Coelacanth

The Coelacanth is a huge prehistoric fish that can measure nearly 6 feet long and weigh around 200 pounds and which lived around the same time as the dinosaurs. It appeared in the oceans of the world about 360 million years ago during the Upper Devonian period and died out almost at the same time as the dinosaurs, pterosaurs and marine reptiles at the end of the Cretaceous period. Nowadays, Coelacanth is an extremely rare fish that is very difficult to observe and whose population is estimated at only a few thousand individuals. For this reason, Coelacanth is ranked among the most endangered fishes.

Rare observations

Observations of Coelacanths are unusual because not only populations of this species are very small but in addition this fish prefers to remain well out of sight and hide in small underwater caves dugged up in the limestone deposits, 500 feet under the surface of the water in the twilight zone. In 1938, scientists were shocked when a sailing boat dredged up a living Coelacanth from the waters of the Indian Ocean near the South African coast. This extraordinary take instantly generated a global media wave and rekindled the hope that other prehistoric creatures could also have survived the massive Cretaceous-Tertiary extinction.

This first species, named Latimeria chalumnae, is one of two discoveries of Coelacanth made during the last hundred years. In 1997, at the turn of the 20th century, a second species was discovered in Indonesian waters. The genetic analyzes carried out by researchers have shown that Latimeria menadoensis differs greatly from the African species although they almost certainly have a common ancestor.

Lobe-Finned fish

Ray-finned vs Lobe-finned

With the lungfish found in Africa, Australia and South America, the Coelacanth is in a class of its own because it is a lobe-finned or sarcopterygian fish. Unlike the vast majority of modern fish (such as salmon, tuna, goldfish, guppy) that are ray-finned or actinopterygian, the fins of lobe-finned fishes are supported by a fleshy structure rather than a bony one.

Although these types of fish are now extremely rare, they nonetheless constitute an important link in the evolution of vertebrates. Hundreds of millions of years ago, many sarcopterygian populations began to crawl out of the water and breathe on land. Some of these prehistoric tetrapods are the direct ancestors of all terrestrial vertebrates known today as reptiles, birds and mammals.

Sluggish metabolism

Coelacanth is a lethargic fish that prefers to get carried away by deep ocean currents and swallow small marine animals, like other fish and cephalopods, that it encounters on its way rather than actively swimming and hunting. These "lazy" habits, however, make the Coelacanth a prime target for larger aquatic predators such as sharks that do not miss the opportunity to feed on it when they occur.

A unique adaptation of the Coelacanth to this apathetic way of life is that the latter is able to turn its head up and open its mouth very large (a bit like snakes) to swallow prey. This mode of feeding similar to that of the whale shark is facilitated by an intracranial joint located on the top of its skull. This feature is unique to Coelacanth and is not present in any other vertebrate, whether marine, avian or terrestrial.

Other strange features

In addition to its head that can rotate 90 degrees vertically, the Coelacanth has some other bizarre anatomical features such as an organ in the muzzle that detects electric fields, a cranium box filled with fat, and a tube-shaped heart.

Ovoviviparous

Like many other species of fish, the Coelacanth is ovoviviparous: the eggs are fertilized inside the female and remain in the birth canal until they are ready to hatch. This mode of birth is distinguished from that of placental mammals in which the embryo is attached to the mother by an umbilical cord.