CROCODILES AND ALLIGATORS
These repulsive and ferocious reptiles (Crocodilia) are the bulkiest of the whole class, and most resemble the ancient aquatic dinosaurs, with which they are undoubtedly allied, although their precise derivation is undetermined. Their general shape is in conformity with the reptilian model, rather than indicative of any close relationship to lizards; indeed their closest living relatives are the tuatara and the chelonians. They have four legs of nearly equal size in modern examples, but in some of the older extinct forms of the Lias and Jurassic strata the hind legs were much longer than the fore pair, and broadly webbed, while other features indicate a purely marine life; but it appears plain that the crocodilians originated as land dwellers whose descendants, early in the history of the group, took to an amphibious method of life.
The eyes, nostrils, and external ears are situated on the upper surface of the head, so that breathing, seeing, and hearing are unimpaired in the water, the upper part of the head being usually raised above the surface when swimming. The nostrils and ears have valves which are shut when the animal is under water.
Crocodiles and alligators are mainly carnivorous, feeding on mammals and waterfowl, for which they lie in wait close to the edge of the water, sweeping them in by a blow of their tail, but the gavials feed almost exclusively on fish. All are oviparous, laying oval, hard-shelled eggs.
The order is represented by a single family, Crocodilidæ, including six genera scattered through the tropical and subtropical parts of the globe in the strange fashion that characterizes many of the ancient groups of which present species are mere relics. Thus the American genus of alligators has also a species in China; and the Old World crocodiles are represented by a single, narrowly restricted species in the region of the Gulf of Mexico. Our common alligator (A. mississippiensis) inhabits the low coastal rivers and swamps from North Carolina to the Rio Grande, and remains abundant in the steaming bayous along the lower Mississippi, and in the swamps of Louisiana, but in Florida has been killed off, not only by the demand for its hide (as leather), but in a wanton way by tourists and sportsmen, until now its numbers are greatly reduced. It would have become nearly extinct were not its prolificness great, each female depositing thirty-five to forty eggs in the layers of the cone-shaped heap of a nest she makes on the bank.
Young alligators feed mainly on fish, but the old ones take more and more to getting birds and beasts for their dinner, stealing on them quietly as they swim, or when they approach the water to drink. The prey is dragged down and drowned. In the crocodilian throat the passage for air from the nostrils reaches much farther back above the mouth than in other animals, and the entrance of the windpipe may be closed by pressing together the base of the tongue and the soft palate, enabling the alligator to drown its prey without drowning itself. In two particulars our alligator is singular—its fear of man and its voice. When surprised basking on shore, as it likes to do, it will rush with awkward haste for the water; and there will get away or out of sight whenever a man appears. Hence it is safe to bathe in waters infested by alligators, which will retreat from the feared bather as far as possible. Nevertheless when an alligator is cornered it can and will make a very dangerous fight with jaws and tail that are truly formidable. But it rarely attacks unprovoked, except where a mother finds you tampering with her nest. As to its noise-making, the alligator is unique among reptiles in giving voice to a really loud noise, or bellow, which may sometimes be heard for a mile or more. It varies according to the size of the reptile from the gentle "mooing" of a small one to a "thundering and tremendous blast" by a big male.
In the half-submerged morasses of Florida, from Lake Worth southward, dwells a true crocodile, closely allied to that of the Nile, and first discovered there by William T. Hornaday in 1875. It differs from the alligator in the pattern of scales, in the relative length and vertical flatness of the tail, and especially in having a long, pointed snout instead of the broad, spade-shaped head of the alligator. Its general habits present no novelty, but it is more agile and, in captivity, more vicious than its cousin, while showing a similar dread of man in its wild home. This crocodile is found from northeastern Mexico south to the coast of Ecuador, especially in salt marshes.
Central and South America are the habitat of several species of caymans, which differ from alligators mainly in their teeth and the fact that protective scales cover the belly; they are blackish in color, and vary in size and markings, the largest, known on the Amazon as the black cayman, or "jacare usassu," growing to be twenty feet long; but the Indians pay little attention to it.
Crocodiles proper (genus Crocodilus) are distinguished by the fact that some of their foremost teeth fit into a notch of the upper lip, and are therefore exposed, as is not the case with alligators or gavials. One species lives in West Africa, another in India, another is wholly marine in habits (as were some of its extinct progenitors) and ranges from eastern India and southern China to northern Australia, a fourth is Australian, and a fifth Central American; but the best known of all is the so-called Nilotic crocodile of the upper Nile and the rivers of east central Africa. Formerly it occupied the whole course of the Nile, and was one of the sacred animals of the priestcraft of ancient Egypt. In Madagascar it is extraordinarily abundant, and has there the peculiar habit of digging long, ventilated burrows in the river bank, in which it lies, and where it stores its prey. Large old specimens may become fifteen feet in length, and their life is probably very long, for new teeth grow as fast as the old ones are lost, and when adult they have no known enemies except one another, but their eggs are sought for by several kinds of birds, lizards, and so forth, and the old ones devour many infants.
