RELA TIONS AND HABITS OF MOSASA URS 49 



them in almost every stage of adolescence, and the embryos 

 have been discovered in Europe. Furthermore, I have often 

 sought in vain for the remains of young mosasaurs in the stom- 

 ach contents of different animals in the Kansas Cretaceous, and 

 in the bone-beds, which rarely occur in that formation. Under 

 such apparently favorable circumstances as are presented by the 

 chalk deposits of western Kansas, the seemingly entire absence 

 of all remains of young mosasaurs is inexplicable. Half-grown 

 forms do occur, but none that are very young. As I have pre- 

 viously remarked, it is certain that all mosasaurs did not die of 

 old age. Indeed, the many hyperostosial mutilations of ante- 

 mortem origin indicate only too well the fierce struggles the 

 mosasaurs had with the carnivorous enemies of their own and 

 other kinds. 



If the mosasaurs were exclusively marine animals, it would 

 seem almost certain that they were not viviparous, as were the 

 ichthyosaurs, and probably also the plesiosaurs, and as are some 

 modern lizards. As Fraas has remarked concerning the European 

 ichthyosaurs, if one searches carefully, he will find in many Kan- 

 sas specimens the remains of the skin and stomach contents, 

 but never has there been found anything which has the faintest 

 suggestion of mosasaur embryos. No aquatic reptiles of the pres- 

 ent time lay their eggs in the water. The sea snakes are vivipa- 

 rous, or at least all available information concerning them gives 

 viviparous habits. The sea turtles and the crocodiles lay their 

 eggs upon the beaches, the latter guarding their nests and young. 

 Doubtless the crocodiles of the past had the same beach-laying 

 habits, suggesting that they were never inhabitants of the 

 open oceans. The mosasaurs must have been practically helpless 

 upon land ; still it is not impossible that they may have frequented 

 the beaches for the deposition of their eggs, though it is highly 

 improbable that they gave any attention or care to either their 

 eggs or their young. That the eggs of the mosasaurs were more 

 numerous than are those of the terrestrial lizards of the present 

 time is not to be supposed. The waters in which the mosasaurs 

 flourished swarmed with highly predaceous fishes, sharks, and 

 plesiosaurs, to say nothing of the hordes of their own kind; and. 



