166 WATER REPTILES OF THE PAST AND PRESENT 



zygosphenal articulations of the vertebrae, wanting in other forms, 

 as also by the structure of their paddles. They had a relatively 

 long body and short tail, the tail having a more pronounced distal 

 expansion than in the case of other forms, and the eyes looking 

 laterally, not at all upward. The feet, as shown in Fig. 74, were 

 broad and short, with most of the wrist and ankle bones well 

 ossified, and with but few extra bones in the digits. Tylosaurus 

 (Fig. 79), on the other hand, had a more slender skull, the nostrils 

 were situated farther back from the tip of the snout, the tail was 

 longer and more powerful, and the feet were very highly specialized 

 (Fig. 75). The wrist and the ankle were almost wholly carti- 

 laginous, the fifth finger and fifth toe were much longer, and the 

 number of phalanges was greatly increased. Moreover, the bones 

 of the skeleton are more spongy, the joints are more cartilaginous, 

 and the ears were better protected by a heavy coat of cartilage. 

 In most of these respects the genus Platecar pus was intermediate 

 between Clidastes and Tylosaurus (Fig. 76). 



Like nearly all other lizards, the mosasaurs had a pineal open- 

 ing in the skull, but it is not at all probable that they possessed a 

 functional pineal eye. 



Many and varied have been the opinions of scientific men 

 regarding the relationships of these animals, as has been intimated. 

 They were thought to be a kind of whale or breathing fish by 

 Peter Camper; crocodiles, by St. Fond; and aquatic lizards, by 

 Adrian Camper and Cuvier. The late Professor Cope thought 

 they were more nearly related to the snakes than to the lizards, 

 and that they might even have been the ancestral stock from which 

 the snakes have descended. Because of this belief he gave to them 

 the name Pythonomorpha, meaning python-like, and this name, 

 really the first ever applied to them, is yet often used instead 

 of Mosasauria. A more complete knowledge of the mosasaurs, 

 however, and especially the recent discoveries of the semiaquatic 

 connecting links, called the aigialosaurs and described on a pre- 

 ceding page, have set at rest all doubt as to their real affinities. 

 They are real lizards, differing less from the living monitor land 

 lizards than do the monitors from some other land lizards, espe- 

 cially the amphisbaenas and chameleons. And to Adrian Camper 



