GREGORY: NOTHARCTUS, AN AMERICAN EOCENE PRIMATE 



185 



Summary of the Divergent Evolution of Adapinte and Notharctin^ 



NOTHARCTINyE 



Upper and lower ineisors of insectivorous-i'rugivorous type. 



Canines caniniform, but rounder in seetion. 

 Premolars becoming wider transversely. 



Anterior external cusp of p' retarded; close to posterior 

 cusp. 



P4 retarded, with small talonid. 

 Mesostyles, upper molars with Vs. 

 Pseudohypocones. 



Protolophs and protolophids less emj)liasizefl. 

 Metacristids absent. 



Paraconids present in early types, usually reduced or absent. 

 Entoconids progressive. 



Excursion of mandible progressively ental. 

 Lower jaw elongate with large high coronoid. 



Condyle of jaw very convex with internal posterior ex- 

 tension. 

 Skull mesocephalic. 



Orbits larger. 



Malar less robust, not extending to glenoid. 

 Pterygoid fossae small, slit-like. 

 Basicranial region less expanded transversely. 

 Condylar foramen remaining separate from foramen 

 lacerum posterius. 



Adapin.e 



All incisors with wide chisel-like edges (specialized frugi- 

 A orous type, probably adapted for cutting off stems). 



Canines dagger-like (adapted for piercing tough rinds?). 



pi-3 becoming more or less compressed and trenchant (A. 

 pari.sicusis). 



V* witii two external cusps, tlie posterior well separated 



from the anterior cusp. 

 P4 progressive with large talonid. 

 No mesostyles, no V's on upper molars. 

 True hypocones. 



Protolophs and protolophids conspicuously devclojx'd as 



cutting crests. 

 Metacristids typically de\ eloped. 

 Paraconids absent. 

 Entoconids retarded. 

 Excursion of mandible more orthal. 



Lower jaw short with greatly expanded angle and short 



deep ramus. 

 Condyle of jaw flatter. 



Skull wide. 



Sagittal and lanibdoidal crests very high. 

 Orbits smaller. 



Malar very stout, extending nearly to glenoid. 

 Pterygoid fossae expanded. 

 Basicranial region wider. 



Condylar foramen typically continent with foramen 

 lacerum posterius. 



4 



The evolution of the molar teeth in the Notharctinir was outlined by Professor Osborn in 1902. In 

 1915 Dr. Matthew described the two oldest and most primitive species, Pelycodus ralstoni, from the base 

 of the Lower Eocene, and its successor P. trigonodus; he hinted that the latter gave rise respectively to 

 P. frugivorus and P. jarrovii, and that these two in turn passed into the two most ancient species of 

 Nothardus, N'. nunienus, and A^. venticolus of the Wind River (Lost Cabin) formation. In 1917 Mr. 

 Granger and the present writer, revising the species of Nothardus, were enabled to connect the most 

 advanced stage, N. crassus of the Upper Bridger (formerly assigned to a separate genus Tehnatolestes) , 

 with less advanced species of the Lower Bridger, through the newly described form N. pugnax. In the 

 present work all the material has been closely restudied, with reference not only to phyletic relationships 

 but chiefly for the purpose of tracing the evolution of the dentition as a whole and of following the detailed 

 changes in the incisors, canines, premolars and molars. (Plates XXXV-XXXVII.) 



With regard to phyletic relationships the conclusions above mentioned have seemed upon re-examina- 

 tion to be justified by the available evidence. The very progressive line culminating in A^. crassus seems 

 to be clearly foreshadowed in all its characters l)y the relatively progressive A', venticolus of the Wind 

 River, while the smaller and more conservative species A^. osborni, N. viatthewi, if not representing the 

 females of some of the larger forms, bear more resemblance to the primitive N. nunienus. The chief 



