There are plenty of fish in the sea, but few are more astounding than the coelacanths—a group that defied extinction and turned the scientific world upside down.
1. COELACANTHS HAVE BEEN AROUND FOR AT LEAST 407 MILLION YEARS.
During the Devonian, which lasted from 416 to 358 million years ago, ferns evolved, trilobites still roamed the oceans, vertebrates took their first steps onto dry land, and fish began to diversify—hence the period's nickname, "the age of fish." The oldest-known coelacanth appeared in present-day Australia during this time, between 407 and 409 million years ago. Like modern coelacanths, the creature belonged to a group known as the sarcopterygians, or “fleshy-limbed vertebrates.” These animals are defined by their bony skeletons and fleshy, muscular fins that bear a striking resemblance to our own limbs. The similarity is no coincidence: By the end of the Devonian, the sarcopterygians would give rise to the first terrestrial vertebrates, which, in turn, begat the amphibians, the reptiles, and—eventually—mammals like us. Indeed, to modern biologists, humans aren’t descended from sarcopterygians, we actually are sarcopterygians.
2. THE WORD COELACANTH MEANS “HOLLOW SPINE.”
It’s a reference to the hollow, rod-like rays that are present in the creatures’ dorsal fins. The term coelacanth is descended from Coelacanthus granulatus, a name that zoologist Louis Agassiz gave to a prehistoric British species in the 1830s. As it happens, Coelacanthus granulatus was the first coelacanth to ever be scientifically described. Since then, over 120 additional species have been found—including those that are still alive today. (More about them later.)
3. THEY ONCE CAME IN ALL SHAPES AND SIZES.
After the Devonian, coelacanths flourished, evolving to fill an array of different niches. Many were slow-moving marine carnivores that must have ambushed passing prey items, but at least one fossil coelacanth was an active, speedy predator. Discovered in 2012, Rebellatrix divaricerca terrorized the seas that covered British Columbia around 250 million years ago. A sleek creature with a forked tail, the fish probably chased down smaller animals over great distances. Another notable species was Megalocoelacanthus, a toothless giant that grew to be 10 feet long. A few coelacanths left the ocean altogether and became freshwater denizens [PDF]. Some of these lake and river fish would have no doubt encountered the occasional dinosaur.
4. BEFORE 1938, IT WAS ASSUMED THAT ALL COELACANTHS WERE EXTINCT.
Coelacanths past and present constitute an entire order of fish—and for a century, paleontologists believed that the whole lot was wiped out in the same extinction that claimed the dinosaurs (birds notwithstanding) some 66 million years ago. But then, just a few days before Christmas in 1938, a trawler on the Indian Ocean caught a strange-looking fish in its nets. That vessel, the Nerine, was captained by Hendrik Goosen, though he took no notice of the odd beast he’d reeled in. The Nerine proceeded as usual to its destination: a fish market in East London, South Africa. Upon docking there, Goosen—as was his custom—called Marjorie Courtenay-Latimer.
Courtenay-Latimer, the curator of a local museum, had befriended the captain, who would always invite her to comb through his latest haul for odd-looking specimens. But on that day in 1938, she nearly turned him down—she had her hands full with a new fossil exhibit. In the end, Courtenay-Latimer decided to drop by anyway, if only to wish the crew a Merry Christmas.
She would later recount that "I picked away the layers of slime to reveal the most beautiful fish I had ever seen. It was 5 feet long, a pale, mauvy blue with faint flecks of whitish spots; it had an iridescent silver-blue-green sheen all over. It was covered in hard scales, and it had four limb-like fins and a strange little puppy dog tail. It was such a beautiful fish—more like a big china ornament—but I didn't know what it was.” Courtenay-Latimer recovered the corpse, stuffed it, and contacted renowned chemist and ichthyologist J.L.B. Smith. Two months later, he confirmed that her mystery fish was, in fact, a modern-day coelacanth. To honor its discoverer, Smith named the creature Latimeria chalumnae.
5. TWO LIVING SPECIES ARE NOW RECOGNIZED.
Latimeria chalumnae is commonly referred to as the West Indian Ocean coelacanth. Capable of reaching over 6 feet in length, this metallic-blue carnivore occupies the waters off of South Africa, Madagascar, Mozambique, and the Comoro Islands. A deep-sea creature by nature, West Indian Ocean coelacanths typically live at depths of around 300-1000 feet, but have been found at 2000 feet beneath the waves. Their hunting sessions mainly occur at night—during the day, the fish retire to undersea caves, where they hang out in groups of up to 16 individuals.
