GREGORY: NOTHARCrUS, AN AMERICAN EOCENE PRIMATE 



57 



In many respects the lower jaw of Notharctus resembles that of some of the existing American monkeys quite as much 

 as it does that of any of the living pachyderms. Notharctus agrees with most of the American monkeys in the union of 

 the rami of the jaw at the symphysis, in the small size of the condyle, in the crowded condition of the teeth, and in the 

 number of incisors, canines and true molars, which are also nearly alike in constitution. Notharctus possesses one more 

 premolar and the others have a pair of fangs. The resemblance is so close that but little change would be necessary to 

 evolve from the jaw and teeth of Notharctus that of a modern monkey. The same condition which would lead to the 

 suppression of a first premolar, in continuance would reduce the fangs of the other premolars to a single one. This change, 

 with a concomitant shortening and increase of depth of the jaw, would gi\ e the characters of the living Cebus. A f\irtlier 

 reduction of a single premolar would give rise to the condition of the jaw in the Old World apes and man. 



"In 1873 (pp. 547-548) Cope gave the following interesting discussion of tlio relationsliip of his Tomi- 

 therium rostratum, in which he clearly recognized its primate affinities: 



The first impression derived from the appearance of the lower jaw and dentition, and from the humerus, is that of an 

 ally of the coati, Nasua. The humerus, indeed, is almost a fac-simile of that of Ncmui, the only difference being a slight 

 outward direction of the axis of the head. The same bone resembles also that of many marsupials, but the flat ilium, 

 elevated position of dental foramen, and absence of much inflection of the angle of the lower jaw, etc., render affinity with 

 that group highly improbable. The length of the femur indicates that the knee was entirely free from the body, as in the 

 Quadrumana, constituting a marked distinction from anything known in the Carnieora, including Nasua. The round 

 head of the radius indicates a complete power of supination of the fore foot, and is different in form from that of Carnt- 

 vora, including Nasua; and, finally, the distal end of the radius is still more different from that of Nasiia, nnd resembles 

 closely that of Scmnopithecus. 



We have, then, an animal with a long thigh free from the body, a forefoot capal)le of complete pronation and supina- 

 tion, and a form of lower jaw and teeth ciuite similar to that of the lower monkeys. The form of the humerus and its 

 relative length to the femur, are quite as in some of the lemurs. The most marked difference is seen in the increased 

 number of teeth; but in this point it relates itself to the other Quadrumana, as the most ancient types of Carnivora and 

 Ungulates do to the more modern: c. g., Hya^nodon to the former, and Palwosyops to the latter. In its special dental 

 characters it shows a close resemblance to small types of the Eocene, which have been regarded as low Perissodactyles, as 

 Ilyopsodus, &c. 



By this time the affinities of Notharctus and its allies with the Quadrumana had been recognized 

 but the misleading suggestion of remote relationship with the "pachyderms" still persisted. In 1876 

 Cope introduced another very confusing idea which was destined to becloud the real affinities of this 

 group for a long time. Because of an erroneous and accidental association of certain creodont foot bones 

 with the limb bones of Pelycodus, Cope inferred that these animals were related to the creodonts: 



It is apparent that the supposed lemurine Mammalia of the type of Tomitherium, which have the formula of the molar 

 teeth 4-3, cannot be separated by ordinal distinction from the Creodonla. They differ from them, it is true, in their wholly 

 tubercular molar teeth, but relate to them in this as the bears and Procyonidce do to other Carnivora. I propose therefore 

 to constitute these a distinct group or suborder, intermediate in position between the Creodonta and the Prosimia', under 

 the name of the Mesodonla. 



I cannot find characters by which to distinguish this division from tlie Insectivora as an order (op. cit., p. 88). 



In the ensuing years, from 1872-1885 inclusive, Cope and Marsh described many other nominal 

 species of Eocene primates, but little was done toward clearing up their precise relationships with modern 

 forms, except that Cope recognized that his genus Anaptomorphus was a true lemuroid, referring it to the 

 suborder Prosimise. 



In 1884 Cope again stated his reasons for erecting the suborder Mesodonta, which he treated as a 

 division of the order Insectivora. ' ' The fragments of the skeletons of two species of ... . Pelycodus, were 

 found, which include numerous bones of the tarsus, and these are identical with corresponding parts in 

 the Creodonta and different from those of the Lemuridse" (p. 214). He then describes the astragalus, 

 portions of the femur and of the humerus, as being closely similar to those of the Creodonta. 



In 1885 (pp. 458-461) Cope gave a general review entitled "The Lemuroidea and Insectivora of the 

 Eocene Period of North America," in which he summarized his ideas regarding the relationships of lYoiharc- 



