216 



EVOLUTION OF MAMMALIAN MOLAR TEETH 



sought in one of the outer cusps, as it is in the premolars, which, indeed, 

 begin their complication on the inner side. In so far as this observa- 

 tion applies to the Creodonta, Condylarthra, Ungulata, there is indeed 

 much force in it. 



Scott has also expressed the belief that premolar and molar cusps are 

 in the main serially homologous ; in other words, that the molars origin- 

 ally evolved as the premolars did subsequently. 



More recently Wortman l supports the premolar analogy theory on 

 pakeontological grounds, and advises the total abandonment of the theory 

 of trituberculy, asserting emphatically that the cusps in the molars were 

 added in exactly the same manner and in precisely the same order as 

 in the premolars (Fig. 205). 



FIG. 205. Upper figure, Upper cheek teeth of Dissacus saurognathus from the Torrejon Forma- 

 tion, Stage II, Basal Eocene. Loicer figure, Upper cheek teeth of Mesonyx obtusidens from 

 the Bridger Formation, Middle Eocene. Dr. Wortman regards the Dissacus teeth as representing 

 the ancestral pattern of the Me&onyx teeth and believes the internal cusp or "protocone" of the 

 molars to be a secondary upgrowth of the basal cingtilum like the corresponding cusps of the 

 premolars.' 2 After Wortman. 



The two great facts which apparently support this theory are : first, 

 that we can actually follow the premolars passing by cusp addition from 

 the haplodont into the sexitubercular condition exactly like the molars ; 

 second, that according to the Cope-Osborn theory the protocones or 

 reptilian cones are on the outer side of the upper premolars and on 

 the inner side of the upper molars, certainly an anatomical paradox 

 which has never yet been explained away ; third, when it is further 

 considered that embryogeny or ontogeny supports this inference, that 

 in the embryos of the majority of mammals the antero-external cusp 

 (Osborn's paracone) of the true upper molars is the first to develop, 

 do we not secure a concurrence of testimony which seems irresistible ? 



'["Origin of the Tritubercnlar Molar,"] Amur. Jour. Sri., Vol. XIII.. Jan. 1902, 

 pp. 94-95; Vol. XVI., Nov 1903, pp. 365-368. 



2 [Dr. Matthew's recent investigations on the Meponychiclffi do not substantiate the 

 supposed facts on which this argument is based. EL>.] 



