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University of California Publications in Geology [Vol. 13 



of ancestry. The earliest known pinnipeds are as old or older than any bear 

 known, and the differences between these and the bears are almost as great as 

 between modern seals and bears. Thus the relationships of the bears cannot be 

 very close. The pinnipeds of the Miocene were already highly specialized and the 

 gap between them and Miocene land Carnivora is wide. The same criticism is 

 applicable to Megalictis. 



6. The superficial resemblance of the maxilloturbinals of ursids and pinnipeds 

 may be a case of convergence. When Monaehus is compared with boreal Phocidae 

 this extreme hypomycterous condition of the turbinated bones appears to be merely 

 a case of convergence. According to Gregoryiso this hypomycterous condition is 

 an aquatic adaptation for warming inspired air. Monaehus tropicalis has the 

 maxilloturbinals reduced to mere vestiges while Erignathus barbatus, an inhabitant 

 of boreal seas, has them developed to an exceedingly complicated degree. 



7. The astragalus of Allodesmus possesses a very shallow trochlea, with groove 

 on neck absent. An astragalar foramen is also present. This astragalus is very 

 unlike that of any known ursid, mustelid or amphicyonid astragalus. 



There are certain points in the soft anatomy of the Ursidae which 

 are also retained by the Pinnipeds, though many of the assumed 

 weighty characters cited by Max Weber 100 may not really be as im- 

 portant as they have been considered. The similarity of the following 

 structures in both pinnipeds and bears were considered by him to 

 indicate relationship. 



1. Absence of duodeno jejunal flexure of the long intestine which lies in a 

 simple mesentery. 



2. The division of the kidneys and liver into a number of separate lobules. 



3. The absence of Cowper 's glands in the male. 



4. Presence of deciduous and zonary placenta and bicornuate uterus. 



It has also been shown by Haig 191 that the histogenic features of the 

 kidney of the foetus of Hydrurga leptonyx place the seals in a small 

 group of Carnivora to which the bears also belong. 



Many of the characters cited by Weber may be due to convergence. 

 The investigations on the brains of pinnipeds and bears by Fish 192 

 show that while there appear to be many characters in common be- 

 tween the two groups, yet the bears differ from the majority of the 

 pinnipeds in seven points out of sixteen. The studies of Mitchell 193 



189 Gregory, W. K., The Orders of Mammals. Bull. Am. Mus. Nat. Hist., vol. 

 27, p. 428. 1910. 



ioo Weber, M., Die Saugetiere : Einfiihrung in die Anatomie und Systematik 

 der recenten und fossilen Mammalia, pp. 543-551. Jena, 1904. 



isi Haig, H. A., A description of the systematic anatomy of a foetal sea leopard 

 (Stenorhynchus leptomix) with remarks upon the microscopical anatomy of some 

 of the organs. Scot. Nat. Antarctic Exped., vol. 4, pp. 461-462, Publ. Brit. Mus. 

 London, 1915. 



192 Fish, P. A., The cerebral fissures of the Atlantic walrus. Proc. U. S. Nat. 

 Mus., vol. 26, pp. 675-688, pis. 28-29. 1903. 



193 Mitchell, P. C, Further observations on the intestinal tract of mammals. 

 Proc. Zool. Soc. London, pt. 1, pp. 183-251. 1916. 



