EVOLUTION OF MAMMALIAN MOLAR TEETH 



upon or fully discussed by the great comparative anatomist Cope, who 

 dwelt, however, chiefly upon the basal Eocene stage. In 1887 the 

 present writer took up the subject in the earlier Mesozoic stages of 

 the evolution of the mammals, and in later years pursued it into the 

 later Eocene and all subsequent Tertiary stages. 



The theory was everywhere welcomed as a decided advance on 

 the old odontology and odontography, in which there was no unifying 

 principle either of homologies or of nomenclature. It has been applied 

 more or less throughout the whole class of mammalia, first in palseonto- 

 logical, then in embryological and anatomical lines ; but thus far only 

 to a rather limited extent by zoologists, or students of living mammals, 

 and, so far as the writer knows, still less by anthropologists. It has 

 been critically examined, discussed, and either partly or wholly adopted, 

 or entirely rejected as unproven, by various authors. 



The chief contributors to the development and critical examination 

 of the theory are the following : 



From the pakeontological standpoint, Cope, Osborn, Schlosser, Scott, 

 Earle, Kutinieyer, Lydekker, v. Zittel, Ameghino, Goodrich, Wortman, 

 Smith Woodward, Gidley. 



Among the zoologists who have either advocated or opposed the 

 theory are Lankester, Newton Parker, Fleischmann, H. Allen, Forsyth 

 Major, Dybowski, Winge, Sims, Beddard. 1 



Among anatomists, Schwalbe and Dwight have accepted the theory, 

 while Howes failed to find sufficient evidence for it. 



The most influential opponents of certain features of the theory 

 are those who have examined it embryologically, namely, Kiikenthal, 

 Rose, Taeker, Leche, M. F. Woodward. 1 



Four distinct principles have been developed in connection with 

 the general theory, as follows : 



I. FIRST PRINCIPLE. THE PRIMITIVE TRITUBERCULAR TYPE. 



The discovery of the oldest fauna of the age of mammals, or Tertiary 

 period, near the Puerco Canon in Northwestern New Mexico, was 

 announced by Professor Edward D. Cope in 1879. These small and 

 strange fossil mammals exhibited a general similarity in all the molar or 

 grinding teeth, even among animals which evidently had great diversity of 

 feeding habits. This similarity consisted in the possession of three main 

 tubercles on the crowns of loth upper and lower molars, disposed in tri- 

 angles* This was evidently a primitive type of molar tooth, and in 1883 



1 These names are placed in the general order in which the criticisms appeared. (See 

 pp. 200-227.) 



*[In addition to the main tubercles there were often smaller cuspules, "styles "and 

 " talons," but the upper molars of the Carnivores and Ungulates were all roughly speaking 

 " tritubercular," the lower molars all " tuberculo-sectorial " or of plainly derived types.] 



