B. S. Lull — The Evolution of the Horse Family. 169 



movement still continuing, the tooth now gradually shortens 

 until in extreme old age it is practically consumed. The total 

 length of the tooth is nicely calculated to meet the needs of a 

 full measure of life. 



The Geological Occurrence of Horses. 



The geological history of the earth is immensely long and it 

 is only very recently, geologically speaking, that the land 

 animals more or less like modern mammals have been evolved. 

 The earth's history begins in the deepest obscurity, the first 





American 

 Formations 



South 

 America 



North America 



Eurasia 



Recent 





Extinct 



Extinct 



Equus (also 

 Africa) 



a 

 a> 



a 

 o 



m 



Equus Beds 



Equus 



Equus 



Equus 





Blanco 

 Palo-Duro 



Equus 

 Hippidion 



Equus 



Equus 



.2 



Loup Fork 





Pliohippus 

 Protohippus 



Neohipparion 

 Merychippns 



Hypohippus 

 Parabippus 



Hipparion 

 Anchitherium 



03 



a 

 © 

 o 



o 







John Day 





Miohippus 

 Mesohippus 







Anchitherium 



o 

 o 



O 



White Biver 









Uinta 





Epihippus 



Orohippus 

 Helohippus 





05 



Bridget 







a 



o 



o 



Wind Biver 





Protorohippus 

 Eohippus 





H 



Wasatch 





Eohippus 

 Hyracotherium 





Basal 



Eocene 





Horses 

 unknown 





