138 



GREGORY : 



NOTHARCTUS, AN AMERICAN EOCENE PRIMATE 



First and Second Upper Molars 

 Plates XXXV, XLI; Text Figs. 38-40 



The oldest and most primitive member of the family Pelycodus ralstoni from the Sand Coulee beds, 

 Clark's Fork Basin, has tritubercular upper molars with only a faint suggestion of the pseudohypocone 

 on the posterior ridge of the protocone of m^ and m". The external cingulum of m\ m- rises into a faintly 

 incipient mesostyle; the crowns are relatively wider transversely than in later species, that of m^ being 

 notably wide in proportion to its anteroposterior diameter. The proto- and metaconules bear trans- 

 verse crests that run from the flattened labial slope of the protocone to the lingual slopes of the para- 

 aiid metacones ; the tip of the protoconule lies in the oblique protoloph ridge that runs obliquely from 

 the protocone outwards and downward toward the parastyle; the outer half of this ridge, beyond the 

 tip of the protoconule, may be regarded as the anterior limb of the protoconule V, of which the pos- 

 terior limb is the transverse protoconule crest mentioned above. The whole crown is surrounded by a 

 cingulum which is crenulate opposite the protocone. M'- shows the following more or less worn facets 

 for articulation with the lower molars: the tip of the paracone fitted into the external valley of m2, the 

 metacone into the valley between mo and nis; past the crista anterior of the paracone of m^ sheared the 

 posteroexternal slope of the trigonid of m2; past its crista posterior sheared the anteroexternal slope 

 of the hypoconid of m2; past the crista anterior of the metacone sheared the posteroexternal slope of 

 the hypoconid of nio; past the crista posterior of the metacone sheared the anteroexternal crest of the 

 trigonid of nis. The crest running from the parastyle tip is worn by the protoconid of m^; the protocone- 

 protoconule crest (protoloph) and the anterior fork of the protoconiile are worn by the protoconid-meta- 

 conid crest (protolophid) of mo; the tip of the protoconule is worn by the anterior tip of the crista obliqua 

 of m2; the tip of the metaconule is worn by the middle of the posterior limb of the posterior V of m2. The 

 tip of the protocone of nr fitted into the talonid basin of ni2, immediately behind the tip of the protocone 

 and on its lingual slope is a worn groove or facet, which is especially well shown in No. 15681,' which is 

 caused by the tip of the entoconid; on the posterolabial slope of the protocone, immediately external 

 to the facet last described, is a worn streak or path running obhquely posterolabially, which has been 

 worn by the tip of the paraconid of nis. Thus the region of the pseudohypocone, or posterointernal 

 cusp, which is here only in an incipient stage, is bounded lingually by the gi'oove or facet for the ento- 

 conid of m2 and labially by the groove for the paraconid of ms. (Fig. 39.) 



The detailed characters of the wearing-facets of the upper molars, as well as the general form of the 

 whole dentition, indicate that in this oldest and presumably most primitive member of the family (Pely- 

 codus ralstoni) the motion of the mandible was more vertical and less transverse than in the later species; 

 also that the small wide molars with fewer cusps gave relatively greater piercing power and less grinding 

 and cutting action; this in turn suggests that the ancestral Notharctinse were probably insectivorous, a 

 conclusion that is supported by considerable collateral evidence. 



In Pelycodus trigonodus, the succeeding stage, from the lower part of the Gray Bull horizon, m\ 

 nr are of distinctly larger size and their relative width is less in proportion to their anteroposterior diam- 

 eter ; the incipient mesostyles are more distinct and the pseudohypocones are sometimes better -developed, 

 although they are at most only an obtuse swelling on the posterior slope of the protocone. Pelycodus 

 frugivorus, as defined by Matthew (1915, p. 439), from the Upper Gray Bull beds, is more advanced 

 than P. trigonodus; one specimen referred to P. frugivorus (Amer. Mus. No. 15022) shows a well-developed 

 pseudohypocone on m^ and a small one on nr ; the contour of m-, however, is less quadrate than in later 

 types. (Plate XXXV.) 



