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HISTORICAL GEOLOGY 



This was accomplished by a hinge in each half of the lower jaw (Fig. 

 516) which permitted it to bow outward when open. The articulation 

 of the jaw with the skull also assisted in this process. The limbs were 



Fig. 516. 



Skeleton of a Cretaceous mosasaur about sixteen feet long. 

 (After Williston.) 



not as greatly modified as in the ichthyosaurs, but were completely 

 paddle-like and resembled those of the whale. The great speed with 

 which it could be propelled by its tail made the catching of its fish 

 food an easy matter. Mosasaurs were descended from land animals 

 and may have sprung from the same stock as modern reptiles. 

 They were not well established until the Upper Cretaceous, in which 

 period they rapidly diverged and swarmed the Atlantic and Gulf 



FlG. 517. — Restoration of a Cretaceous mosasaur. (Painted by C. R. Knight 

 under the direction of Prof. H. F. Osborn. (Copyright, American Museum of Natural 

 History.) 



coasts and the interior seas. They had a wide distribution, being 

 found in North and South America, Europe, and as far south as 

 New Zealand. They disappeared with the Mesozoic, after having 

 h<id a comparatively short life. 