A smaller, brown-colored species called the Indonesian coelacanth (Latimeria menadoensis) came to light during the late 1990s. Relatively little is known about this elusive creature and only a handful of specimens have ever been documented. At present, both Latimeria species may be in trouble. The West Indian Ocean coelacanth is considered critically endangered and its Indonesian relative has been classified as vulnerable by the International Union for Conservation of Nature (IUCN). If both animals should go extinct, the whole coelacanth order will die out with them—this time, for real.
6. COELACANTHS HAVE A CRAZY MOUTH ...
Unlike any other animal that is presently alive, coelacanths have an intracranial joint behind the eyes that splits the skull in two, enabling the entire snout to swing upward when a coelacanth opens its mouth. The joint allows coelacanths to take disproportionately wide bites and, as biologist Hugo Dutel explains in this video, the joint and its corresponding muscles “[enhance] the overall bite force during the capture of prey.” Keep your fingers away from those teeth, folks.
7. ... AND VESTIGIAL LUNGS.
CT scans have shown that the embryos of these fish start growing lungs at an early point in their lengthy gestation period. Over time, however, a coelacanth’s lung development slows, and by the time it becomes an adult, the organs cease to serve any discernible purpose. Also noteworthy is the fact that flexible plates surround the useless lungs in full-grown Latimeria. Some coelacanth fossils exhibit similar structures.
8. FROM TIME TO TIME, THE FISH LIKE TO SWIM NOSE-DOWN.
Fast-forward to 0:55 in the above video and you’ll observe a curious display. On many occasions, wild coelacanths have been seen adopting what’s often described as a “headstand position.” For up to two full minutes, the fish angle themselves downward, holding their snouts perpendicular to the ocean floor. The maneuver’s purpose is a mystery, although some experts think that it may help the animals track their prey.
9. COELACANTHS MIGHT BE MONOGAMISTS.
Although the mechanics of coelacanth reproduction aren’t fully understood, we do know that their eggs are fertilized within the mother’s body. In 2013, a German team analyzed the corpses of two pregnant Latimeria chalumnae. DNA testing revealed that their unborn broods had each been sired by a single father. This revelation really caught the scientists off-guard.
“For both [of our specimens], it was clear that there was only one male involved,” Dr. Kathrin Lampert, a biologist who helped orchestrate the study, told New Scientist. Going into the tests, she and her colleagues fully expected to find that the eggs had been fertilized by many different males. After all, by breeding with several partners, a mother coelacanth could dramatically increase her clutch’s genetic diversity.
“Monogamous mating systems are most commonly found in species where the father provides parental care or where there is no opportunity for polygamy,” Lampert’s team noted in their report. Perhaps, they argue, female coelacanths save valuable energy by limiting themselves to just one mate per breeding season.
10. ADULTS GIVE A WHOLE NEW MEANING TO THE TERM “FAT-HEAD.”
As a coelacanth gets older, its brain tissue grows at a much slower rate than the rest of its body. In a full-grown adult, the brain itself fills less than 1.5 percent of the brain cavity. The remainder of that space is occupied by fat. Juveniles, meanwhile, have proportionately larger thinking organs and less fat in their braincases.
11. A PROMINENT HEMATOLOGIST ONCE WROTE A COELACANTH OPERETTA.
On September 10, 1975, a dead coelacanth that had been sitting in an aquarium at the American Museum of Natural History since 1962 was dissected. The decision to cut it up had been made when a hematologist named Charles Rand of Long Island University expressed an interest in acquiring some spleen samples. Together, Dr. Rand, paleontologist Bobb Schaeffer, and ichthyologists James Atz and C. Lavett Smith took a scalpel to the fish.
A huge surprise lay in wait beneath its skin. Within this deceased sarcopterygian, the astonished scientists found five embryonic coelacanths. These unborn babies revealed that, unlike most fish, the magnificent Latimeria chalumnae gives birth to live young.
Elated by the breakthrough, Rand started waxing poetic—or should we say operatic? With a parodic zeal that would do "Weird Al" Yankovic proud, the musically-inclined hematologist wrote some lyrics for a new operetta titled A Coelacanth’s Lament, or Quintuplets at 50 Fathoms Can Be Fun. His rhymes were set to the melody of various Gilbert and Sullivan songs, including “Tit Willow” from their 1885 comedic masterpiece The Mikado. Fortunately for all of us, the AMNH has been good enough to upload a few of Rand’s verses. Enjoy.