These strange creatures are among the most fascinating oddities on earth. Their forerunners, the ancient fringe-finned fishes (crossopterygians) were at one time the chief animals of prey in fresh water. There were great numbers of them, and they thrived for untold ages.
But they died out millions of years ago. Or that, in any event, was the opinion of scientists until two were discovered alive in ocean waters quite recently.
Why should we dwell on these fishes of ages past? They are of great scientific interest, since it was from them that all land animals with backbones – the amphibians, reptiles, birds, and mammals – developed.
In these ancient types, we find that the paired fins, and sometimes the other fins, too, consist of fringed lobes. The rays and membrane of the fins are attached to a fleshy, scale-covered base, which contains supporting bones. These bones are so arranged that with relatively little change they could have become the support of a limb instead of a fin. Many fossil fringe-fins used the air bladder as a lung to breathe atmospheric air. These are two reasons why we believe the fringe-fins were the ancestors of the first backboned land animals, the amphibians.
The lungfishes are in several ways similar to the fringe-fins, but differ from them in the way the jaws are attached to the skull and in other characteristics. After studying the lungfishes and comparing them with fossils, some experts have come to the conclusion that the lungfishes are an offshoot of the fringe-fins that has become degenerate in a number of ways.
Lungfishes have lobe-shaped paired fins, which may, however, be no more than mere ribbon-like structures, as in the African and South American species living today. They also have nostrils that open into the cavity of the mouth and an air-bladder that serves as a lung. Strangely enough, they do not breathe air through their nostrils, however, apparently using them only for smelling underwater. Many of the internal structures of the lungfishes resemble the ones in amphibians.
The lungfishes of today are but a remnant of those that lived in the past. Five species are still alive, all inhabiting tropical fresh waters. Three very similar forms come from Africa, one from the Amazon and Paraguay Rivers of South America, and one from Queensland, Australia.
The East London Coelacanth, Latimeria chalumnae, was unknown until 1938, when a fishing boat off the coast of South Africa pulled in a five-foot, blue, rough-scaled fish with strange, fleshy bases to several of its fins and a peculiar triangle-shaped tail. Although the boat crew decided to save the queer fish, they did not realize the sensational nature of their unique catch..
As it turned out, the fish belonged to a group supposed to have become extinct sixty to seventy million years ago – about the same time that the dinosaurs disappeared from the earth. Through an unfortunate series of circumstances all of the internal soft parts and much of the skeleton of the East London coelacanth were discarded before it was examined by any expert. Therefore, strangely enough, the anatomy of some of its fossil relatives is better known.
As a result of the first catch in 1938, an intense search was started for more specimens, in the hope that we might learn more about this “living fossil.” In late 1952 fishermen took another coelacanth, and Professor J. L. B. Smith, leading South African ichthyologist, was rushed by plane to the scene of the find. He succeeded in The East London coelacanth belongs to a group of fishes that was supposed to have become extinct from sixty to seventy million years ago. In 1938, a fishing boat off the coast of South Africa pulled in a five-foot, rough-scaled specimen. Late in 1952, a native fisherman caught another coelacanth of a different species in the same general region. Both finds caused a great stir in the scientific world by preserving the specimen, to the delight of the scientific world. Most surprising of all, the fish turned out to be a different species. Scientists are now wondering more than ever what rarities still remain undiscovered in the depths of the sea.
The African Lungfish, Protopterus annectens, has been known to live longer without food and water than any other backboned animal. Specimens have been kept alive in a natural state of suspended animation in blocks of hardened mud for more than four years, after which they were “awakened” successfully to take up a more ordinary life for a fish. When the waters of its native tropical streams, lakes, and swamps commence to dry up during times of unusual drought or during regular annual dry seasons, the lungfish sinks into the mud. Being an air-breather, it is little inconvenienced so long as the mud remains quite soft; but when it begins to harden, the fish has to struggle to the surface to obtain a gulp of air. Nevertheless, the lungfish continues to force its way upward periodically, until at last the surface has become quite hard, and all that remains to indicate the fish’s presence is a breathing hole scarcely larger in diameter than a lead pencil.
Underneath in the still pliable mud, the lungfish now prepares itself for its summer rest, or “estivation,” as it is called. It folds its tail over its head, coming to rest in a tight U-shaped position, head and tail uppermost. Its skin secretes a thin covering, protecting all but the mouth of the fish against undue drying out. The mud gradually hardens all around it, and finally it is completely encased as if in stone. Profound changes in the working of the body parts of the immobile
The African lungfish provides us with a remarkable example of an animal that can live for a long period of time in a natural state of suspended animation. Some lungfish have existed in blocks of hardened mud for more than four years, and have afterwards resumed their usual life. Normally, lungfish must come to the surface for air, or drown. lungfish take place, enabling it to live at a very slow rate, so to speak, and to withstand the accumulation of waste products in its blood. When the rains return and soften the hardened mud, the fish is aroused from its “sleep” and soon begins to feed voraciously, principally on other fishes and on snails and bivalves.
The lungfish has small gills, but must have access to air or it drowns. About once every twenty minutes it comes to the surface to swallow a gulp of air, passing the gas into a pair of air bladders or lungs that open into the gullet. Among the many other unusual features of structure found in the lungfish are a pair of nostrils that open from the exterior into the mouth; in this respect lungfish differ from almost all other kinds of fishes. The lungfish has a long body with long dorsal and anal fins that seem to come together in a sharp point to form the tail. The pectoral and pelvic fins are merely long, tapering ribbons. Scales are small and completely embedded in the skin. In color it is brown or tan with black or dark brown mottling.
The male lungfish prepares a clear area among dense plant growth on the muddy bottom, and there the female lays her eggs. These are about one-eighth of an inch in diameter and are guarded by the male and kept supplied with fresh water by vigorous movements of his tail. After about eight days they hatch, and the young are also guarded for awhile. Young lungfish are unusual in having external gills – four pairs of them – like those seen in a number of amphibians. As the fish mature, these organs gradually disappear.
Lungfish attain a size of at least three feet. They are a popular food with native Africans. The African lungfish is widely distributed in the fresh waters of tropical Africa. There are two other closely related African species, one of which reaches a length of at least six feet.