ORDINAL TYPES OF MOLARS: TI LLODOXTIA 



151 



points out that the hypsodont and folded molars of Stencojibcr, Palccocaxtm- 

 and Castor, may have been derived from the more brachyodont teeth 

 of Sciuranis, which in many respects is closely related to Paramys. 

 ' In like manner Mysops and Sciu-mn/v afibrd the stem types from 

 \vliich both the Hystricomorphs and Myomorphs were in all probability 

 derived/' All of this, if proved, would show (1) the derivation of all 

 Rodent molars from the brachyodont Sciuromorph type, and (2) that 

 the nomenclature of Trituberculy could only lie applied to the molar 

 cusps of Rodentia as a matter of convenience not as indicating homologies 

 with similarly placed cusps in other orders. 



SPECL I /> REFERENCES. 

 Owen, R., Odontography, 1840-45. 

 Giebel, C'. G., Odontographie, 1855. 



Broim, H. G., Klas*. K. Ord. des Thierreidts, Bd. I., pp. 150-169. 

 Tullberg, T., System der Nngethiere. Upsala, 1899. 



Schlosser, M., " Die Differeuzienmg des Saugetiergebisses," Biol. CentralbL, 

 Bd. X., Nr. 8 u. 9, 1890 (especially pp. 250-251). 



TlLLODONTIA. 



Esthonyx from the Wasatch or Lower Eocene almost certainly 

 represents an early stage of the Tillodontia. 1 The pure trituberculy 

 of its molars brings this group also in line with the great majority 

 of early mammals. (Fig. 116.) 



mTs 



FIG. 11(3. Upper cheek teeth of Esthmu/.:- <i,'-i<tii(enfs, a Tillodont from the Wind River 

 Formation, Lower Eocene, representing the ancestral pattern from which the Tillotl,, ,-ii<-,,i 

 teeth must have been derived, x A. 



EDENTATA AND TJGXIODONTA. 



The teeth of all the known specialized Edentates are so highly 

 modified not only ly the loss of enamel, but by the simplification of 

 the pattern of the crown to a conical or haplodont condition, to a 

 tubular condition, or to the compressed columns of the (Jravigrade 

 Sloths, that until recently no light whatever was thrown by comparative 

 zoology on the ancestral forms of the molar teeth. The first discovery 



J See Wortman, J. L., in Bull. Ame.r. Mm. A T /. Hint., Vol. IX., 1897. 



