THE CRETACEOUS PERIOD 263 



Mammals. — As in the earlier Mesozoic periods, the Cretaceous 

 Mammals were small, primitive forms which still occupied a very 

 subordinate position among the animals of the time. 



Mesozoic Reptiles 



The Mesozoic era has been appropriately called the "Age of 

 Reptiles," since those animals were at once the most character- 

 istic and powerful creatures of the time. So far as known, the first 

 true Reptiles appeared in the Permian. During the Mesozoic 

 they rose to great prominence, both in number of individuals and 

 diversity and size of forms; reached their culmination in the 

 midst of the era; and declined in a most remarkable manner to- 

 ward the close of the era. During the Mesozoic the Reptiles 

 ruled all fields — sea, land, and air. 



"The advance from the Amphibian to the Reptile was a long 

 forward step in the evolution of the Vertebrates. . . . Yet in 

 advancing from the Amphibian to the Reptile the evolution of the 

 Vertebrate was far from finished. The cold-blooded, clumsy and 

 sluggish, small-brained and unintelligent Reptile is as far inferior 

 to the higher Mammals, whose day was still to come, as it is supe- 

 rior to the Amphibian and the Fish" (W. H. Norton). 



The Principal Extinct Mesozoic Reptile Groups 



The following grouping of the more characteristic, extinct 

 Mesozoic Reptiles is not meant to be an exact scientific classi- 



f 1. Ichthyosaur ("Fish-lizard"). 

 1. Enaliosaurs ("Sea-lizards") i 2. Plesiosaur ("Lizard-like"). 



(Swimming Reptiles). * g * | 3. Mosasaur ("Meuse River lizard") 

 [ (Later Mesozoic only). 



1. Sauropod ("Lizard-footed") 

 (Not known from the Triassic). 



2. Stegosaur ("Plated-lizard") 

 (Not known from the Triassic). 



3. Triceratops ("Three-horned face") 

 (Later Mesozoic only). 



4. Theropod ("Beast-footed"). 



5. Ornithopod ("Bird-footed") 

 (Not known from the Triassic). 



3. Pterosaur (" ^Winged-lizards") , L Pterodactyl ("Winged-finger"). 



(Flying Reptiles). e.g. j 2 Ramphorhyncus ("Beaked-snout"). 



2. Dinosaurs ("Terrible-lizards") 

 (Walking Reptiles). e.g. 



