60 



GREGORY: NOTHARCTUS, AN AMERICAN EOCENE PRIMATE 



significant resemblances in the lower jaw and teeth between Notharctus and the higher primates; but 

 Wortman independently arrived at similar conclusions. 



In the same paper, Wortman adduced strong evidence for removing Hyopsodus from the primates 

 to the Insectivora, and in so doing he freed the remaining primates from this confusing alliance. 



In 1903 and 1904 expeditions from The American Museum of Natural History to the Bridger Basin, 

 under the leadership of Mr. Walter Granger, discovered a well-preserved skull, several fragmentary skulls, 

 and partial skeletons representing three or more species of Notharctus, which are described below. 



In 1911 Schlosser, in Zittel's Grundzuge der Palaontologie, II Abt. (pp. 545-547), placed Notharctus 

 and Pelycodus with the Adapidse, and expressed the hypothesis that Adapts might l)e derived from Pely- 

 codus. 



In 1912 Stehlin (pp. 1287-1290), in the monograph referred to above, showed that the skull structure 

 of Adapis was fundamentally the same as in lemurs. In discussing the affinities of Adapts he showed 

 that the Notharctidse and the Adapidse were sharply distinguished by certain divergent trends in the 

 evolution of the dentition. His conclusions regarding the mutual relationships of these families were 

 expressed as follows (op. ext., p. 1289): 



Ob Adapiden und Notharctiden iiberhaupt durch ein engeres Band als dasjenige welches alle Primaten verbindet, 

 mit einander verbunden sind, halte ich fiir fraglich. Jedenfalls liisst sicli die Berechtigung einer systematischen Categorie, 

 welche die beiden Gruppen zusammenfasst, auf Grund unserer lieutigen Kenntnisse nicht erweisen. Es erscheint viel- 

 mehr vorderhand ebensowohl mciglich, dass dieselben schliesslich ihren Platz an ziemlich weit von einander entfernten 

 Stellen des Primatensystems finflen werden. 



In 1913 (pp. 250-251) and again in 1915 (pp. 421-425) the present writer stated that, as regards the 

 majority of its skeletal characters, Notharctus is closely allied to the lemurs, differing from modern lemurs 

 in the retention of a smaller bi-ain-case and in the avoidance of the peculiar lemurine specialization of 

 the incisors and canines, but none the less a lemur in the chief structural features of the skull, of the 

 vertebrae, and of the limbs. 



In the paper of 1915, above cited, the family Notharctidae was reduced to the rank of a subfamily 

 of the Adapidse, the resemblances in the skull and in the skeleton between Notharctus and Adapis being 

 regarded as an indication of descent from common ancestral stock, which had subsequently split into two 

 distinct subfamilies characterized by divergent tendencies in the evolution of the dentition. It was 

 also suggested that these divergences in the dentition were correlated with differences in the excursion 

 of the mandible in mastication, that of the Notharctinae being more transverse, that of the Adapinse 

 more vertical. 



In the same paper a new classification of the Lemuroidea was proposed in which the recent and 

 extinct families were grouped under three series: Lemuriformes, Lorisiformes, Tarsiiformes. The 

 Adapidse (including the Adapinse and the Notharctinse) were placed under the Lemuriformes, along with 

 the Lemuridse, Indrisidse, and Chiromyidae. The classification was followed by an abstract of the chief 

 provisional phylogenetic conclusions which had been reached up to that time by the writer in the course 

 of the present studies. 



In 1915 Dr. Matthew revised the Lower Eocene species of Pelycodus and Notharctus, described the 

 new and very primitive species Pelycodus ralstoni and Pelycodus trigonodus, and gave accurate figures 

 of the dentition of all the species of Pelycodus and of the Wind River species of Notharctus. After noting 

 Dr. Stehlin's observations on the important distinctions in the character and evolutionary trend of the 

 two groups (Adapidse and Notharctidse) he states (p. 434): "Dr. Gregory's morphologic studies of the 



