CHAPTER XV 

 CROCODILIA 



The order of reptiles to which the name Crocodilia is technically 

 applied comprises less than twenty-five living species, popularly 

 known as crocodiles, alligators, caimans, and gavials. They are 

 often of great size, ugly and repulsive in appearance, cruel and 

 vicious in habit, wholly carnivorous, and denizens, almost exclu- 

 sively, of fresh-water lakes or rivers in tropical and subtropical 

 regions; a few only venture into the sea near the shores. They are 

 all excellent and powerful swimmers, but are by no means exclu- 

 sively aquatic in habit, many of them spending a large part of the 

 time on the shores; and they invariably seek the land for the 

 deposition and hatching of their eggs. In size they are the largest 

 of living reptiles, some of the existing species reaching a length of 

 twenty-five feet, while some extinct species were probably fully 

 twice that length. 



The geological history of the crocodiles is a very ancient one, 

 reaching back at least as far as the early Jurassic and probably to 

 the Triassic. The culmination of the order, at least so far as size, 

 variety, and numbers are concerned, was doubtless before the close 

 of the Mesozoic. The early crocodiles, however, were of a more 

 generalized structure in some respects, though specialized in others, 

 because of which naturalists in the past have usually divided the 

 order into three or four chief subdivisions, 6r suborders, two of 

 which, the Mesosuchia and the Thalattosuchia, became extinct 

 before or during Cretaceous time. The third suborder, the Para- 

 suchia of many textbooks, has now been unanimously separated 

 by paleontologists from the Crocodilia as an independent order. 

 The fourth suborder of the textbooks, the Eusuchia, a word meaning 

 true crocodiles, appeared in geological history, so far as we yet know, 

 shortly before the extinction of the Mesosuchia, and is best known 

 from the forms now living, all of which belong to it. Although the 



194 



