200 EVOLUTION OF MAMMALIAN MOLAR TEETH 



In comparatively few mammals, however, are these four stages 

 completed. With many exceptions (such as the sectorial p^ opposed 

 by the sectorial m^ in the Carnivora), the evolution of the lower 

 premolars is normally correlated with that of the upper premolars, 

 which agree roughly with the seven upper premolar types enumerated on 

 pages 194, 195. For example, in the Equidae, three of the corresponding- 

 upper and lower premolars assume the molar form, but in Gfaleopithecus, 

 p^-'-^ become molariforrn, while the independently adaptive p-^-^- become 

 elongate and denticulate. 



