54 



GREGORY: NOrilARCrUS, AN AMERICAN EOCENE PRIMATE 



during Paleocene and subsequent times. Cope and Wortman, the great pioneer collectors and students 

 of Paleocene mammals, pointed the way for the systematic series of explorations of the early Tertiary 

 horizons of the West which has been sent out year after year by this Museum under the direction of Pro- 

 fessor Osborn and in charge of Mr. Walter Granger. The many thousands of specimens collected from 

 these early horizons have been accurately recorded as to geological level, and have been or are being 

 described in the faunistic and systematic studies of Osborn, Matthew, Granger, and others as noted below 

 in the bibliography. This is the material upon which are based many statements in this paper as to 

 what are here regarded as primitive placental characters. 



A related class of evidence referred to in other parts of this work deals with the origin and evolution 

 of the dentition of placental mammals. This has been so often discussed in previous works by Professor 

 Osborn ^ and the writer " that it may be dismissed here with a brief statement of the writer's concept of 

 the dentition of the primitive placental mammals perhaps in a Mid-Cretaceous stage of development: 

 dental formula of adults of deciduous dentition jj;}^; dentition on the whole more or less like that 

 of an opossum. Opposite upper incisors arranged in convergent series, overhanging lower incisors, 

 canines caniniform, the tip of the lower canine received in a pit in the maxilla, in front of the upper canine; 

 first three premolars simple, but gradually becoming more like pf ; p^ bicuspid with a metastyle shear, p4 

 submolariform with low talonid; upper molars acutely triangular in form, extended transversely, lower 

 molar trigonids fitting into spaces between upper molars, hence protoconid-paraconid shears of lower 

 molars shearing past metacone-metasty le shear of uppers ; talonids of lower molars overlapping on crowns 

 of uppers, narrow transversely, their hypoconids fitting between the barely separated para- and meta- 

 cones. 



Such forms and relations of the upper and lower teeth are more or less completely retained in the most 

 primitive known members of many phyla of Eocene carnivores, insectivores, and primates. They were 

 originally associated with orthal jaw movement, stout zygomatic arches, a long face with rather small 

 orbits, and very narrow brain-case surmounted by a sagittal crest. The primates very early lost one 

 pair of incisors in each jaw, shortened the face, and enlarged the orbits and brain-case; but Nothardus 

 and its predecessors had not yet gone far along this line of advance since they retained a comparatively 

 small brain-case and very many primitive characters of the dentition. 



A vast field of evidence afforded by comparative anatomy, taxonomy, and paleontology quite clearly 

 indicates, in the writer's opinion, that the general stages in the evolution of the vertebrates from the 

 most primitive gnathostomes of the Ordovicic to man, with their approximate geological horizons, were 

 as follows: 



Stage 1. ? Ordovicic. Primitive gnathostomes with gill-arch jaws and cartilaginous endoskeleton. 

 Stage 2. ? Siluric. Primitive rhipidistian fishes. 

 Stage 3. Devonic. Protetrapoda.^ 

 Stage 4. Carbonic. Proreptilia. 



1 Osborn, H. F. 1907. Evolution of Mammalian Molar Teeth, To and From the Triangular Type. Edited by W. K. Gregory, 

 New York: The Macmillan Co. 



2 Gregory, W. K. 1916. The Cope-0.sborn "Theory of Trituberculy " and the Ancestral Molar Patterns of the Primates. Bull. 

 Amer. Mus. Nat. Hist., XXV, pp. 2.39-257. 



Gregory, W.K. 1918. The Evolution of Orthodonty. The Dental Cosmos, May, 1918. 



' This word is here used as defined by Cope (1887, Amer. Naturalist, p. 991), noting the movement of the jaws in a vertical plane 

 as in the carnivorous mammals. Some authors use orthal as if it meant movement in an anteroposterior direction. 



* See Gregory, W. K. 1915. Present Status of the Problem of the Origin of the Tetrapoda, with Special Reference to the Skull 

 and Paired Limbs. Ann. N. Y. Acad. Sci., XXVI, pp. 317-383. 



