CROCODILE, a name applicable to any member of the reptilian order Loricata (Crocodilia) but often restricted to species of the genera Crocodylus and Osteolaemus in contrast with the alligators (genera Alligator and Caiman). The order con tains only 21 living species but the geological history of the group can be traced back at least as far as Jurassic times (see REPTILES).
They are the largest living reptiles but it is difficult to be sure of their maximum size owing to the number of exaggerated stories which obtain currency. The largest species is the salt-water or estuarine crocodile (C. porosus) which has been reported to at tain a length of 33 ft., and the smallest, one of the South Ameri can caimans (Cayman palpebrosus) which scarcely attains a length of 4 ft. Very large specimens of any species are undoubtedly be coming more and more rare ; modern arms are too well dis tributed for many very old individuals to survive.
On account of the interest taken in crocodiles because of their size, their dangerous nature and the trophies which they yield to the sportsman, a key, based on characters of the head and skull, is given by means of which a specimen may be identified at least as far as its genus.
I. Snout very long and slender; the halves of the lower jaw fused in front as far back as the I 5th tooth.
(a) 27-29 teeth on each side of the upper jaw. Gavialis (the gharial of N. India).
II. Snout triangular or rounded; the halves of the lower jaw not fused farther back than the eighth tooth.
(a) The fourth tooth of the lower jaw fits into a notch in the side of the upper jaw. Crocodiles.
(I) Nasal bones dividing the nasal aperture into two. Crocodylus (Africa to south China, north Australia and the Fiji Islands; southern United States to Venezuela and Ecuador) .
(2) Nasal bones not dividing the nasal aperture; snout turned up in front. Osteolaemus (W. Africa).
(3) Nasal bones not dividing the nasal aperture; snout not turned up. Osteoblepharon (Congo).
(b) The fourth tooth of the lower jaw fits into a pit in the upper jaw. Alligators.
(I) Nasal bones dividing the nasal aperture Alligator (southern United States and south China).
(2) Nasal bones not dividing the nasal aperture Caiman (Tropical South America).
The two first-mentioned genera, each possessing but a single species, are highly specialized fish-eating forms, the long, slender snout and numerous, sharp, interlocking teeth forming an efficient fish-catching mechanism. The remaining genera are much broad er-snouted and, though fish form their staple food, they will also eat anything they can overpower; lying idly in the water with only the nostrils, eyes and perhaps part of the back showing they look like floating logs and any unwary bird or beast approaching within range of the powerful jaws is seized, dragged under water and eaten. There are undoubtedly occasional man-eaters but generally they recognize man as their chief enemy and become wary and difficult to approach.
All the species reproduce by means of eggs. The sexes are able to find one another by hearing and by smell; during the mating season the males, at least, exercise their vocal powers, the call varying with the species but usually being an intermittent bellow which may be heard for a considerable distance. Both sexes are provided with two pairs of scent glands ; one pair lies at the sides of the throat and the other inside the cloaca. The glands on the throat are normally only visible as a pair of small slits but excitement may cause them to be turned inside out so that they appear as rounded excrescences. Both pairs of glands are close to the soil when the animal is at rest on the bottom or basking on the shore and their secretion, which has a strong musky odour, leaves a trail that can be followed by other mem bers of the species. The eggs are white, oval, covered with a thick calcareous shell and are laid on land; the number in a clutch varies according to the size of the individual and may vary from 20 to 9o. The site and type of "nest" vary somewhat in different forms but the eggs are never incubated by either parent. The Nile crocodile (C. niloticus) deposits its eggs in the sand, the hole being from IS in. to 2 ft. deep and the eggs arranged in two layers with a layer of sand between. Many other species including the West African croc odile (C. cataphractus) and the North American alligator (A.
mississipiensis), sweep together a mound of vegetable trash and deposit the eggs in the centre of this pile. Incubation is carried out chiefly by the heat of the sun but in the second case the heat of fermentation of the vegetable matter probably assists; the mother remains in the vicinity of the nest, visiting it from time to time and, warned by the hic cough-like cries which the young produce when ready to leave the egg, scratches away the covering of the nest and conducts her brood to the water. The young are able to break their way through the strong egg-shell by means of an "egg-tooth" which develops on the tip of the snout but which is lost soon after hatching; they are two or three times as long as the eggs from which they emerge and are at once able to fend for themselves.
Growth is fairly rapid, usually about a foot a year under able conditions for the first few years and more slowly thereafter.
The habits of all, whether crocodiles or alligators, are very similar. They are essentially aquatic, living, as a rule in sluggish streams and lakes, and swim by powerful strokes of the flattened tail, the limbs being folded against the body. But their powers of locomotion on land are not to be despised. Ordinarily their progress is a mere crawl, the body and tail being dragged along, but when excited they can run at quite a considerable pace with the body held well off the ground. Much of their time is spent basking in the full glare of the sun on sandbanks, often with the mouth agape, and it is when the Nile crocodile is so engaged that a species of plover (Pluvianus aegyptius) may be seen picking parasites from among the reptile's teeth ; possibly the crocodile extends a tolerance to these birds in exchange for the warning which their cries give as they fly away on the approach of danger. Some species hibernate buried in the mud during the colder parts of the year and others may aestivate in the same manner during the dry season when the rivers and pools dry up; it is not un usual, however, for them to undertake long migrations overland when in search of new quarters and there are records of the in vasion of a town by numbers of the Indian crocodiles (mugger or marsh crocodile, C. palustris) which had been compelled to leave their water-hole by a severe drought.
The salt-water crocodile (C. porosus) has the most extensive range, being found from Bengal to southern China, northern Australia and the Fiji islands and this species is the only one which is ever found at sea; the remaining species frequent fresh waters only. The genus Crocodylus ranges from west Africa to Central America; the best known species are the 1iile crocodile which, though formerly plentiful is now rare in lower Egypt and which extends southwards to Rhodesia, the mugger of the Indian region; the North American crocodile (C. acutus) which occurs throughout the West Indies and from the southern United States to Colombia, and the Orinoco crocodile (C. intermedius). The genus Alligator occurs only in the southern United States. (A. mississipiensis) and southern China (A. sinensis) and the caimans (5 species) are confined to South America.
These creatures have a definite economic value, their hides being in demand for the making of fancy leathers; this has led to considerable slaughter and great reduction in the numbers of many species. So far has this gone in North America that alli gator "farms" have been established; since, however, it takes at least four years to produce a hide which has a marketable value, the financial success of the farms depends at least as much on the sale of curios as on the production of leather. See also