156 



INVOLUTION OF MAMMALIAN MOLAR TEETH 



the lower molars are also obviously derived by depression of the 

 trituberctilo-sectorial pattern. 



Opinions differ as to the value of the evidence that these forms 

 are true ancestors of the American Edentates, but the balance of 

 structural characters is certainly very strongly in favor of this theory. 

 If it shall be finally positively confirmed by future discovery, the 

 American Edentata will also be definitely ranged in the tritubercular 

 ranks. It should be stated, however, that Professor Scott seriously 



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ni.2 



en" 



me'' 



m-3 



Fie. 125. Crown view of unworn lower molars of Culnmodon simplex, family Stylinodontidse, 

 order Taniiodonta, from the Wasatch Formation, Lower Eocene, x -| . Molars apparently derived 

 from the tuberculo-sectorial type by the loss of the paraconid (compare analogous conditions 

 among Primates and Ungulates). (From Wortman, after Scott and Osborn.) 



FIG. 12G. Single tooth and fragment of the lower jaw with teeth of Sti/linodon minis, family 

 Stylinodontidfe, order Tfeniodonta, from the Wind River Formation, Stage II., Lower Eocene, 

 representing a highly specialized Taeniodont with hypsodont rootless cheek teeth, which have 

 lost the enamel on the inner and outer sides, and all traces of tuberculo-sectorial derivation, x 4. 

 (From Wortman, after Marsh.) 



questions the supposed ancestral relationship of the Tteniodonta to the 

 American Edentates, because he says the Tseniodonts are much less 

 like the Santa Cruz Miocene Ground Sloths than like the descendants 

 of the latter, the Pleistocene Ground Sloths ; and hence he interprets 

 the resemblances between Ganodonts and Edentates as an instance 

 of convergent evolution. 



SPECIAL REFERENCES. 

 Owen, B., Odontography, 1840-45. 

 Giebel, C. G., Odontographie, 1855. 

 Bronn, H. G., Klassen u. Ordnungen des Tlrierreich's, Bd. I., pp. 147-150. 



