The second family, the Tomistomidae, or long-snouted crocodiles, comprises but two living species, both restricted at the present time to Borneo. These crocodiles have a moderately slender snout, because of which they are sometimes called gavials, though it is not nearly so slender as that of the true Gangetic gavial. This family is probably older than either of the other living ones, and is the only one known with certainty to have lived during much of the Cretaceous times, several species of considerable size having been found in New Jersey and Europe. Their feet are better webbed than are those of the true crocodiles and alligators, the front feet partly, the hind feet wholly so. In general structure they seem to be the most primitive of the living Crocodilia, and may have been the ancestors of all modern forms.
Fig. 105.—Gavial.
(By permission of the New York Zoological Society)
The third family, the Gavialidae, also comprises but two living species, both restricted in habitat to the rivers of India. Of these the famed gavial of the Ganges is the better known and the more highly specialized. The skull of this species has an exceedingly long and slender snout; the teeth are numerous, small, and slender; and the feet are more fully webbed than are those of other members of the order. In habits the gavials are more distinctly aquatic than are the crocodiles and alligators. They feed almost exclusively upon small fishes, for the seizure and retention of which their small and sharply pointed teeth are admirably adapted. The hind feet are relatively long, a character that will be better understood when comparison is made with those of the Thalattosuchia. Although attaining a large size, fully twenty-five feet in length, they are comparatively harmless animals, never attacking human beings or other large animals, as do some of the crocodiles proper. The gavials have lived a long time in the Indian regions, the Gangetic gavial itself having been found in deposits of Pleiocene age, perhaps the oldest known of all living species of air-breathing vertebrates. Some of the extinct gavials of the same region attained a length of nearly or quite fifty feet, possibly the longest, if not the largest, of all swimming reptiles of ancient or modern times. Extinct gavials have been reported from South America, but are not yet fully known.
While the fish-eating gavials swallow their prey whole, the crocodiles, caimans, and alligators prey upon all living animals that come within their reach, whether large or small, and they will often leave the water to seize their intended victims, such as pigs, sheep, birds, or even human beings. Their teeth, as has been already stated, are much larger, longer, and more irregular in size than those of the gavials. Their victims are often drawn under the water and drowned, the peculiar posterior position of the internal nostrils permitting the animals to breathe with the mouth and to firmly hold their prey under water, while the extremity of the snout and the external nostrils are above the surface.
As the firm, unyielding bony palate, the fixed position and articulation of the lower jaws, and their rigid attachment to each other in front do not permit creatures of large size to enter the gullet whole, the crocodiles and alligators must tear their food to pieces, which they do by quick, strong jerks from side to side, aided by the powerful tail; or they may twist off a limb or some other part of their victims by a rapid rotation of the whole body, two assisting in this operation, rotating in opposite directions.
Living crocodiles lay from twenty to sixty eggs, according to the species; these eggs are sometimes the size of a goose egg, and are covered with a hard shell. They are laid either in a deep excavation in the sand and covered over by the parent; or under leaves and straw. The female remains on guard until the eggs are hatched, of which she is apprized, it is said, by a peculiar noise uttered by the partly imprisoned young. She thereupon reopens the nest, and guides her liberated infants to the water, where she leaves them to their fate. Whether this remarkable habit is one that has been acquired in recent times or not is uncertain, but because it has been observed in a number of unrelated forms, it is probable that the instinct is of long inheritance, and may account for certain peculiarities of structure in some of the ancient members of the order. Doubtless the habit arose because of the unprotected places in which the eggs are necessarily laid on the shores and beaches, and because the eggs are comparatively so few in number. The sea-turtles likewise lay their eggs in hollows scooped out of the sand of the beaches, but the parents give no further care to their eggs, nor to their newly hatched offspring, a neglect which is compensated for by the much larger number of eggs they lay, because of which the chances are much greater that a few will survive the more numerous vicissitudes to which the eggs and young turtles are exposed.
ANCIENT CROCODILES,
MESOSUCHIA
The name Mesosuchia, meaning “middle crocodiles,” by which the ancient members of the Crocodilia have generally been known, was given by Huxley in the belief that they were intermediate between the “true” or modern crocodiles and an ancient group which he united with the order under the name “Parasuchia.” A fuller and better knowledge of the members of this last group has proved very conclusively that they are really less allied to the crocodiles than are some other orders of reptiles, the dinosaurs for instance, and should be properly classed by themselves as a distinct order. And, more recently, it has also become quite apparent that the old crocodiles should not be separated so widely from the modern ones as Huxley proposed; that the differences distinguishing them from the recent members of the order are really not of more than family importance. We thus have left but two chief divisions of the Crocodilia, the Eusuchia and Thalattosuchia; and the latter group even, by some authors, perhaps rightly, are included under the true crocodiles as a family only.
