148 THE AGE OF MAMMALS 



suilline, or pig-like, forms (Suidse) embracing the larger form Choeromorus, 

 and Acotherulum, of diminutive size. 



The most striking fact regarding this as- 



Chief Mammals semblage of mannnals is that so few of them 



Lophiodonts ' ^^^ ancestral to the Oligocene mammals of 



Palteotheres *^^ same geographic, region. This is seen in 



Hvracotheres ^^^ special study of several of the groups. 



(]5rimitive horses) Three phyla of Eocene suillines. — We are 



Dicholiunids indebted to Stehlin for a masterly review ^ of 



Anthracotheres the descent of the Eocene suillines of Europe. 



Ancodonts or hyopotamids The key to the interpretation of these mam- 

 Xiphodonts mals, which have been in confusion since the 



Dichodonts time of Cuvier, is found in the discrimina- 



Anoplotheres ^io^^ of three grand phyla and several sub- 



Suillines phyla, readily distinguished by four characters, 



Lemuroids namely, through their respective dolicho- 



Sciuroids cephaly or brachycephaly, the shape of the 



Moles and hedgehogs posterior part of the mandible, the arrange- 



Hygenodonts ment of the anterior, or cutting teeth, and 



the presence or absence of a mesostyle on the 

 superior grinders. Thus Chceropotamus (dolichocephalic), Choeromorus (mesa- 

 ticephalic), Cebochoerus (brachycephalic) represent three distinct lines, widely 

 spread geographically and of great geologic range, from the Upper Lutetian 

 to Lower Sannoisian. No suoids are known from the Lower Lutetian, and 

 Choeropotamus alone survives into the Lower Sannois an. Only Leptaco- 

 theruluvi of Quercy and Choeromorus of Mormont remain as a possible 

 source of Oligocene evolution. Through the aberrant evolution of their cut- 

 ting teeth neither Chceropotamus nor Cehochoeriis can include ancestors of 

 the post-Eocene suillines. Stehlin suggests that they may be ancestral 

 to the hippopotami, which first appear in the Lower Pliocene of Europe. 



Five phyla of Eocene anthracotheres. — These animals, large and small, are 

 readily distinguished from the pigs by their selenodonty, i.e. all the outer 

 and often the inner crests of the superior grinding teeth are crescentic. In 

 this connection it is hiteresting to note that the pigs also originally pos- 

 sessed crescentic cusps, that their rounded cusps are secondary, or neo- 

 bunodont.^ Among the smaller anthracotheres {Haplohunodon, Rhaga- 

 therium) of Egerkingen, Mormont, Hordwell, Bembridge, and Quercy (of 

 Lutetian to Ludian age), as well as Lophiobunodon of Lissieu and La Levi- 

 niere, we discover five phyla which suddenly make their appearance in Upper 



^ Stehlin, H. G., Die Siiugetiere des schweizerischen Eoeaens. Critischer Catalog der 

 Materialien. Fiinfter Toil: Chceropotamus, Ceboohoprus, Choeromorus, Haplohunodon, 

 Rhagatherium, Mixtotherium. Ahhandl. schweiz. palaont. Ges., Vol. XXXV, 190S, pp. 691- 

 837. 



- Stehlin, H. G., Uber die Geschichte des Suiden-Gebisses. Abh. schweiz. pal&ont. Ges., 

 Vols. XXVI-XXVII, 1899, 1900, Pt. 1, p. 125. 



