CENOZOIC ERA: AGE OF MAMMALS 



625 



climate not unlike that of Florida to-day, and a country similar to 

 the bayou region of the Mississippi delta. The rivers of this time 

 swarmed with turtles, but the presence of land tortoises, some of 

 which were three feet long, indicates that these swampy areas were 

 bordered by extensive stretches of dry land. Numerous land tor- 

 toises in the Oligocene deposits of the Great Plains show that dry- 

 land conditions were widespread. Since spiny lizards are largely 

 confined to-day to arid regions, the presence of numerous lizards 

 (Glyptosaurus) with skulls covered with spiny, bony plates is in- 

 dicative of dry conditions in Montana during a portion, at least, of 

 the Oligocene. 



REFERENCES FOR REPTILES AND AMPHIBIANS 



Cunningham, J. T., — Reptiles, Amphibians, and Fishes. 

 Osborn, H. F., — Age of Mammals, pp. 208-209. 



Fishes. — The fish of the Tertiary were abundant and very similar 

 to those of the present seas. Ganoids were represented by a few 

 species, and teleosts 

 were very much as 

 at present, both in 

 numbers and in ap- 

 pearance. The most 

 noted deposit of 

 fossil fish in America 

 is that of the Green 

 River (Eocene) 

 shales of Wyoming, 

 where thousands of 

 beautifully pre- 

 served specimens 

 have been quarried, 

 examples of which 

 can be seen in almost 

 any museum. The 

 great number of sharks' teeth (Fig. 555 A-D) in the Tertiary deposits 

 of the Atlantic Coastal Plain of North America and elsewhere show 

 that sharks were very abundant in this period. Some of them must 

 have been of great size, judging from the teeth some of which are six 

 and one half inches long and six inches broad. A close living relative, 

 the great white shark, has teeth one and one fourth inches long. If 



Fig. 555. — Tertiary shark teeth: A, Odontaspis cus- 

 pidata; B, Carcharodon megalodon; C, Hemipristis serra; 

 D, Odontaspis elegans. (After Maryland Geol. Surv.) 



