vi MARINE REPTILES OR THE OXFORD CLAT. 



pointed snout. Both the shortening of the neck and the elongation of the head 

 seem to show that these reptiles could not merely paddle on the surface of the water, 

 but swim through its depths at considerable speed. The means of propulsion, also, in 

 the Pliosaurs differs somewhat from that of the Elasmosaurs, in which the fore paddle 

 was the largest and most important organ of progression. In the Pliosaurs, on the 

 other hand, the fore paddle, though still large, is the smaller, and the shoulder-girdle 

 is comparatively weak, while the pelvis and hind limb are enlarged and clearly played 

 the chief part in swimming: there is no evidence that the tail bore any fin or took any 

 part in the propulsion of the body in the members of this group. 



Although, from the contents of the stomach of Peloneustes (see Introduction to 

 Part I. p. xvi), it is certain that these animals fed largely on Cephalopods, nevertheless 

 the great size and strength of the teeth in the Pliosaurs generally seem to indicate 

 that probably larger and more powerful animals were caught and killed by them. It 

 is also likely that many of the deeply scored grooves often seen on bones from this 

 horizon, were caused by the teeth of these animals while feeding on the carcases, and 

 this use of the teeth may account for the considerable degree of wear often exhibited by 

 the tooth-crowns, e.g., in the teeth of Peloneustes cvansi, shown in text-fig. 28 (p. 73 

 of the present volume). Of course, in many cases the tooth-marks may have been 

 caused by some of the numerous Crocodiles. 



All the members of the Sauropterygia described in this Catalogue are too highly 

 specialised for an aquatic life to supply any valuable information as to the early history 

 and relationships of the order, but in the Trias there occur several genera which are of 

 considerable importance from this point of view. The earliest remains are from the 

 Lower Trias, but it is in the Middle Trias (Muschelkalk) that they become abundant 

 and sufficiently well-preserved to establish any conclusions. The best-known genus 

 is Kothosaurus, of which the osteology of several species has been fairly completely 

 worked out; some traces of a terrestrial ancestry are shown, e.g., in the comparative 

 elongation of the propodial bones, but this animal had already attained a large size and 

 was mainly, if not entirely, aquatic in its habits, so that it is of less importance from a 

 phylogenetic point of view than the smaller forms, such as Lariosaurus and Neustico- 

 sanrus. These are small lizard-like reptiles, which were probably amphibious, 

 but certainly were capable of progression on land. A nearly complete skeleton of 



