VERTEBRATE PALAEONTOLOGY 



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Onohippidium Porahipporion 



Equus 



Stylohipparion 



Neohipparion 



Nannippus 



Hipparion 

 Calippus 



Magahippus 



Archaeohippus 



Hypohippus 



Anchitherium 



Miohippus 

 Mesohippus 



Epihippus 



Orohippus 



Hyracotherium 



II 



Fig. 43. Evolution of the horse. The scheme is more complex than 

 that suggested by Lull. (After Simpson 1951.) 



based on five specimens. In the former case we have a very 

 good idea of the form of the genus and the extent to which its 

 characters overlap those of related genera (that is, provided that 

 the 500 specimens are not just isolated cones of teeth!). A cer- 

 tain amount of information concerning the number of fossil horses 

 is available. Thus Simpson (1943) quotes the numbers of 

 specimens of fossil horses in the American Museum of Natural 

 History as follows : Lower Eocene 397 ; Middle Eocene 54 ; Upper 

 Eocene 11; Lower Oligocene 30; Middle Oligocene 125; Upper 

 Oligocene 39. The same author in his account of horses (1951) 

 has an appendix " where to see fossil horses." He mentions that 

 there are some fifty-two mounted skeletons of fossil horses in the 



11— IOE 