Crocodiles abound in all the sluggish rivers and estuaries of central Africa, and are more destructive of human life than even lions or leopards, and kill much game and many domestic animals. Lying in wait close to the bank, they make a rush, seize by the nose or leg any animal as it stoops to drink; or, stealing close to an antelope or goat standing at the edge of the river, they will, with a sweep of the tail, knock it into the water, and grasping it with their jaws bear it down to a horrible death. The crocodile does not at once tear its victim to pieces, as do the alligators, but pushes it into some hole in the bank to decompose before being consumed. Major J. Stevenson-Huntington says:
"At Sheshike, on the Zambezi, a paramount chief, who lived some forty years ago, used to derive great amusement from watching slaves and criminals being thrown to the crocodiles, his chair being brought to the river's bank in the cool of the afternoon that he might enjoy the spectacle in comfort. The crocodiles at this place never forgot those halcyon days, and, until very recently, it was almost certain death for anyone to drink at the river, or attempt to draw water, except within one of the protecting screens of logs which were erected for the purpose.... On the other hand there are some large pans in Amatongaland, which, although full of the reptiles, are said to be quite safe to bathe in, attacks on human beings being unknown.... Always cunning and suspicious, the crocodile at times evinces considerable audacity in the pursuit of his prey. Natives are occasionally knocked off the gunwales of their canoes by a flick from the tail. I recollect Major Gibbons, standing upright in the stern of our little aluminum steam launch on the Zambezi, with the tiller between his feet, nearly losing his balance through an attack of this kind. I have heard of a native, sleeping on a hot night in the doorway of a hut close to the river, being attacked and dragged in."
Despite this frequent attack on large prey, fishes are the main reliance of the African crocodiles for subsistence.
As opposed to this terrifying record from eastern Africa, the "long-snouted" crocodile of the west coast rivers offers a mild reputation, since it is content with fish, frogs and water birds as food, and fears men more than it is feared by them. The natives hunt it for the sake of its flesh. Crocodile meat is considered good in all uncivilized parts of the world, but most white men dislike its musky flavor; the same may be said of the eggs of these reptiles.
The Orient possesses a variety of crocodiles, the best known of which are the marsh crocodile, a near relative of the African species, and the gavial, placed in the genus Gavialis, and distinguished by its long, slender snout and weak teeth. This gavial abounds in the Ganges and other rivers of northern India and Burma, where it is numerous, and frequently exceeds twenty feet in length. A second species is found in the Malayan archipelago. It feeds almost exclusively on fish, and so rarely harms man or beast that it is regarded as harmless. The marsh crocodile, or "mugger," is also of great size, and inhabits the rivers and marshes of India, Ceylon, and the Malayan islands. It is a fish eater and an arrant coward, feared by no one under ordinary conditions. It was, perhaps, originally, as a matter of gratitude for this harmlessness, that the custom arose among the Hindus of venerating this reptile. In some places, as notably near Karachi, large numbers of muggers are kept captive in ponds, and attended by priests and devotees who guard and feed them.
A third species is the formidable "estuarine" crocodile, which frequents the tidal portions of rivers from the Bay of Bengal to China and Australia. It exceeds all of its race in stature, usually exceeding twenty feet long, and one old specimen on record was thirty-three feet from tip to tip. It is held in great fear by fishermen, for in many cases it develops man-eater proclivities, and has all the ferocity and resourcefulness of its Nilotic cousin. The salt-water habitat of this species recalls the fact that among the many kinds of fossil crocodilians known, from the Lias onward, one was a purely marine form.
The crocodiles are followed in the classification of the reptiles by several extinct groups, known only as fossils of the Mesozoic Age. The first of these is the subclass Plesiosauria, containing a series of predatory creatures characterized by very long necks, short tails, and feet that in the older forms indicate a terrestrial existence, but later exhibit a progressive change to paddles, showing that finally the plesiosaurs were wholly aquatic. This was accompanied by a steady increase in size, until finally a length of at least forty-five feet was reached—chiefly by extension of the neck—in the elasmosaurus of the Cretaceous rocks of Kansas.
Another subclass, Ichthyosauria, restricted to the Mesozoic Age, were large, swimming, marine "fish lizards" with a somewhat whalelike form, the front limbs transformed into paddles, and the snout in the form of a long bill filled with sharp teeth. They lived on fishes, cuttlefish, mollusks, etc., and had the general habits of sharks. They died out early in the Cretaceous epoch, and left no descendants.
A third extinct subclass is that of the pterodactyls, or "flying dragons" (Pterosauria), which possessed the air throughout the Mesozoic Age, and filled the place of birds in the fauna of that period, although they had no relationship to the real birds that came later. Some were no larger than sparrows, but later ones spread their leathery wings twenty feet or more. The origin and real affinities of these winged reptiles are unknown and they left no descendants.
We find in the Cretaceous formations skeletons of very long, slender marine reptiles (Pythonomorpha) with a lizardlike head and all four limbs in the form of paddles, of which the mososaurs are the best known. These were the latest of the Mesozoic reptiles; and about the time of their disappearance we begin to find the earliest fossil suggestions of the subclass Sauria which contains our modern orders Lacertilia, the lizards, and Ophidia, the serpents. Neither of these owe their ancestry to any of the fossil groups just mentioned, in spite of superficial resemblances, but "their origin has probably to be looked for among the Prosauria, of which Sphenodon (the tuatara, [see page 183]) is the only surviving member." They are also very distinct from crocodiles in structure.
| MESOZOIC FLYING REPTILE (PTERODACTYL) |
| (Restoration, after Owen) |