170 



INVOLUTION OF MAMMALIAN MOLAR TEETH 



superior molar (A, m 2 ), and in the lower molars (0, m l5 w 2 ) the 

 paraconid still persists. The intermediate cusps or conules in the 

 upper molars are well developed. 



me 



FIG. 150. (Left hand figure). Upper and lower molars of Euprolofionin puercensis, from the 

 Basal Eocene (Torrejon) representing the ancestral molar patterns of Plunacodus primavv.s (right 

 hand figures) from the Lower Eocene (Wasatch). 



Various species of Protogonodon, Eiiju-ofof/oiiift and Phniacodu* thus 

 exhibit beautifully the evolution into the sexitubercular, bunodont 

 superior molar crown, out of which the upper molars of all the 

 higher hoofed animals have evolved, the crown passing from the more 



A 



m-3 



in.? fit.t dp. 4 



FIG. 151. Upper and lower molars of Euprotofionin miiirn; a small Pheuacodout Coudylarth 

 from the Torrejon Formation, Stage II., Basal Eocene, showing traces of trituberculy combined 

 witli progressive upgrowth of the basal cingulum, intermediate cu.spules and hypocone in the 

 upper molars, and with the reduction of the paraconid in the lower molars, xi. 



triangular into the more quadrate form. Similarly, the lower molars 

 lose the paraconid but retain the hypoconulid. 



SPECIAL REFERENCES. 



Schlosser, M., " Beitrage zur Kenntniss der Starumesgeschiehte der Hufthiere 

 und Versuch einer Systematik der Paar- und Unpaarhnfer," Morphol. Jakrb. 12, 

 Taf. V., VI. See especially pp. 97-112. 



Matthew, W. D., " A Revision of the Puerco Fauna," Bull. Amer. Mus. Nat. 

 Hist., Vol. IX., 1897. Especially pp. 293-320 



