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University of California Publications in Geology [Vol. 13 



and the enlargement of the intervertebral foramina in an adaptation 

 to pelagic life. The pinnipeds possess a pelvis more nearly parallel 

 to the vertebral column than do any of the terrestrial carnivora. 



The length of the skull of the pinnipeds seems to be conditioned 

 largely by the length of the jaw, and its shape, as previously pointed 

 out, is largely the result of certain muscular adaptations. In no 

 case, excepting Mirounga, do we find the elongation of the head, 

 which is usually so characteristic of prolonged aquatic adaptation. 

 In most cases the face is short, while the cranium may be nearly 

 flat as it is in the genera, Phoca, Monachus, Erignathus and Cysto- 

 phora. It has been stated by Williston 190 that "it seems to be a 

 law of evolution that no large creatures can give rise to races of 

 smaller creatures, " and that "the largest sea animals have been the 

 final evolution of their respective races." As the history of the 

 animals in the past appeared to confirm this, it was assumed by some 

 that the sea lions, walruses, and elephant seals therefore represent a 

 higher degree of specialization than do the smaller seals and that the 

 latter approximate more nearly in size the ancestral group. Further- 

 more, Pocock 197 has found in many instances within the limits of a 

 single order that the species which were defective in the matter of 

 vibrissae were the higher derivative types, whereas those in which all 

 or most of the vibrissae persist were the most generalized types. He 

 found that in the Pinnipedia only the mystacial and superciliary tufts 

 of vibrissae were retained. In the Otariidae the supercilliaries were 

 short and few, while in the Phocidae they were well developed. 



On the other hand, the Phocidae show many evidences of being 

 the most specialized. For instance, the hind limbs have undergone a 

 greater modification than those of either the Odobenidae or Otariidae 

 and are consecuiently no longer capable of being turned forward in 

 progression on land. The external nares are more dorsal in the 

 Phocidae than in either of the others. The testes are inguinal and not 

 scrotal as they are in the Otariidae. Many other modifications could 

 be cited. 



In some respects the Odobenidae appear to have been under the 

 influence of water the longest, namely, in the possession of a heavy 

 and dense skeleton in correlation with its bottom feeding habits, in 

 the moving of the lower canines over into the molariform series and 



196 Williston, S. W., "Water reptiles of the past and present, p. 61. Chicago 

 Univ. Press. 1914. 



iot Pocock, E. I., Proe. Zool. Soc London, p. 912. 1914. 



