266 HISTORICAL GEOLOGY 



or darting them to the bottom after their prey, which consisted 

 chiefly of Fish" (W. B. Scott). Plesiosaurs ranged through the 

 whole Mesozoic. 



Mosasaurs were literal "sea-serpents" or carnivorous marine 

 Reptiles which often reached a length of from 40 to 75 feet (Fig. 

 167). Though now wholly extinct, they were closely related to 

 Snakes and Lizards in structure. The four limbs were converted 



Fig. 166 



A restored Plesiosaur, Plesiosaurus dolichodeirus, of the Enaliosaur 

 division of Mesozoic Reptiles. Maximum length 40 to 50 feet. 

 (From Le Conte's "Geology," courtesy of D. Appleton and Com- 

 pany.) 



into short, stout, swimming paddles, and their jaws were set with 

 sharp teeth. The relatively smaller head, long, slender body, and 

 different tail structure distinguish the Mosasaurs from the Ichthyo- 

 saurs, as a comparison of the accompanying pictures will show. 

 Mosasaurs existed during the latter portion only of the Mesozoic. 



Dinosaurs. — These Mesozoic Reptiles comprised a great 

 variety of forms both as regards shape and size. Only five of the 

 more common and characteristic types have been selected for 

 description. 



The Sauropods were the largest of all Mesozoic Reptiles, and 

 in fact thejr included the largest animals which ever trod the earth. 

 Well-preserved specimens are known whose lengths are from 75 to 

 90 feet, and recently one has been discovered in Utah which it is 



