416 BuUdiu American Museum of Natural History. [\o\. XXVII, 



Resemblances to tJte Pinnipedia. Convergent evolution is also respon- 

 sible for the points of resemblance wherein those most advanced Pinnipeds, 

 the Sea-Elephants (Macrorhinus), approach the Cetacea. Aquatic adap- 

 tation has proceeded so far in the Sea-Elephants that it is expressed not only 

 in the general form of the body, flippers, etc., but even in certain Cetoid 

 features of the base of the cranium,^ of the enlarged periotic bones and of 

 the auditory ossicles (cf. Doran, 1879). But even in regard to these struc- 

 tures Macrorhinus is clearly only a development of the normal Phocid 

 type and is separated from the Cetacean type by a host of significant 

 differences. 



Resemblances to the Edentates. The claims of the Edentates to i-elation- 

 ship with the Cetacea rest upon characters which are less obviously adaptive 

 and are therefore entitled to more serious consideration. They were first 

 advocated by de Blainville (p. 76) and recently by Beddard (1902, p. 120). 

 The latter author cites the following characters: 



" (1) the existence of traces of a hard exoskeleton of which vestiges remain in the 

 Porpoise ; (2) the double articulation of the rib of the Baltenopterids to the sternum, 

 with which compare the conditions obtaining in the Great Anteater; (3) the con- 

 crescence of some of the cervical vertebrae; (4) the share which the pterygoids may 

 take in the formation of the hard palate; (5) the fact that in the Porpoise, at any 

 rate, as in many Edentates, the vena cava, instead of increasing in size as it ap- 

 proaches the liver, diminishes." 



The Cetacea further resemble the Armadillos in the multiplication and 

 cylindrical character of the cheek teeth. 



These interesting resemblances are rather strengthened by other occa- 

 sional features, such as the carrying back of the palate in Myrmecophaga, or 

 the fi'equent presence of retia mirabilia in both groups, which seem to point 

 toward potential similarities between the remote ancestors of the two orders ; 

 but these resemblances are not numerous enough to be at all convincing and 

 are not supported by what is known of the palpeontological record, so that 

 the case for the Edentate affinities of the Cetacea can scarcely be regarded 

 as anything more than a possible hypothesis. 



RclaiioJis of the typical Cetacea to the Zeuglodontia. The problem of the 

 origin of the typical Cetaceans rests largely upon the ciuestion whether the 

 Zeuglodonts are genetically true Cetaceans or whether the resemblances 

 between Zeuglodon and Squalodon may be regarded as converge;nt. Dr. 

 True (1908) has reexamined the question of the relationships of the Cetacea 

 with the Zeuglodonts and reaches a negative conclusion. He states that 

 the humerus of Microzeuglodon (a genus which was formerly thought to 



' The skull of Macrorhinus ( = Mirounga) is figured in Elliot's ' Mammals of Middle America 

 and the West Indies ' 



