190 



GREGORY: NOTHARCTUS, AN AMERICAN EOCENE PRIMATE 



To this statement Dr. Stehlin very rightly repUed in substance (p. 1519) that even in the oldest 

 representatives of the Notharctidie the pecuhar family characteristics of the upper and of the lower 

 molars were already present in an incipient stage which carried them out of the direct line of ancestry 

 of the Adapidse. While the justness of this criticism must be fully acknowledged it may be affirmed that 

 the writer never regarded any known member of the Notharctidse as genetically and directly ancestral 

 to the Adapidffi. What the original i:)assage intended and should have said was that the earliest mem- • 



Fig. 71. Comparison of the upper molars of the oldest known American and European species of Adapidfe. 



1. Peh/roilii>; rnlstoni. Amor. Mu.<^. Xo. 16089. Lower Eocene 8aiul Coulee beds, Clark's Fork Basin, Wyoming. X f- 



2. A(lii/)i.-< niiuiiri/a-i. After Stehlin. Middle Eocene (Upper Lutetien), Egerkingen, Switzerland. X 



bers of the Notharctina? had a pattern of the upper molars, which, according to accepted principles of 

 evolution, approached the common structural ground-plan " of the two divergent lines seen in the Noth- 

 arctinse and Adapina?." This common structural gi'ound-plan, doubtless of Pa^.eocene age, is also ap- 

 proached on the part of the European Eocene lemuroids l)y Adapts rutimeyeri (especially the specimen 

 figured in Dr. Stehlin's Taf. XXI, fig. 31), and from another direction by Andiotnoniijs pygmo'us (op. cit., 

 Taf. XXII, fig. 11). 



It has been noted above (pp. 60, 149) that the writer in 1915 attempted to connect the divergent 

 structural modifications in the dentition of the Adapidse and the Notharctidae with progressive differences 

 in the methods of mastication, so that the primitive structural plan or heritage came to be disguised by 

 adaptive or csenotelic differences. In commenting on this idea Dr. Stehlin says (1916, p. 1520): 



Gregory glaubt die Structurdivergenzen, welche zwischen deni Adapiden und dem Notharctidengebiss bestehen, 

 beruhen auf Unterschieden im Kaumechanismus und meint, wenn ich mir hievon Rechenschaft gegeben hatte, ware mein 

 Urtheil iiber die Beziehungen \on Adapis zu den Notharctiden anders ausgefallen. Diese Bemerkung meines geschatzten 

 Critikers ist mir unverstiindlich. Welches auch der Grund jener Structurdivergenzen sein mag, sie sind nun einmal 

 Thatsache, haben eine bestimmte Zeit gebraucht, um sich herauszubilden und sind bei der Reconstruction des Stamm- 

 baumes zu beriicksichtigen. Die Divergenz der Stammlinien muss unter alien Umstanden bis an den Zeitpunkt zuriick- 

 geschoben werden, w^o die Divergenz der Gebissstiucturen deutlich wird. Das ist die sehr einfache Logik meiner Aus- 

 fiihrungen und ich denke kaum, dass sich dagegen etwas Stichhaltiges einwenden lil-ist. Auf Gregorys Ansichten iiber 

 den Zusanmienhang \on Kaumechanismus und Gebissstructur werde ich unten noch zuriickkommen. 



The question as to the precise correlations between diverse methods of mastication and correspond- 

 ing modifications of the dentition has already been discussed (p. 149). With regard to the divergence 

 of the two groups in question, the fact remains that in the Viverridse, Mustelidse, Procyonidse, Canidse, 



2 



