TEA LA TTOSA URIA 1 7 5 



The larger and more specialized species comprised in the genus Thalattosaurus 

 were strictly natatory. They may have visited the shore, but, like the plesio- 

 saurs, were better fitted for swimming than for crawling. Of the smaller 

 Nectosaurus we unfortunately do not know the limbs. They may have been 

 considerably less specialized, and the animal to a correspondingly greater degree 

 a shore-dweller. Nectosaurus is, however, found in the same deposits with 

 other forms and appears to be as common as the others; so that it is safe to 

 consider it as having passed the greater part of its life away from the shore. 



From what we know of the vertebral column of Thalattosaurus it appears 

 that the animal had a relatively short neck and a long dorsal region, the pro- 

 portions being nearly those in the vertebral column of some mosasaurs. Only 

 the anterior portion of the caudal region is known. The slender, rounded neural 

 spines with well-developed articulating processes seen here are not such as 

 commonly appear in forms with a highly specialized sculling tail, and it is 

 hardly probable that a caudal fin of large size was developed. 



The anterior limbs evidently formed paddles of moderate size. The 

 posterior pair may have been larger, in compensation for lack of a strong scull- 

 ing tail. It is, however, possible, that as in Geosaurus (of the thalattosuchian 

 crocodiles) the hind limbs were not typically natatory, and the distal end of the 

 tail was vertically expanded. 



No specimens have yet been found which are well enough preserved to 

 show any remains of the stomach contents, and we have no definite evidence 

 concerning the food of the thalattosaurs, more than is furnished by the general 

 structure of the animal. The character of the paddles, the form of the skull, 

 and the presence of slender prehensile teeth in the terminal portions of the 

 jaws would indicate that they fed in part upon some swiftly moving prey 

 which was caught by a quick snap of the jaws, deglutition being assisted by the 

 curved teeth of the pterygoids. The heavy vomerine and posterior mandibular 

 teeth may have been used for crushing the light shells of ammonites, which 

 existed in vast numbers in the same seas. 



