Water Reptiles of the Past and Present

by Samuel Wendell Williston

There is much difference of opinion among naturalists as to the proper classification of the different groups of this order of reptiles. Usually it is divided into four suborders, the Lacertilia or lizards; the Dolichosauria or long-necked lizards of the past; the Mosasauria, or extinct swimming lizards; and the Serpentes or Ophidia, the snakes. It matters very little which classification one accepts so long as it is remembered that the first three groups are closely related to each other.

LIZARDS

Popularly a lizard is any four-legged reptile covered with scales, but such a definition is not strictly correct, since some lizards are legless and some other four-legged reptiles are covered with horny scales, notably the tuatera or Sphenodon of New Zealand, a reptile long classed with lizards, but now known to belong to quite a different order. Bearing in mind those characters given as characters of the order, it will be necessary to mention only those distinguishing the lizards from the snakes.

Fig. 65.—Iguana.
(By permission of the New York Zoölogical Society)

It is true that the great majority of lizards have four legs, while the snakes are always functionally legless, but there are some lizards, like the glass snakes and the amphisbaenas, or slow lizards, which are quite legless and there are some snakes which have small but functionless hind legs. As usual, more important differences are found in the skull. The brain-case in all snakes is surrounded on all sides by bone, for the better protection of the brain, with the head resting quite prone on the ground. The brain of the lizards, for the most part, is protected on the sides and in front by a simple membrane. Nearly all lizards have movable eyelids, while snakes do not; snakes have a single lung, and a protrusible tongue, which very few lizards possess; and the lower jaws in front are united in the snakes by a ligament only. Notwithstanding these differences, the snakes and lizards are closely related animals, and must have come from a common ancestry; among all reptiles the known geological history of the snakes is shortest.

Lizards, on the other hand, have a very high antiquity, beginning, as we now know, at least as long ago as early Triassic times. They still have many primitive characters in their structure and are the least advanced type of reptiles now living, with the exception of the tuatera. Their remains are seldom found in the rocks, probably because they have always been so strictly terrestrial in habit, for the most part seldom frequenting even the vicinity of the water. The true lizards now living number about eighteen hundred kinds, classified into about twenty families, divided among four chief groups, of which the chameleons, the amphisbaenas, our common lizards, and the monitors are representatives.

Most living lizards are inhabitants of warm climates, though some extend rather far north in the temperate zone. With the exception of New Zealand, and the polar and subpolar regions, lizards are found in all parts of the world. The great majority live only in high and dry places, though some are denizens of low and marshy places, a few even not being averse to the water. They are, for the most part, spry in their movements, some little ones scarcely six inches in length taxing a vigorous man’s speed to capture; and many are expert climbers of cliffs, trees, and even the ceilings of residences. Some, the remarkable little flying dragons of Ceylon, have an extraordinary development of the skin on the sides of the body, supported by the expanded ribs, forming a sort of parachute whereby the creatures can sail considerable distances through the air. Nearly all are carnivorous, feeding upon small mammals, birds, other reptiles, frogs, and insects; a few only are herbivorous, such as the iguanas, which are often used for human food. Nearly all lizards are oviparous, laying from two to thirty eggs. In size the great majority are small, less than a foot in length; but some, such as the monitors and iguanas, reach a length of from four to six feet, or even more, and certain extinct monitors of India are known to have attained a length of thirty feet. They are, for the most part, slender, graceful, prettily marked, and quite inoffensive creatures. A few are short, flat, or stumpy in shape, such as the so-called horned toad. One or two species only, the “Gila monsters,” are reputed to be venomous.

Fig. 66.—Amblyrhynchus cristatus, the Galapagos sea-lizard.
(From Brehm)