LIZARD, a subclass of reptiles, whose
anatomical features and classification have been
described under . 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.