CROCODILE

The Nile crocodile (Crocodilus niloticus), in spite of its name, is found throughout much of any member of the reptile order Crocodilia. They are generally large, ponderous, amphibious animals, somewhat lizardlike in appearance, and carnivorous in habit. They have powerful jaws with many conical teeth and short legs with clawed, webbed toes. The tail is long and massive and the skin thick and plated. About 20 species are recognized. The group is of particular interest because of its evolutionary position: the crocodiles are the last living link with the dinosaur-like reptiles of prehistoric times. They are, at the same time, the nearest living relatives of the birds. A large variety of crocodile fossils have been discovered; three of the four suborders of Crocodilia are extinct. On the basis of this extensive fossil record, it has been possible to establish well-defined relationships between the crocodiles and other vertebrate groups. The Nile crocodile (Crocodilus niloticus), in spite of its name, is found throughout much of any reptile of the family Crocodilidae; the similar name crocodilian is applied to any of the Crocodiliaalligators, caimans, and gavials, as well as true crocodiles. Crocodiles are tropical reptiles found in Asia, the Australian region, Africa, Madagascar, and the Americas. Like other crocodilians, they are long-snouted, lizardlike, and carnivorous. Most feed on fishes, turtles, birds, and mammals; large individuals may attack domestic livestock or humans. Crocodiles swim and feed in the water but emerge onto land to bask in the sun and to breed. They frequently float at the surface of the water; in this position they wait for potential prey, often a small mammal, to come to the water's edge to drink. Crocodiles reproduce by hard-shelled eggs that are laid in nests built by the female. Baby crocodiles usually feed on insects and other small invertebrates. The diet changes as the crocodiles grow, gradually including more vertebrates and larger prey. Crocodiles have narrower snouts than alligators, and the fourth tooth in each side of the lower jaw is visible when the mouth is closed. They are reputed to be livelier than alligators and more likely to attack humans. There are about a dozen species of crocodiles, almost all of which are of the genus Crocodilus. Additional reading M.M. Cohen and C. Gans, The Chromosomes of the Order Crocodilia, Cytogenetics, 9:81105 (1970), pictures of karyotypes of all recent species of crocodiles and an attempt to interpret them from the viewpoint of evolution; H.B. Cott, Scientific Results of an Inquiry into the Ecology and Economic Status of the Nile Crocodile (Crocodilus niloticus) in Uganda and Northern Rhodesia, Trans. Zool. Soc. Lond., 29:211356 (1961), one of the most comprehensive accounts of the behaviour and territorialism of the Nile crocodile; O. Kuhn, Die vorzeitlichen Krokodile (1968), a survey of all recent and fossil crocodiles and a proposal of a common classification for both; F.J. Medem, The Crocodilian Genus Paleosuchus, Fieldiana, Zool., 39: 227247 (1958), the first comprehensive field work on smooth-fronted caimans, especially on their ecology; W.T. Neill, The Last of the Ruling Reptiles: Alligators, Crocodiles, and Their Kin (1971), a richly illustrated and extremely careful compendium of the biology of all recent crocodiles; A.S. Romer, Vertebrate Paleontology, 3rd ed. (1966), the classic work on the classification and phylogeny of the vertebrates and their mutual relations; A.D. Walker, A Revision of the Jurassic Reptile Hallopus victor (Marsh), with Remarks on the Classification of Crocodiles, Phil. Trans. R. Soc., Series B, 257:323372 (1970), a discussion of the division of crocodiles (Crocodilomorpha) in the suborders Crocodilia and Paracrocodilia based on anatomical examination of some fossil forms; H. Wermuth, Systematik der rezenten Krokodile, Mitt. Zool. Mus. Berl., 29:375514 (1950), a review of recent crocodiles and a discussion of the taxonomic importance of their characteristics, with figures of heads and skulls of all species; Farbwechsel und Lernfhigkeit bei Krokodilen, Dt. Aquar.-Terrar.-Z., 16:9092 (1963), observations on the intelligence of a tame, seven-foot, spectacled caiman; O. von Wettstein, Crocodilia, Handb. Zool., 7:236424 (1931), a complete monograph of the recent crocodiles, with an extensive bibliography.