376 POLAR PROBLEMS 



means fantastic, nor is it out of harmony with what we know of the 

 geographic history of the far south. As a theory it is worth present- 

 ing, moreover, because evaluation is possible in two ways, first, 

 through further paleontological discovery, and, second, through the 

 application of morphological methods such as Bensley^® followed in 

 his classic reconstruction of the checkered evolutionary history of the 

 tree kangaroos (Dendrolagus). 



Distribution and Ecology of the Southern Seals 



To return to the mammals, the southernmost waters are inhabited 

 by four species of typical or phocid seals, which are remarkable in 

 that they exhibit diverse structural peculiarities correlated with no 

 less distinctive habits (Barrett-Hamilton)/^ Each one represents 

 a well-marked genus which fills its own niche in the general ecological 

 system of the region, the four forms practically avoiding mutual 

 competition. They are as follows: 



Crab-eater, or white, seal {Lobodon carcinophagus) 



Weddell seal (Leptonychotes weddelli) 



Sea leopard {Hydriirga leptonyx) 



Ross, or singing, seal {Ommatophoca rossi). 



The first to be encountered by voyagers from the north is the 

 crab-eater seal, which lives among the ice packs during the winter and 

 summer, chiefly in pairs or small bands. It subsists on Euphausiids 

 and other pelagic crustaceans. Its pronged, antero-posteriorly 

 lengthened cheek teeth alternate in the opposing jaws, the curious 

 dentition thus functioning as a sieve or strainer, just as the baleen 

 of whales or the gill-rakers of certain fishes serve a like end. 



The Weddell seal is more southern in distribution, confining its 

 range mostly to the fast-ice throughout the year, although stragglers 

 sometimes reach South Georgia and other sub-Antarctic localities. 

 Its presence may usually be taken as an indication of the proximity 

 of land. It is the only one of the truly Antarctic seals to be found 

 ordinarily in large herds. Its food consists mainly of fishes, with 

 a certain admixture of bottom crustaceans, holothurians, etc. Its 

 incisor and canine teeth are protuberant and strongly developed to 

 serve not only as organs of prehension but also for use as a veritable 

 "circular saw" with which breathing and sounding holes are cut 

 through heavy ice. 



Wilson^^ has made an interesting comparison between the two 



46 B. A. Bensley: On the Evolution of the Australian Marsupialia, with Remarks on the Relation- 

 ships of the Marsupials in General, Trans. Linnean Soc. of London, Ser. 2, Zoology, Vol. 9, Part III, 

 1903. pp. 83-217. 



" G. E. H. Barrett-Hamilton: Seals, in ".\ntarctic Manual," Royal Geogr. Soc, London, 1901, 

 pp. 209-224. 



■'s Work cited in footnote 40, above. 



