INTRODUCTION 



The present series of studies on the Evolution of the Primates is addressed not only to palaeontologists 

 but to anatomists and anthropologists, to students of the dentition of mammals, and to all who are con- 

 cerned with the origin, evolution, and functions of the human skeleton. The main objects of the series 

 are, first, to state and illustrate the anatomical facts without bias or prejudice, and, second, to determine 

 as far as possible the main evolutionary stages through which the observed anatomical conditions have 

 been attained and towards which they may point. 



Naturally, such evolutionary conclusions and evaluations as are adopted in this work result from 

 a comparison of the observed conditions with a general background or concept of evidence, which in many 

 cases could not be fully exposed without lengthy discursions from the immediate topic. For example, 

 the conception of the successive stages of the evolution of the limbs of primates outlined at the end of 

 this work rests upon the following classes of evidence. 



(1) Evidence concerning the origin of mammals from Permo-Triassic therapsid reptiles. It would 

 be presumptuous for the writer to take anything for granted with regard to this topic or even to touch it 

 at all, if he had not always endeavored to make good the opportunity (afforded by the resources of this 

 Museum and by his friendship with Professor Williston, Dr. Broom, Dr. D. M. S. Watson and others) 

 of acquiring "autoptic knowledge" of the Palaeozoic Tetrapoda, and especially of the Permian and Tri- 

 assic mammal-like reptiles, a considerable collection of the latter being under his care and frequently 

 studied by himself and colleagues. 



The problem of the origin of the mammals has, of course, an immediate bearing upon the origin 

 of the primates, including man, and thus has at least a potential value and interest to anatomists, anthro- 

 pologists, and others, as well as to palaeontologists. But if there be anatomists who still uphold the view 

 that mammals have been derived from amphibians rather than from late Palaeozoic reptiles, or if there be 

 others who regard such problems as still in the purely speculative stage, the writer can only refer, in this 

 work, to the growing literature ^ of the subject, or suggest a re-examination of all the evidence in the 

 light of modern comparative anatomy. 



(2) A second class of evidence, which is largely taken for granted in the discussion of the ex'olution 

 of the limbs of primates, relates to the following ciuestions. What primitive characters of the limbs 

 and axial skeleton should be ascribed to the very little -known Cretaceous ancestors of the various orders 

 of placental mammals? Was there ever a single group of primitive placental mammals? Or are the 

 placental orders polyphyletic derivatives of different orders of pre-placentals? And did a central stock 

 give rise by adaptive radiation to the already differentiated placental orders and families of the Paleo- 

 cene? Answers to such questions have long been sought by investigators in this Museum through a 

 study of the representatives of many orders and families of Paleocene and T^ower Eocene placental mam- 

 mals, and of the clearly demonstrable divergent trends of evolution exhibited in many of these phyla 



1 Cited and reviewed especially in the following papers : 



Watson, D. M. S. 1911. The Skull of Diademodon, with Notes on those of some other Cynodonts. Ann. Mag. Nat. 

 Hist., (8) VIII, pp. 29.3-330. [Resemblances of Therapsids to Mammals, pp. 32.5-326.] 



Gregory, W. K. 1913. Critique of Recent Work on the Morphology of the Vertebrate Skull, Especially in Relation to 

 the Origin of Mammals. Journ. Morph., XXIV, No. 1, March. 



Broom, R. 1914. Croonian Lecture On the Origin of Mammals. Philos. Trans. Roy. Soc. London, (B) CCVI, pp. 1-48. 



Gregory, W. K., and Camp, C. L. 1918. A Reconstruction of the Skeleton of Cynognathus. Bull. Amer. Mus. Nat. Hist., 

 XXXVIII, pp. 447-563. 



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