Crocodiles


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Crocodiles

 

(Crocodylia, or Loricata), an order of aquatic reptiles.

The majority of crocodiles measure 2–5 m, and some reach 6 m (the saltwater crocodile and old males). The head of the crocodile is flat, with a long snout and a characteristically curved mouth slit; the trunk is flattened, and the tail is powerful and compressed laterally like an oar; the legs are massive and relatively short. The eyes have a vertical-slit pupil and are placed very high. The nostrils and ear openings close by means of valves. The skin is thick and covered on the upper and lower sides of the trunk and tail with large, rectangular, horny plates. Under the dorsal plates, and in some species also under the ventral plates, lie thick bony plates that form an armor. The skull of the crocodile is characterized by the presence of two temporal arches and the immovable connection of the quadrate bone with the cranium. The nasopharyngeal passage is separated from the oral cavity by a secondary bony palate. Homotypic conical teeth are located in separate chambers and are replaced as they wear out. The vertebrae are procoelous. The ribs articulate with the vertebrae by means of a double capitulum, and each has hooklike process. There are “ventral ribs.” The shoulder girdle consists only of the scapula and the coracoid.

Crocodiles are higher than other reptiles in brain development. Of the sense organs, those of vision and hearing are especially well developed. The heart has two ventricles, which are completely separated by a septum (as in birds and mammals). At the site of the crossing of two aortic arches there is an opening between them through which blood may enter one arch from the other. The lungs are large and of complex structure. The fleshy tongue is attached to the floor of the oral cavity along its entire length. The stomach has thick muscular walls. There is no urinary bladder. The cloaca is in the form of a longitudinal slit, in the posterior part of which in males there is an unpaired sex organ; lateral to it lie the musk glands. The same type of glands are found on the lower side of the jaw.

Crocodiles are distributed in all tropical countries; they live in rivers, lakes, and marshes where there is an abundance of water; some live along the seacoasts. They are active predominantly at night. They feed mainly on fish and, in addition, on birds and mammals that live near the water and on aquatic mollusks and crustaceans; they attack large mammals (even cattle) at fords and drinking places. They dismember large prey on the shore by means of their powerful jaws and anterior extremities and swallow them in pieces. The crocodile’s voice, something between a bark and a roar, is especially often heard during the mating season. The female deposits the eggs in sand on the banks or buries them in a pile of rotting leaves of marsh plants. The number of eggs varies from 20 to 100. The eggs have a solid, white, calcareous shell. Females of a number of species stay near the clutch for a long time, guarding the eggs and subsequently the young from enemies. In some countries during periods of drought crocodiles bury themselves in the slime of drying bodies of water and hibernate until the rains come. Crocodiles cause some damage to livestock raising. Large crocodiles often attack man. Crocodile meat is edible and is used as food by the populations of many tropical countries. The skin of crocodiles, especially of alligators, is used for various products (briefcases, suitcases, saddles, etc.).

The crocodile order includes three families—the gavials, true crocodiles, and alligators. The alligator family includes seven species, belonging to the four genera Alligator, Caiman, Melanosuchus, and Paleosuchus; the latter three are combined under the general name of caimans. The family of true crocodiles has three genera. The genus Tomistoma includes a single species, the gavial crocodile (71 schlegelii ), with a length of up to 5 m. It is distributed in the rivers of the Malay Peninsula and on the islands of Sumatra and Kalimantan (Borneo). The genus of true crocodiles (Crocodylus) is found in all tropical countries and includes ten (or 14) species, including the Nile crocodile (C. niloticus), whose length is up to 7 m and which is distributed in the rivers, marshes, and lakes of tropical Africa, from Senegal and the Upper Nile to Natal and also on Madagascar; the salt-water crocodile (C. porosus) is distributed at the mouths of rivers and along the seashores of Southeast Asia and the islands of the Malay Archipelago and also of Northern Australia and New Guinea; it often swims into the open sea. The genus of dwarf crocodiles (Osteolaemus) includes two species; its length is up to 2 m; they are found in western Africa.

The rapacious extermination of crocodiles for the sake of their skins, which are used in the haberdashery industry, has led in recent years to a sharp decrease in the number of these animals. In a number of countries (the USA, Cuba, Japan) there are special farms where crocodiles are raised. Present-day crocodiles are the vestiges of a large group of crocodiles (which originated in the late Triassic from thecodonts), including up to 15 families and embracing about 100 genera; the majority of them died out at the beginning of the Cenozoic. Fossil remains of crocodiles have been found in Europe, Asia, and North and South America.

REFERENCES

Zhiznzhivotnykh, vol. 4, part 2. Moscow, 1969.
Osnovy paleontologii: Zemnovodnye, presmykaiushchiesia i ptitsy. Moscow, 1964.
Wermuth, H., and R. Mertens. Schildkröten. Krokodile. Brölckenechsen. Jena, 1961.

P. V. TERENT’EV

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