438 



MESOZOIC ERA— AGE OF REPTILES, 



many extinct reptiles, apparently for adjusting the eye to different dis- 

 tances. The tail was long, and probably provided terminally with a 

 vertical, fin-like expansion, unsupported by rays (Owen). In addition 

 to the powerful fin-tipped tail, the locomotive organs were four short 

 stout paddles, composed of numerous closely-united bones, but without 

 distinct toes. These paddles were surrounded by an expanded, ray- 

 supported web (Fig. 687), which greatly increased their surface, and 

 therefore their efficiency as swimming-organs (Lyell). The bodies of the 

 vertebrae were not united by ball-and-socket joint, as in most living rep- 

 tiles, but were bi-concave (amphiccelous), like those of fishes (Fig. 685). 



That the habits of 

 the creature were preda- 

 tory and voracious is 

 sufficiently attested by 

 the teeth. It is further 

 proved by the contents 

 of the stomach, which 

 are sometimes partly 

 preserved. These con- 

 sist largely of fish- scales. 

 From the descrip- 



-Paddle- Web of an Ichthyosaurus, ti(m giyen aboye ifc j g 



plain that the Ichthyosaurus combined in a remarkable degree the 

 characters of saurian reptiles with those of fishes. The vertically-ex- 

 panded tail-tip, the paddles, with surrounding ray-supported web, and 

 the bi-concave vertebral bodies, are all decided fish 

 characters. In most other respects it was reptilian. 

 This combination is expressed in the name. 



The Plesiosaurus (allied to a lizard) was a less 

 heavy and powerful animal than the last. It was re- 



Fig. 687 



Fig. 688.— a, Head of a Pliosaurus, greatly reduced; b, Tooth of the same, natural size. 



markable for its short, stout, almost turtle-shaped body; its long, 

 snake-like neck, consisting of twenty to forty vertebrae ; its small head ; 

 its short tail, unadapted for powerful propulsion; its long and powerful 

 paddles, which were its sole swimming-organs ; and its bi-concave ver- 



