SQUAMATA 163 



Even small fishes could not possibly have been swallowed by 

 the mosasaurs in any other way than head first, since the back- 

 wardly projecting, and often long, spines would have rendered 

 any other procedure impossible. Even after the head had entered 

 the ^llet, deglutition could have been effectively completed only 

 by the aid of some mechanism whereby the fish could have been 

 pulled or pushed back into the constricting fauces. .The strong 

 teeth of the upper jaws and palate held firmly the struggHng prey, 

 while the loosely united jaws, bending laterally at the joint back 

 of the middle, either alternately, or more probably in unison, 

 steadily forced it far enough back to be seized by the muscles 

 of the fauces. 



The shape of the mosasaurs, though slender, does not suggest 

 extraordinary speed in the water; doubtless most of the fishes 

 that lived in the seas with them could swim faster than they. 

 Their prey was captured, for the most part at least, by sudden 

 and quick lateral movements, for which their powerful and flexible 

 paddles a4mirably adapted them. 



It is .a rather remarkable fact that, among the thousands of 

 specimens of mosasaurs which have been collected during the past 

 forty years in both Europe and North America, there never has 

 been found one of a very young animal. Of almost all other 

 animals occuring abundantly as fossils some specimens are sure 

 to be discovered of young and even embryonic individuals. It 

 is quite certain that all such voracious monsters as were the mosa- 

 saurs did not die of old age. Some specimens, it is true, have been 

 found that were evidently not full-grown animals, but the observed 

 differences in the size of the fossil bones are not great. All are of 

 adult or nearly adult animals. If the mosasaurs were oviparous, 

 as were the idithyosaurs, and probably the plesiosaurs, and as 

 are some living land lizards, the apparently entire absence of 

 embryonic bones associated with often nearly complete skeletons 

 of the mosasaurs is inexplicable; certainly some mosasaurs must 

 have died a short time before the birth of their young. But 

 embryos have never been discovered, though numerous skeletons 

 inclosing fossilized stomach contents have been found. From 

 this fact it would seem very probable that the mosasaurs were 



