32 



CROCODILES. 



as Rhamphosuehus, which attained a length of some 50 or 60 feet, and had teeth as 

 large as those of the biggest crocodile ; its upper teeth biting on the outer side of 

 the lower ones, instead of interlocking with them, as in the living form. 



The Earlier Crocodiles. 



As already mentioned, all the existing crocodiles, together with the species 

 from the Tertiary formations, constitute a single family, characterised by the 

 vertebra? having a ball in front and a cup behind, and by the internal nostrils 

 being situated at the hinder end of the skull ; as well as by the bony plates of the 

 back being arranged in at least four longitudinal rows. Although a few species 

 found in the topmost beds of the underlying Secondary formations approximate in 

 some respects to the foregoing, the majority of the crocodiles from rocks as old or 

 older than the Chalk differ very considerably from the existing types. In the first 

 place, the bodies of their vertebras articulate with one another by slightly hollowed 

 surfaces at both ends ; while, owing to the want of union between the hindmost 

 bones of the palate beneath the nasal passages, the internal apertures of the nostrils 

 are situated nearly in the middle of the skull. Then again, when a bony armour 

 is present, the plates on the back are arranged in only two longitudinal rows ; 

 while those on the lower surface of the body form two distinct shields. It is 

 remarkable that among these extinct crocodiles some are met with having broad 

 and short snouts like the modern alligators, while others have long- and narrow 

 snouts like the garials. In the Wealden and Purbeck rocks, underlying the Chalk, 

 some of these crocodiles, such as the short-snouted Swanage crocodile (Ooniopholis), 

 resembled living types in having the socket of the eye communicating freely with 

 the lower temporal fossa, although they were distinguished by the plates of the 

 back articulating together by means of a peg-and-socket arrangement. In still 

 older formations, such as the Lower Oolites and Lias, there were, however, many 

 long-snouted crocodiles, such as the steneosaurs (Steneosaurus) and pelagosaurs 

 (Pelagosauras), in which the socket of the eye is divided from the lower temporal 

 fossa by a bony bar, as shown in the figure on p. 13. Moreover, in these forms the 

 upper temporal fossa (T in the figure cited) was larger than the socket of the eye ; 

 whereas in all living forms the former is much the smaller of the two, and may even 

 be obliterated. Another group of crocodiles, — the metriorhynchs (Metriorhynchus), 

 — of the Oxford and Kimeridge Clays, were remarkable in having no bony armour 

 at all, in which respect they were more specialised than any of their living cousins. 

 In general, however, the earlier extinct crocodiles, as will be gathered from the 

 foregoing remarks, were decidedly of a less specialised type than those of the 

 present day ; and as a gradual transition can be traced in these respects from the 

 oldest to the most recent, the group affords a very interesting instance of progressive 

 evolution. In the very oldest of the secondary rocks, namely, the Trias, there occur, 

 both in Europe and India, certain very remarkable long-snouted reptiles, known as 

 Parasuchians, which appear in some respects intermediate between crocodiles and 

 tuateras. Thus, while they resembled the former in the nature of their teeth, bony 

 armour, ribs, and vertebrae, they approximated to the latter in the structure of the 

 skull, abdominal ribs, and probably of the collar-bones and interclavicle. 



