Coelacanths, the World's Only Living "Extinct" Fish

01
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How Much Do You Know About Coelacanths?

coelacanth
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You'd think it would be hard to miss a six-foot-long, 200-pound fish, but the discovery of a live Coelacanth in 1938 caused an international sensation. On the following slides, you'll discover 10 fascinating Coelacanth facts, ranging from when this fish supposedly went extinct to how the females of the genus give birth to live young.

02
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Most Coelacanths Went Extinct 65 Million Years Ago

coelacanth
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The prehistoric fish known as Coelacanths first appeared in the world's oceans during the late Devonian period (about 360 million years ago), and persisted all the way to the end of the Cretaceous, when they went extinct along with dinosaurs, pterosaurs and marine reptiles. Despite their 300-million-year track record, though, Coelacanths were never particularly abundant, especially compared to other families of prehistoric fish.

03
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A Living Coelacanth Was Discovered in 1938

coelacanth
Wikimedia Commons

The overwhelming majority of animals that go extinct manage to *stay* extinct. That's why scientists were so shocked when, in 1938, a sailing vessel dredged up a live Coelacanth from the Indian Ocean, near the coast of South Africa. This "living fossil" generated instant headlines around the world, and fueled hopes that somewhere, somehow, a population of Ankylosaurus or Pteranodon had escaped the end-Cretaceous extinction and survived to the present day.

04
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A Second Coelacanth Species Was Discovered in 1997

coelacanth
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Sadly, in the decades following the discovery of Latimeria chalumnae (as the first Coelacanth species was named), there were no reliable encounters with living, breathing tyrannosaurs or ceratopsians. In 1997, though, a second Coelacanth species, L. menadoensis, was discovered in Indonesia. Genetic analysis showed that the Indonesian Coelacanth differs significantly from the African species, though they may both have evolved from a common ancestor.

05
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Coelacanths Are Lobe-Finned, not Ray-Finned, Fish

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The vast majority of fish in the world's oceans, lakes and rivers--including salmon, tuna, goldfish and guppies--are "ray-finned" fish, or actinopterygians, the fins of which are supported by characteristic spines. Coelacanths, by contrast, are "lobe-finned" fish, or sarcopterygians, whose fins are supported by fleshy, stalklike structures rather than solid bone. Besides Coelacanths, the only extant sarcoptergians alive today are the lungfish of Africa, Australia and South America.

06
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Coelacanths Are Distantly Related to the First Tetrapods

tiktaalik
Tiktaalik, one of the first tetrapods (Alain Beneteau).

As rare as they are today, lobe-finned fish like Coelacanths constitute an important link in vertebrate evolution. About 400 million years ago, various populations of sarcopterygians evolved the ability to crawl out of the water and breathe on dry land. One of these brave tetrapods was ancestral to every land-dwelling vertebrate on earth today, including reptiles, birds and mammals--which all bear the characteristic five-toed body plan of their distant progenitor.

07
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Coelacanths Possess a Unique Hinge in Their Skulls

coelacanth
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Just how distinctive are Coelacanths? Well, both identified Latimeria species have heads that can pivot upwards, thanks to an "intracranial joint" on the top of the skull (an adaptation that allows these fish to open their mouths extra-wide in order to swallow prey). Not only is this feature lacking in other lobe-finned and ray-finned fish, but it hasn't been seen in any other vertebrates on earth, avian, marine or terrestrial, including sharks and snakes.

08
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Coelacanths Have a Notochord Beneath Their Spinal Cords

coelacanth
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Although Coelacanths are technically vertebrates, they still retain the hollow, fluid-filled "notochords" that existed in the earliest vertebrate ancestors. Other bizarre anatomical features of this fish include an electricity-detecting organ in the snout, a braincase consisting mostly of fat, and a tube-shaped heart. (The word Coelacanth, by the way, is Greek for "hollow spine," a reference to this fish's comparatively unremarkable fin rays.)

09
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Coelacanths Live Hundreds of Feet Beneath the Water

coelacanth
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As you might expect given their extreme rarity, Coelacanths tend to stay well out of sight. Both species of Latimeria live about 500 feet below the water (in the so-called "twilight zone"), preferably in small caves carved out of limestone deposits. It's impossible to know for sure, but the total Coelacanth population may number in the low thousands, making this one of the world's rarest and most endangered fish (even though its sparse numbers certainly can't be blamed on overfishing by humans!)

10
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Coelacanths Give Birth to Live Young

coelacanth
Wikimedia Commons

Like assorted other fish and reptiles, coelacanths are "ovoviviparous"--that is, the female's eggs are fertilized internally, and stay in the birth duct until they're ready to hatch. Technically, this type of "live birth" is different from that of placental mammals, where the developing embryo is attached to the mother via an umbilical cord. (While we're on the subject, one captured female Coelacanth was discovered to have 26 newborn hatchlings inside, each of them over a foot long!)

11
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Coelacanths Feed Mostly on Fish and Cephalopods

coelacanth
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The Coelacanth's "twilight zone" habitat is ideally suited to its sluggish metabolism: Latimeria isn't much of an active swimmer, preferring to drift along in deep-sea currents and gobble whatever smaller marine animals happen across its path. Unfortunately, the inherent laziness of Coelacanths makes them a prime target for larger marine predators, which explains why some Coelacanths observed in the wild sport prominent, shark-shaped bite wounds!