62 



GREGORY: NOTIIARCTI'S, AN AMERICAN EOCENE PRIMATE 



9. Wortman's suggestion that the Adapidie, including Nntharctus, stand near to the l)eginnings of 

 the monkeys and apes, especially the New World monkeys. 



10. The discovery of a well-preserved skull and of partial skeletons of Notharctus, which, as shown 

 in the present work, exhibit \evy fully the primitive lemuroid structure of the skull and skeleton. 



11. The demonstration by Stehlin of the great variety and wide differentiation of the primates 

 of the European Eocene; his exposition of the complexity and difficult nature of the problem of the rela- 

 tionship of the Eocene families with each other; his conclusions that none of the Eocene families can be 

 positively connected with modern families and that the final consideration of the problem of the place 

 of origin of the order had better be deferred until the fossil records of the Eocene of Asia become avail- 

 able. 



THE LIMBS OF XOTHAHCTrS: A ( O^LPARATIVE STl'DY 



The general conclusions from the following study of the backbone and limbs of Notharctus are stated 

 below (p. 221), but it may also be noted here that this type of skeleton has been preserved with compara- 

 ti\-ely minor changes in some of the modern lemurs, especially Lomir, Lepilemur, and Propithecus, the 

 chief difference being that these animals have longer hands and feet and longer limb bones. The foot 

 and limb bones of Adapts, so far as known, conform to the same general lemuriform type and in many 

 respects are even closer to those of existing lemurs. 



In the following description the limbs and vertebrie of A'oihardus are compared, for the sake of 

 brevity, chiefly with those of Lemur varius, Lemur inongoz, Propithecus, Cebus, and Cercopithecus, but 

 with frequent reference to other forms. These comparisons, although usually brief, establish the fact 

 that on the whole, in the characters of the vertebra^, pectoral and pelvic arches, and limbs, Notharctus 

 stands much closer to the above named lemurs than to the representatiA'es of any other group of primates; 

 also that the South American primates are structurally nearer to N^otharctus than are the Old World pri- 

 mates. 



Every limb bone of N^otharctus is fundamentally similar in all its parts and processes to the corre- 

 sponding elements in modern lemurs, the differences being solely in the degree of development of homol- 

 ogous parts. Consequently much definite knowledge of the musculature and limb movements of one 

 of the most primitive known primates can be gained by comparison with modern lemurs, the only neces- 

 sary assumption being that in rather closely related animals homologous processes and crests are usu- 

 ally connected with homologous muscles. With this purpose in view the limb muscles of a recent 

 Letnur mongoz ha^'e been carefully dissected and constant use has been made of the beautiful illustra- 

 tions of the musculature of the indrisine lemurs in Milne Edwards' memoir on the lemurs of Madagascar. 

 (Cirandidier and Edwards, 1875). 



The skeleton material of Notharctus described below comes chiefly from the Lower Bridger formation 

 (Horizon B) of Wyoming. In the principal specimen (Amer. Mus. No. 11474), the paratype of Notharc- 

 tus oshorni, all those parts of the backbone, girdles, and limbs are preserved which appear in darker 

 color in Plate XXIII. The remaining parts, shown in light gray color, were restored by Mr. Albert Thomson 

 chiefly from modern lemurs. 



A second specimen, Amer. Mus.' No. 11478 (Plate XXIV), although very imperfect, supplied some 

 important details which were missing in the first. It was associated with parts of the dentition which 

 were determined as N. tyrnnnus (Marsh). It is somewhat larger than the first skeleton, as shown 

 below, but otherwise the differences between them are trivial. 



