442 



MAMMALIA. 



ProtoJiippos in America, whose foot resembles that of Hip- 

 parion — the existing genus Eguus not appearing until Post- 

 Pliocene times. 



... 4 



Fig. 209. — Skeleton of Foot in various for^is of EquidjE. 



A, Oroliippm (Encene) ; b, AncTiitlmrium (Upper Eocene and Lower and Upper Mio- 

 cene) : c, Hipparion (Upper Miocene and Pliocene) ; d, Equus (Pliocene and Recent). 

 (Nicholson, after Marsh.) 



There seem to be two distinct lines of descent, one in America 

 and one in Europe. In America the stages are Eohippos, 

 Orohippos, Mesohippos, Miohippos, Protohippos, Pliohippos, 

 and Equus. In Europe, Hyracotherium, Palseotherium, Anchi- 

 therium, Hipparion, and Equus.'^ 



^ The living and extinct horses are tabulated as follows by Dr (Jadow : — 



Equidce. Lower molars quadrituberculate, or with two transverse 



ridges curved into two half-moons. Toes, -f, f , or ^. 



Hyracotherium 1 ^ * j Lower Eocene, England. 



Eohippos ) ' 



Palajotherium 



Mesohippos 



Auchitherium 



Hipparion 



Protohippos 



Pliohippos 



Hippidion 



Equus 



Since Eocene. 



Lower Eocene, Wyoming. 

 f Eocene to Miocene, Europe and U.S.A. 

 .< Lower Miocene, Dakota. 

 I Upper Miocene of Europe = Miohippos, U.S.A. 

 Toes, f. Upper Miocene of Europe, Asia, and U.S.A. 

 Pliocene, U.S.A. 

 Pliocene, U.S.A. 

 Pleistocene, S. America. 



Since Miocene in India ; since Pliocene in 

 Europe. During Pleistocene cosmopolitan, 

 excluding Australian region, 

 ('Classification of Vertebrata,' p. 47.) 



Toes, - 



Toes, 

 Toes, 

 Toes, 

 Toes, 



