226 



GREGORY: NOTHARCTUS, AN AMERICAN EOCENE PRIMATE 



internal cusp is reduced and the outer wall is compressed, in the monkeys of the New and Old Worlds, 

 as well as in the great apes and man, p^ is widened transversely and is bicuspid. 



The first and second lower premolars of Nothardus are small, slightly compressed, conical teeth, more 

 like those of other primitive Eocene mammals than those of later primates. The third lower premolar, 

 which is homologous with the anterior premolar of man and his allies is a compressed two-rooted tooth 

 with a high anterior cusp and an extremely small rudiment of a posterointernal cusp. The fourth lower 

 premolar, equivalent to the posterior premolar of later primates, has begun its transformation into the 

 molar type, that is it possesses an imperfectly differentiated anterior trigonid and a low, small talonid, 

 a primitive condition as compared with the \'ariously modified posterior premolars of higher types. In 

 the lemurs for example, it becomes much compressed, in the platyrrhines it is shortened and usually more 

 bicuspid; but some primitive forms, e. g. Nyctipithecus, retain traces of the talonid; in the catarrhines 

 it becomes bicuspid with a blunt wide talonid; in man it becomes entirely bicuspid. 



The first and second upper molars of Nothardus retain clear traces of the tritubercular pattern, which 

 is characteristic of primitive Eocene mammals ; but this pattern is modified by two features of progressive 

 specialization: first, the presence of a fourth, posterointernal cusp or pseudohypocone (which in this sub- 

 family represents a posterior budding from the main anterointernal cusp or protocone) ; secondly, the 

 presence of a mesostyle or external intermediate cusp, lying at the point of union of the two external Vs 

 or cutting wedges. This general type of upper molar has been several times evolved in various races 

 of mammals which have changed from a partly insectivorous to a more frugivorous or vegetation diet. 

 It is correlated with a slight lateral swing of the mandible in mastication. The third upper molar lacks 

 the posterointernal cusp or "pseudohypocone." The molars have distinct internal cingula, a feature 

 which is lost in many later primates. So far as the available evidence indicates the molar pattern of 

 Nothardus may well be ancestral to those of the New World primates. 



The ancestors of Nothardus, of the genus Pelycodus, which have been followed back far into the 

 beginning of the Lower Eocene, show a closely graded series of stages in the evolution of the pseudo- 

 hypocone, leading back to a nearly simple tritubercular type. The pure tritubercular pattern was very 

 probably characteristic of the as yet undiscovered Paleocene ancestors of the whole primate series. 



The general pattern of the crown of the first and second lower molars is similar to that of many 

 Eocene mammals: each molar bore fom' main cusps arranged in two transversely placed pairs, and a 

 vestigial anterior cusp or paraconid. The anterior pair, consisting of the anteroexternal cusp or pro- 

 toconid and the main anterointernal cusp or metaconid, were joined by a low transverse crest, the 

 protolophid ; the talonid or posterior moiety of the tooth bore a broad V on the posteroexternal cusp or 

 hypoconid and a low posterointernal cusp or entocoriid. The third lower molar also bore an elongate 

 third lobe or hypoconulid and its entoconid was reduced. The molars were all provided with external 

 cingula. This quadri tubercular type of lower molars is structurally ancestral, except perhaps in minor 

 details, to the lower molars both of lemuroids and of higher primates, including man.^ In the ancestral 

 Pelycodus the anterior moiety of the molar crown consists of a small highly-set triad, or trigonid, of cusps 

 followed by a low broad talonid. In association with tritubercular upper molars and small size these 

 more or less " tuberculo-sectorial " lower molars of Pelycodus give evidence that the remote ancestors of 

 Nothardus were probably more insectivorous and less frugivorous than the later genus, which may well 

 have subsisted upon fruits, eggs, small birds, and insects, as in many recent primates. 



1 Cf. Bull. Amer. Mus. Nat. Hist., XXXV, pp. 2:39-;355. 



