174 WATER REPTILES OF THE PAST AND PRESENT 



like those of the mosasaurs, as will be seen by comparing the figure 

 on p. 157. The humerus is a little more elongated than that of 

 the mosasaurs, more nearly like the mosasaurian femur. The 

 shoulder-blade and the coracoid are imperfectly ossified, as is seen 

 from the figure — another characteristic of aquatic life. What the 

 fingers and toes were like cannot be said; probably, they were 

 bound together by membrane, forming 

 swimming paddles similar to those of the 

 mosasaurs. Some of the bones referred to 

 the pelvis are known, but it is not known 

 whether they are united to the spinal 

 column by a sacrum, as in land animals. 

 Nor is anything certainly known of the 

 hind leg or much of the tail. Since the 

 front legs show marked aquatic adapta- 

 tions, it is altogether certain that the hind 

 legs will be found to be modified more or 

 less, though not so much modified as the 

 front legs, because, as we have seen, the 

 front legs are always more specialized in 

 aquatic animals than the hind ones, even 

 as the hind legs are more speciaUzed than 

 the front ones in land animals. Possibly the hind legs will be 

 found to be more like those of the Thalattosuchia, as shown on 

 p. 212, that is, partly terrestrial in character. Doubtless the tail 

 was long and flattened, possibly with a terminal fin-like dilation, 

 though this is less probable. 



As rega,rds the habits and food of the thalattosaurs, no better 

 summary can be given than that of Professor Merriam, in his own 

 words : 



The remains of thalattosaurs are known only in purely marine deposits 

 containing little or no material of terrestrial origin. They are associated with 

 a fauna consisting of numerous forms, both vertebrate and invertebrate, 

 which are not known to have existed away from marine areas. In the struc- 

 ture of the skeleton we find the abbreviated and broadened proximal segments 

 of the limbs, the slender snout with prehensile terminal teeth, and the median 

 superior nostrils, indicating a purely aquatic type. There can scarcely be 

 room for doubt that the thalattosaurs as a group were typical marine forms. 



Fig. 84. — Thalattosaurus: 

 bones of front extremity: 

 s, scapula; c, coracoid; h, 

 humerus; r, radius; u, ulna. 

 (After Merriam.) 



