TERTIARY ANIMALS. 



537 



is well to note also that the American Continent, as shown by the 

 uniqueness of its mammalian fauna was still completely isolated. 



8. Mauvaises Terres — Niobrara Basin— Loup Fork Beds— Pliocene. 

 — In nearly the same locality overlying the last, but extending farther 

 south, occur lake-deposits of the Pliocene times, full of mammalian re- 

 mains, but again wholly different in species. Among Ungulates there 

 was a Rhinoceros, as big as the Indian species ; an Elephant (E. Ameri- 

 canus), the same which lived in the Qua- 

 ternary, bigger than any now living ; a Mas- 

 todon, but smaller than the great Mastodon 

 of the Quaternary ; a large number of the 

 horse family and several of the camel fami- 

 ly, besides many other families of Ungu- 

 lates, Carnivores, Eodents, etc. Both the 

 horse and the camel family were more nu- 

 merously represented at that time in America 

 than in the Eastern Continent. In fact, it 

 is not at all improbable that they originated 

 here, and emigrated to the other continent. 



From the presence of Elephants, Mastodons, Rhinoceros, Camels, and 

 Horses on both continents, we conclude that the hvo continents were 

 probably connected in Pliocene times. 



Among the horse family found here, the most interesting, as show- 

 ing the gradual approach toward the modern horse, are the Protohippus 

 and the Pliohippus. These were larger than the Miocene horses, being 

 about the size of the ass. The former was three-toed, but the two side- 

 toes were smaller and shorter and scarcely functional, unless on marshy 

 ground ; the latter had already lost the side-toes, and was almost but 

 not quite a perfect horse. 



We see here for the first time existing genera. Elephas, Canis, and 

 in the higher beds Equus begin to appear, but not yet existing species, 



TERTIARY 



Rhinoceros. 



Elephant. 



Mastodon. 



Three of the Camel family. 



Five of the Horse " 



Oeodon. 



Deer. 



Fox. 



Wolf. 



Tiger. 



Beaver. 



Porcupine. 



Fig. 917.— The Successive Appearance and Increasing Percentage of Existing Orders, Families, 

 Genera, and Species of Mammals. 



for these do not appear until the Quaternary. The successive appear- 

 ance and increasing percentage of existing orders, families, genera, and 

 species of mammals, is shown in a very general way in the accompany- 

 ing diagram. 



