144 



EVOLUTION OF MAMMALIAN MOLAR TEETH 



which has been developed at the expense of the degenerating . inner 

 cusps, which included originally an elevated protocone. 



The secondarily triconodont cheek teeth of the Leopard Seal 

 (Ogmorhinus leptonyx] are shown in Fig. 42*. 



SPEC I A L REFERENCES. 



Bronn, H. G., Klassen und Ordnungen des Thierreic/i's, B<1. I., pp. 105-108. 



Owen, R., Odontography. 



Tomes, C. S., A Manual of Dental Anatomy, 1898. 



De Blainville, H. D., Osteogruphie des Mammi. feres. 



>>>'> 



Fio. 103. Secondary evolution of triconodont and baplodont types in Pinnipedia. Internal 

 view. A. Phoc'a gichigensis (family Phocidae or Earless Seals). B. flioca ritulhia (Harbor Seal). 

 C. Zalophus California us (California Sea Lion, family Otariidse or Eared Seals). Allx i. 



PtODENTIA. 



We naturally look among the brachyodont, short-crowned types 

 of Rodents, such as the squirrels and mice, for the ancestral form 

 of Eodent teeth. Matthew 1 and Osborn 2 have hypothetically traced 

 the Kodents back to a lower Eocene ancestor in the family Mixodec- 

 tidae ; Osborn has gone so far as to call these animals Proglires, 8 

 whereas Wortman 4 has revived the view expressed by Cope that 



1( 'A Revision of the Puerco Fauna," Bull. Amer. Mas. Nat. Hist., Vol. IX., 1897, 

 pp. 259-323. 



2 " American Eocene Primates and the Supposed LJodent Family Mixodectidfe," Bull. 

 Amer. Mus. \at. Hist., Vol. XVI., 1902, pp. 203-213. 



3 Recent studies by Matthew indicate the nearer affinity of these animals to the 

 Insectivora, with possible relations to the Lemuroids. 



4 " Studies of Eocene Mammalia in the Marsh Collection, Peabody Museum," Amer. 

 Journ. Sci., Vol. XVI., Nov. 1903, pp. 345-352. 



