90 WATER REPTILES OF THE PAST AND PRESENT 



complete skeletons, however, preserved as they were found in the 

 matrix, are shown in various museums. 



With these principal facts regarding the structure, size, and 

 external form of these animals we may venture to draw certain 

 conclusions, or at least to offer certain conjectures as to their habits 

 in Hfe. 



Because of the rigid structure of the jaws, united in front and 

 incapable of any lateral movement posteriorly, quite as are the 

 jaws of crocodiles, we are sure that prey of any considerable size 

 could not have been swallowed whole. The crocodiles tear away 

 portions of the flesh of their victims by quick, powerful jerks, and 

 it is very probable that the flat-headed plesiosaurs tore their food 

 apart in the same manner. In these kinds the teeth are much 

 larger and more irregular in size than are those of the long-snouted 

 plesiosaurd, and their use was certainly as much for tearing as 

 for seizing. There are the same differences between the size of 

 the head and the size of the teeth among the various plesiosaurs 

 that there are among the modern crocodiles and gavials. While 

 the crocodiles seize and destroy even larger prey, drowning and 

 tearing their victims to pieces, the gavials are more exclusively 

 fish-eating, for which their small, sharp, and more numerous teeth 

 especially fit them. Their food, of small size, is swallowed entire, 

 and they are comparatively harmless, so far as animals of consid- 

 erable size are concerned. 



The long neck, the thickset body, and short, stout tail are not 

 at all what we should expect to find in quick-swimming animals. 

 We may therefore assume that the motions of the plesiosaurs 

 through the water were more turtle-like than fish-hke. The tail, 

 even though provided with a terminal, fin-like dilatation, was of 

 little use in the propulsion of the body, since the range of its move- 

 ments was restricted; it possibly served in a measure as a steering 

 organ, a rudder. The large, freely movable paddles must have 

 been effective organs of locomotion, and this function accounts for 

 the relatively large size of the posterior pair, and the firm union of 

 the pelvis with the vertebral column through the sacrum. With 

 the hind limbs used as oar-hke organs, a firmer union with the 

 skeleton was required than the soft yielding flesh would permit. 



