ORDINAL TYPES OF MOLARS: PINNIPKDIA 143 



(p. 10.')); 00 the enlargement of the paraeone and reduction of the 

 metacone occurs also in Dinocyon (Fig. 99), in the Mesonychid Creodonts 

 (Figs. 87, 88, and p. L'lO), and is probably secondary: () no fossil 

 ancestral viverrines are known with such aberrant molars. 



M'KCIA L REFERENCES. 

 Figures of Molars of ( 'arnivora. 



Bronu, H. G., Klass. u. Orel. <!. TiderreicKs, Bil. I., pp. 17!)-i'Oi'. 

 Owen, R., Odontograpky, 1840-1845. See especially for histology of the teeth. 

 Giebel, C. G., Odontograpfiie, 1855. 



Schlosser, M., Die Aff<'/i . . . Carnivoren de* Enrnpiiischeii Ti-rfft'irx, etc. Wien, 

 1887-90. 



PlNNIPEDIA. 



The teetli of the aquatic Carnivora, or Pinnipedia, are so much 

 modih'ed secondarily that until we trace their ancestral history we 

 cannot feel any confidence in attempts either to homologize the cusps 

 or to trace these teeth back to a tritubercular or triconodont stage. 

 Weber l adduces much evidence in favour of their derivation from the 

 Bears. In that case the ultimate derivation of their molars from the 

 tritubercular type would be obvious. 



As figured above, Phoca gichigensis (Fig. lOo A) exhibits a tooth 

 analogous to that of the Triconodonta among the primitive Marsupials 

 (Fig. 6), that is, with a main central and two lateral cusps. We 

 have seen that somewhat similar molars with several cusps in a fore- 

 and-aft line have evolved secondarily out of tuberculo-sectorial molars 

 in the case of the Marsupial Thylacymis (Fig. 58, II. g) and of the 

 Creodonts Mesonyx (Fig. 87, lower teeth) and Hycenodon (Fig. 91). 



Phoca, vitulina exhibits a type more suggestive of Zcuglodoii 

 (Fig. 194, p. 191), the central cusp is less prominent, and the lateral 

 and posterior cusps more elevated and connate. According to Dr. 

 J. A. Allen,' 2 within this single species, Phoca vitulina, there is a wide 

 range of individual and sexual variation in the cheek teeth, as 

 regards the number and position of the cusps, the size of the crown, 

 its position in the tooth row, etc., so that we may infer that at 

 least in this species a high rate of evolution or variation is even 

 now in progress, while in the past the evolution has obliterated the 

 primitive pattern of the teeth. In Phoca f/rcenlandica the lower molars 

 are suggestive of the tuberculo-sectorial type. 



The third type, Zalophus calif or nianus, the Sea-lion (Fig. 103 0), 

 presents in the upper molars at least an example of the secondarily 

 haplodont croini, in which the main outer cusp is probably the paracone, 



1 Die Sauyetiere, 8vo, 1904, p. 551. 



'-Bull. Amer. Mus. Nat. ///*/., Vol. XVI., 1900, pp. 468-470. 



