64 University of California Publications %n Geology [Vol. 13 



to disappear. No trace could be observed of these cusps in eitber of 

 the teeth of young or adult skulls of Arctocephalus australis which I 

 had at my disposal for comparison. 



In studying the dentition of the Otariidae, the fact is gradually 

 forced upon one that the earliest otarids slowly retrogressed from the 

 complex, flesh-tearing dentition of the land carnivores and reverted 

 back toward a simple, conical tooth most favorable for the capture 

 of elusive prey. Yet this retrogressive change in dentition was not 

 accompanied by any general degeneration, but on the contrary it 

 brought about a high degree of both physical and mental specializa- 

 tion. The series of Otariidae, so far as known, show that the molari- 

 form tooth must have undergone an indirect retrogression from a 

 tritubercular form. The simple haploclont type, with rudimentary 

 accessory cusps, is then the final culmination of this retrogressive 

 change. 



With the advent of time, as palaeontologic investigation goes on, 

 our series will become more complete and we may then be able to trace 

 the backward stages from the secondarily haplodont type exhibited 

 by the Otariidae to the tritubercular type of their predecessors. The 

 anterior and posterior portions of all the premolars in the mandible 

 of Alloelesmus are broken off, which indicate that accessory cusps 

 were probably present at least on some of the teeth ; otherwise it would 

 be difficult to explain why only those portions of a simple haplodont 

 crown would be broken off instead of any other portion. The same 

 is true of all the detached teeth referred to this form. 



It is a question of considerable importance whether Arctocephalus 

 and Zalophus are to be considered as highly specialized or as general- 

 ized forms of the Otariidae. If it is logical to suppose that the forms 

 possessing high sagittal and occipital crests are the most generalized, 

 and that those exhibiting a reduction of these crests are more special- 

 ized, then such forms as the two above mentioned genera may be said 

 to approach more nearly the archaic type. The males and females of 

 both of these genera are characterized by the possession of high crests, 

 but the occipital crest is much more reduced in Arctocephalus. Pre- 

 vious workers nearly all agree that Arctocephalus, undoubtedly, is 

 very closely related on one hand with Callotaria and on the other with 

 Zalophus and the latter in turn with Eumctopias. That being the 

 case, then both Eumctopias and Callotaria, which are characterized 

 by a considerable reduction of these crests, are more specialized. 



