164 BULLETIN 16 9, UNITED STATES NATIONAL MUSEUM 



Measurements of the only known specimen are as follows: Length P4, 

 1.5; width P4, 1.2; length Mi, 1.2; width Mj, 1.2; length Mo, 1.2; 

 width M2, 1.3; length M3, 1.7; width M3, 1.0; Mi_3, 4.4; ratio length 

 P4 : length Mi, 1.25; ratio length Mg : width M2, 0.95; ratio length 

 M3 : length M2, 1.42. 



Family PLESIADAPIDAE Trouessart, 1897 



Although quite distinctive and manifestly in the plesiadapid line, 

 Pronothodectes shows a definite resemblance to the other primate 

 genera in this fauna. Elphidotarsius represents the beginning of a 

 divergent line, especially in the first stages of specialization of P4, but 

 there is a remarkably detailed resemblance in the molar structure. 

 The paraconids are more distinct in Elphidotarsius and the trigonid of 

 Ml more expanded anteroposteriorly. The talonid cusps of Mi_2 are 

 less distinct. Except for the here very slight difference in the para- 

 conid, the higlily characteristic M3 is almost identical in the two gen- 

 era. The resemblance to Paromomys, especially P. depressidens, in 

 the lower teeth is also very marked, the noteworthy differences aside 

 from the divergent emphasis in the anterior teeth being in the some- 

 what more progressive, or slightly different, specialization of the molar 

 trigonids and the aberrant heel structure of M3 of P. depressidens. 

 The trigonid structure, but not that of the heel of M3 is somewhat 

 more closely approached in Palaechthon. 



The very incomplete knowledge of Pronothodectes upper teeth sug- 

 gests a basic resemblance to those of other genera here described, but 

 makes it easier to see a few outstanding differences: the better para- 

 cone-metacone separation and strong conule of P* and the less- 

 marked posterointernal molar expansion in Pronothodectes, all of which 

 are resemblances to Plesiadapis. 



There can be no question that Gidley was right in considering Prono- 

 thodectes as closely related to Plesiadapis ("Nothodectes"). The prin- 

 cipal differences are clear from the description. Pronothodectes has 

 the enlarged incisor less procumbent, tooth reduction considerably 

 less advanced and diastema not developed, cheek teeth less depressed 

 and of somewhat simpler detail. In all these respects and also in the 

 smaller size of its species, Pronothodectes is more primitive than Plesia- 

 dapis, to which it seems surely to be ancestral in a structural, and 

 perhaps also in a literal sense. 



Pronothodectes represents the earliest known member of a primate 

 phylum analogous to the Elphidotarsius-Carpodaptes-Carpolestes 

 phylum but with a greater known range in space and time. Its 

 principal terms are Pronothodectes, middle Paleocene of North America, 

 Plesiadapis, upper Paleocene of North America and Europe and, prob- 

 ably, lower Eocene of North America, and Platychoerops, lower Eocene 



