GREGORY: NOTHARCTUS, AN AMERICAN EOCENE PRIMATE 



187 



Lepileymir. It thus seems likely that Adapts parisiensis lived upon some small fruit with a tough rind. 

 The sharp chisel-like incisors would be adapted for cutting the fruit from the branches, the canines would 

 pierce the rind and the premolars would cut it into large pieces; the conical cusps of the fourth pre- 

 molars and the molars would break up the rind and the protoloph shear would cut it, the pestle and 

 mortar action of the protocone, and other cusps, would press the pulp without grinding it. Adapts 

 rnagnus with coarser teeth and relatively smaller muscular power may have fed upon larger fruit with 

 a proportionately less resistant rind. 



The account given in the preceding pages (1.37-139, 149) of the interlocking relations of the upper and 

 lower teeth and of the motions of the mandible is based upon intensive and repeated study of a number 

 of specimens in which it was possible to fit the lower and upper teeth together and to ascertain the exact 

 topographic relations of the parts of the upper and lower teeth during successive stages of occlusion as 

 well as the paths described by the mandible in its excursions. These studies seem to the writer to afford 

 very definite evidence in favor of the following conclusions which were set forth in a preliminary way 

 in 1915.1 



(1) In the Notharctinffi the progressive development of mesostyles, pseudohypocones and ento- 

 conids are all more or less directly correlated with " the progressive development of an ental motion of 

 the mandible in the act of "chewing on one side." 



(2) In the Adapinte the lack of mesostyles, the retarded or even retrogressive state of the entoconids, 

 the normal relations of the true cingulum-hypocone to the trigonid and the progressive development of 

 the metacristid and the emphasis of the protoloph and protolophid are all correlated with a more orthal 

 motion of the mandible. 



(3) In the early Notharctina the region of the future pseudohypocone suffers transverse attrition 

 on the lingual side by the entoconid of the corresponding lower molar, and on the posterolabial side by 

 the paraconid of the succeeding lower molar. In the final stage, N. crassus, the large entoconid tip opposes 

 the cleft between the protocone and the pseudohypocone. 



(4) In Adapts parisiensis and A. magnus the lower entoconid lies well to the inner side of the true 

 hypocone and seems to have no very direct relations with it. 



(5) The very retarded development of the second external cusp (metacone) of p* in the Notharctinse 

 is connected with the anteroposterior crowding of the premolars and the very retarded development of 

 the hypoconid of pj, while in the Adapinae the early appearance of the metacone of p^ is correlated with 

 the precocious lengthening of the premolar series and the appearance of a well-developed hypoconid on pj. 



From the little that is known of the postcranial skeleton of the Adapinse, it is evident that the limbs 

 were fundamentally similar to those of Nothardus the chief difference being that the calcaneum, if 

 correctly referred to Adapis, was shorter. 



1 Bull. Geol. Soc. Amer., XXVI, pp. 422, 423. 



-The words "correlated with," as used above do not mean "caused by." The divergent trends in the evolution of the patterns 

 of the teeth in Notharctinte and Adapinae are associated with progressive differences in the functions and mechanical relations of the 

 parts and with equal differences in the movements of the lower jaw; but for present purposes it is not ncci"ssai \' ((j drcnlc whether the 

 changes in function followed upon orthogenetic changes in dental pattern, whether diverging environmcnlal conditKins resulted in 

 the selection of divergent functions and structural patterns, or whether lioth procL-sses contributed to the (ibjective results which alone 

 are matters of observation. 



