LIZARD, a subclass of reptiles, whose anatomical features and classification have been described under Lacertilia. A general account of their habits and ecology has been reserved for the present article. Lizards as a group are of comparatively recent origin, most of the fossils known not being older than the middle of the Tertiary, when representatives of many of the modern genera were in existence. The Pleistocene rocks of Queensland have furnished skeletons of several gigantic extinct representatives of the monitor family, one of which (Megalonia) was about 30 feet long. The lizards, as a group, are remarkable for the great variety in size and shape, and in the character of the skin-armature and the dentition. These variations are usually manifestly adaptations to the local environment.
Lizards abound in all the warmer parts of the world, most numerously in the tropics. In North America only three or four species pass the northern boundary of the United States, penetrating southern Ontario in the east and British Columbia on the Pacific side of the continent, where, in the arid Southwest, most of the species known in this country are to be seen. Most kinds of lizards are restricted in range, being adapted to a definite sort of environment, yet the families may have a very wide distribution. Thus that of the geckos (q.v.) is spread all over the tropical and subtropical zone of the Old World, and also in South America; and it includes both arboreal and terrestrial forms, diversified by modifications of the type to meet conditions as different as are the steaming jungles of Malaya from the sandy deserts of Persia and Africa. On the other hand the big monitors (Varanidæ), scattered from the Nile to the Philippines and Australia, are able to seek their prey on burning desert-ground, in and under water, and among the branches of forest-trees. This is a case of remarkable versatility, for there is little adaptive alteration of structure in the family. Again, similarity of habitat and local influence sometimes produce striking likeness in appearance in totally disconnected species, as, for example, our spiny-coated horned toads and the Australian molochs (q.v.), which are not at all related structurally. A large number of lizards belonging to widely different families have taken to a more or less complete underground life; and in these the limbs show reduction from a slight degree in some to entire absence in others, for instance the boa-like glass-snake (q.v.). Many species are good swimmers, and are of aquatic habit to a large extent, but only one truly marine species is known — the large, gregarious sea-lizard (Amblyrhynchus) of the Galapagos Islands, which feeds on seaweed, gathered at a considerable depth; yet it is reluctant to take to the water except for food. The American iguanas, however, although habitually residents of tree-tops, stay as near to rivers as they can, and plunge into them for safety whenever frightened.
Lizards are primarily terrestrial animals, and most sorts run with amazing swiftness, usually on all four feet, but the curious frilled lizard (q.v.) of Australia holds up its fore parts and runs on its hind legs when in haste. Except a few heavy forms, and those that dwell in burrows, lizards are extremely agile, climbing walls and tree-trunks, and running and leaping about their branches, with speed and precision; and some Oriental species, as the flying dragon (q.v.), have expansions of the skin about the forearms enabling them to make long, sailing leaps through the air.
The senses of sight and hearing are highly developed, as is requisite for their livelihood. Most species are carnivorous, the larger kinds feeding on small mammals, birds and their eggs, and the lesser reptiles, including other lizards. These are seized by a rush and leap, and are passed down the throat whole. Many of the smaller kinds live altogether on worms and insects, the latter caught in most cases by a swift dart and recovery of the sticky tongue, a method peculiarly characteristic of the chameleons (q.v.). The tongue in this group assumes a wide variety of shapes, in some families having a slender, forked form like that in snakes, and acting only as a feeler. One lizard only, the Gila monster (q.v ), is aided by the injection of poison into its victim when he bites it, and this is the most sluggish of all its race. The iguana family and certain other species eat vegetable food.
Lizards themselves are sought as prey by all sort of carnivorous beasts, birds and reptiles, in avoiding which they must rely mainly on their alertness and agility in dodging or outrunning the foe. Most of them are conspicuously colored, and many exhibit as great gaudiness as do tropical birds, so that this class of animals would seem to have been denied any benefit that might accrue from “concealing coloration” as ordinarily understood One remarkable peculiarity of lacertilian structure, however, is perhaps protective, although the expedient is rather a costly one, namely, the ability of most lizards to part easily with the tail. This is the part of the lizard most likely to be snapped at by a captor, the more so as it is commonly held aloft when its owner runs, and breaking off easily enables the remainder of the lizard to go on running, while the baffled foe contemplates his useless booty. A new tail speedily replaces the lost member, but it is never quite as good as the original one. Some small lizards, when startled, cast off their tails with a jerk before they are touched; on the other hand, the big monitors indulge in no such sacrifice, but utilize their long and strong tails as powerful whip-like weapons of defense.
Reproduction in lizards as a rule is by a small number of eggs laid in damp earth, but a few, as the skinks, bring forth young alive. Lizards are of service to mankind in destroying insects and other vermin, and in the tropics are welcomed in native houses for that reason. The water monitor is a valuable curb on crocodiles, by devouring their eggs and young. Many lizards furnish good human food, especially the larger iguanas, that are a regular part of the aboriginal diet in South America, as are other lizards among the Blackfellows of Australia. Certain species also make amusing pets. Consult, besides general works, Gadow, ‘Amphibia and Reptiles’ (New York 1901); Pycraft, ‘Story of Reptile Life’ (London 1905); Ditmars, ‘The Reptile Book’ (New York 1907); Boulenger, ‘Reptiles and Batrachians’ (London 1914).
AMERICAN LIZARDS
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| 1 Uraniscodon umbra | 2 Teju or Tupinambia |
| 3 Surinam ameiva | 4 Gila Monster or Heloderma |
OLD WORLD LIZARDS
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| 1 Skink | 4 Zonurus cordylus |
| 2 Lacerta agilis | 5 Agama colonorum |
| 3 Nile Monitor or Varanus | 6 Gila Monster or Heloderma |