Fish origins — fresh or salt water .' 279 



(4) The Oesel Ki fauna of eurypterids and fish, which in iisclfcan be used as an 

 argument for either fresh- or salt-water origins, but when viewed in the light of the 

 whole picture is most reasonably interpreted on the hypothesis of continental origins. 



In sum, the European record is in entire agreement with the thesis that the primary 

 home of the vertebrates in Silurian times lay in fresh waters, and adds confirmatory 

 evidence to the proof of fresh water vertebrate origins given by study of kidney 

 structure and function. It is not at all improbable that evidence may be forthcoming 

 that some vertebrates at least were euryhaline or even definitely marine in habitus 

 as early as the Silurian. But unless or until a very considerable body of data of this 

 sort — now lacking — be accumulated, I see no reason for serious consideration of a 

 marine history for the early vertebrates. As I have said on an earlier occasion, " A 

 consideration of selected portions of the evidence might permit of such an inter- 

 pretation; but examination of the entire body of facts . . . leads unmistakably to 

 the conclusion that the early vertebrates were dwellers in fresh water." 



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