SQUAMATA 161 



been observed among the fossilized stomach contents, and it is 

 quite certain that the food of these creatures must have been com- 

 posed chiefly of fishes, though of course it is not improbable that 

 other small vertebrates, birds, pterodactyls, the young of plesiosaurs, 

 and possibly small mammals, may occasionally have formed a 

 part of their diet. That the mosasaurs were very pugnacious 

 in life is conclusively proved by the many mutilations of their 

 bones that have been observed, mutilations received during life 

 and partly or wholly healed at the time of death. Bones of all 

 vertebrates are repaired after injury by the growth of more or less 

 spongy osseous material about the injured part, forming a sort 

 of natural splint. This material is more or less entirely removed 

 by absorption when it is no longer required for the support of the 

 broken ends. Many such injured bones of the mosasaurs have 

 been found; sometimes the bones of the hands and feet have grown 

 together, and not infrequently the vertebrae have been found 

 united by these osseous splints; occasionally even the skull itself, 

 especially the jaws, attest extensive ante-mortem injuries. In a 

 single instance the writer has observed the loss of a part of the tail, 

 where it probably had been bitten off. It may be mentioned, how- 

 ever, that the bones of the tail had no such "breaking points" in 

 the mosasaurs as have those of many land lizards, whereby a part 

 or all may be lost as a result of even a trivial injury, and then 

 regrown. Such a condition in an organ relied upon entirely for 

 propulsion would have been immediately fatal to the existence of 

 the mosasaurs. The large jaws and teeth are in themselves suffi- 

 cient evidence of the fiercely carnivorous propensities of the mosa- 

 saurs. The constant renewal of the sharply pointed teeth, thereby 

 preventing deterioration by use or accident, preserved, even in the 

 oldest animals, the effectiveness of the youthful structure. 



We may now understand how the mosasaurs seized and swal- 

 lowed their prey. Living constantly in the water, away from all 

 firm objects, with small, short limbs quite incapable of holding 

 struggling prey, and the body not sufficiently serpentine to hold 

 it in its folds after the manner of snakes, the mosasaurs would have 

 found it difficult or impossible to swallow fishes of even moderate 

 size, were their jaws of the same construction as are those of the 



