelacanths also have features unusual among living fish: seven fins on fleshy lobes, with the paired fins moving in a diagonal pattern like the legs of a four-legged animal; a fluid-filled notochord in place of bony vertebrae; and an intracranial joint, a joint inside the skull that no other living vertebrate has.

Fossil of the extinct coelacanth relative Allenypterus montanus

The Carboniferous Allenypterus montanus was an unusually shaped coelacanth, one of many forms the group once included. Photo by Bloopityboop via Wikimedia Commons, CC BY-SA 4.0.

Why do biologists debate it?

The phrase "living fossils" appears in Charles Darwin's On the Origin of Species (1859), where he applied it to the platypus, a lungfish and the ganoid fishes. Since then it has been applied to hundreds of organisms for many different reasons, and no single definition covers every use. Critics see the concept as too open-ended; the authors of the 2023 study argue for keeping it as a broad umbrella term. A 2013 review titled "Why coelacanths are not 'living fossils'" argued that fossil evidence does not support the idea that coelacanth anatomy stood still, and that terms such as "living fossil" make no sense once evolution is viewed as a branching tree. For the coelacanth, four points complicate the label:

A lineage is not a species. Latimeria chalumnae was new to science in 1938. The lineage is ancient; the species and the individual fish are not fossils.
The body kept changing. The 2024 analysis found that major new anatomical features essentially stopped appearing after the mid-Cretaceous, but body proportions and counted (meristic) traits continued to evolve at typical Mesozoic rates. In overall body shape and lower-jaw shape, Latimeria is quite distinct from Mesozoic coelacanths. Across the group's history, coelacanths evolved faster during periods of high global tectonic activity, which the authors suggest created new habitats.
The genome is not static. The 2013 study found slow protein-coding change but no sign that the genome as a whole lacks flexibility; about 25 percent of it consists of transposable elements, DNA sequences that can copy themselves. The authors suggested that a stable habitat and little predation over evolutionary time could explain the slower gene evolution.
Populations are still diverging. The two living species split millions of years ago, and NOAA describes the Tanzanian population of the West Indian Ocean coelacanth as having diverged from other populations about 200,000 years ago.

Two living species

The West Indian Ocean coelacanth lives off the Comoros and along the East African coast from Kenya to South Africa, and has been recorded off Madagascar. The second species was discovered in Indonesia in 1997. After a fisherman landed a coelacanth off Manado Tua, North Sulawesi, in July 1998, scientists from UC Berkeley and the University of Texas compared eight stretches of its DNA with those of Comoran coelacanths. They found a difference of about 4 percent, although they could not find a single physical feature that separated the two. They estimated that the species split 4–6 million years ago, possibly as long as 16 million years ago. A French-led team had already named the Indonesian species Latimeria menadoensis in 1999, after Manado Tua. The two populations are about 10,000 km (6,200 mi) apart.

The IUCN Red List classifies the West Indian Ocean coelacanth as Critically Endangered and the Indonesian coelacanth as Vulnerable. Both are caught accidentally by fishers.

Is the coelacanth our ancestor?

No. Coelacanths and land vertebrates both descend from lobe-finned fish, and the coelacanth genome is used to study the genetic changes that came with the move to land, including genes involved in the development of fins and limbs. But a living coelacanth is not a direct ancestor of amphibians, reptiles, birds, mammals or humans. Its genome confirms that lungfish, not coelacanths, are the closest living fish relatives of tetrapods. The coelacanth is a surviving side branch, and calling it a "missing link" replaces a branching tree with a ladder.

In summary

The coelacanth is called a living fossil because it was known only from fossils until 1938, it is the last branch of a lineage more than 410 million years old, and it shares many anatomical features with its Mesozoic relatives. The term describes that history; it is not evidence that the fish stopped evolving, since its body proportions, genes and populations have continued to change.

For the living fish's size, diet, depth, lifespan and how many are left, see the full coelacanth profile.