A coelacanth (pronounced SEE-luh-kanth) is a large, primitive fish found in the Indian Ocean. Described as a "living fossil" and once thought to be extinct, this deep-sea fish is believed to form one of the "missing links" in the evolution from fish to land animals.
Until December 1938, the coelacanth was known only by the fossil record that suggested it had lived as long as 350 million years ago in what is called the Devonian period, and that it probably went extinct some 70 million years ago. It was identified scientifically as part of the extinct sub-class of Crossopterygii (pronounced kross-op-teh-RIH-jee), which means a "lobe-finned fish." Until 1938, most scientists believed the coelacanth had disappeared along with the dinosaurs at the end of the Cretaceous (pronounced kree-TAY-shus) period. However, during that year, fisherman off the eastern coast of South Africa caught a 5-foot (1.5-meter) fish with deep-blue scales and bulging blue eyes that was strange enough to make them bring it to a local museum. The curator, Courtney Latimer, could not identify it, but knew that it was important enough to contact J. L. B. Smith, a leading South African ichthyologist (pronounced ik-thee-OL-low-jist), a zoologist who specializes in fishes. Smith then pronounced the fish to be a coelacanth, and this "living fossil" became the zoological find of the century. Soon after the discovery and publicity, other fisherman from nearby islands were reporting that they too had caught these strange fish that were not good to eat.
Extinct: No longer alive on Earth.
Missing link: An absent member needed to complete a series or resolve a problem.
One of the reasons that this discovery caused so much excitement was that in 1938 the coelacanth was thought to be a direct ancestor of tetrapods (pronounced TEH-truh-pods), or four-limbed land animals. This was believable because the coelacanth is unlike any other fish. Coelacanth means "hollow spine" in Greek, and, in fact, this strange creature seems to be a combination of two very different types of fish: those that are made of cartilage, like sharks, and all the other regular bony fishes. Its backbone is a long tube of cartilage instead of being a rigid backbone, yet it has a bony head, teeth, and scales. It is a carnivorous (pronounced kar-NIH-vor-us) predator—meaning that it catches, kills, and eats its live prey—and has impressive jaws and rows of small, sharp teeth. Most important, it has four muscular, limblike fins underneath its body that it uses like legs to perch or support itself on the ocean bottom. This led some to believe that it actually used these jointed fins to "walk" on the bottom like a four-legged animal. However, recent molecular analysis indicates that the lungfish, instead of the coelacanth, is genetically the closest living fish that is a relative of land animals.
Since that first discovery of a living coelacanth in 1938, additional coelacanths have been caught not only off the southern tip of Africa but off Sulawesi, Indonesia, as well, suggesting that they are more numerous than believed. Today's coelacanths are larger than those found as fossils, and they can grow to be more than 5 feet (1.5 meters) long and weigh as much as 180 pounds (82 kilograms). Scientists still do not know a great deal about them, and it was not until 1975 when a female was dissected that scientists learned that the coelacanth gives birth to live "pups." Zoologists believe that females do not reach sexual maturity until after 20 years of age and that the gestation (pronounced jes-TAY-shun) period, or the time it takes to develop a newborn, is about 13 months. Females give birth to between 5 and 25 pups, which are capable of surviving on their own after birth.
Although there are more coelacanths than at first supposed, they are still recognized as an endangered species. The main reason for this is that they are a highly specialized species that has adapted itself to a narrow habitat range. This means that they can only survive in the cool, deep waters—over 650 feet (200 meters) deep—around volcanic islands. Further, they are a highly specialized fish, resting in lava caves during the day and hunting and feeding at night. Although they move with slow, almost balletlike motion, they are excellent predators who can move surprisingly fast when they ambush a smaller fish for a meal. Along with the nautilus (pronounced NAW-tih-lus) and horseshoe crab, the coelacanth is one of the "living fossils" of the sea, since they have changed little from their ancient ancestors.
[ See also Fish ]