I 11 111 IV V vr viT viic jx 



Fig. 12. Structural stages in evolution of upper and lower molar teeth of man. 



Scales various. 

 A-H, upper molars, left side. 



A. Upper Jurassic, triangular stage (pantotherian). 



(After G. G. Simpson.) 



B. Cretaceous, triangular stage (Deltatheridium). 



(After Gregory and Simpson.) 



c. Lov/er Eocene "tritubercular" stage (Didelphodus). 



(After Gregory.) 



D. Middle Eocene, transitional stage (Pronycticebus). 



(From Gregory, after Grandidier.) 



E. Upper Eocene, tubercular stage (Necrolemur). 



(From Gregory, after Stehlin.) 



F. Upper Miocene, primitive anthropoid (Dryoplthecus) stage. 



(From Gregory, after Pilgrim.) 



G. Pleistocene, primitive man (Le Moustier) stage. 



(After Gregory.) 



H. Recent, human stage, 

 i-ix, lower molars, right side. 



I. Jurassic, tritubercular stage, with incipient heel (Pantotherian). 



(After G. G. Simpson.) 



II. Cretaceous, primitive tuberculosectorial stage (Deltatheridium). 



(After Gregory and Simpson.) 



III. Lower Eocene, tuberculosectorial stage, with low heel (Deltatherium). 



(After Gregory.) 



IV. Middle Eocene, transitional stage (Pronycticebus). 



(From Gregory, after Grandidier.) 



V. Upper Eocene, tubercular stage (Necrolemur). 



(From Gregory, after Stehlin.) 



VI. Lower Oligocene, five-cusped proto-anthropoid stage (Propliopithecus). 



(From stereoscopic photograph by Prof. J. H. McGregor.) 



VII. Upper Miocene, five-cusped anthropoid stage (Dryopithecus). 



(After Gregory.) 



VIII. Pleistocene, primitive human stage (Le Moustier), retaining five cusps. 



(After Gregory.) 



IX. Recent, human stage, after disappearance of fifth cusp. 



(After Gregory.) 



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