212 the habitat of the eurypterida 



migration and distribution of the eurypterids 



Theory of Early Marine Habitat and Routes of Migration. 

 As I stated above, the anomalies in the distribution of the eurypterids 

 have not usually been given much consideration, though they are of 

 the utmost importance. There is a current opinion that has some- 

 how been formed about the bionomy of the eurypterid faunas and no 

 one thinks of challenging it. When a eurypterid fauna has been found 

 in a place where a marine fauna was not expected, it has had to be 

 made to fit in with the preconceived opinion about the bionomic facies 

 in which eurypterids are supposed to occur. It has been spoken of as 

 a "most unusual occurrence;" "one which is most interesting because 

 found in beds formerly supposed to be devoid of marine fossils," and 

 so on. Again we read of the clear evidence of a marine passage be- 

 tween the Buffalo region and the Baltic area, because* two almost 

 identical species of eurypterids are found in these localities. Forma- 

 tions are declared to be marine because they contain eurypterids, and 

 eurypterids are held to be marine, because they occur in formations 

 considered on a priori grounds to be marine. Every writer seems to 

 feel it necessary to fit the eurypterids into a marine or estuarine habi- 

 tat; where the facts refuse to fall into line, they are cited as ineresting 

 because they fail to, or else they are consciously suppressed or care- 

 lessly overlooked. The prevailing opinion as to the bionomy of the 

 successive eurypterid faunas is as follows: Until well on in the Siluric 

 the eurypterids were purely marine forms living in the seas and, in- 

 f erentially , associated with the marine organisms th erein . Toward the 

 middle of the Siluric, the eurypterids all over the world left the seas 

 and migrated into the various brackish water bodies then existing, 

 seeking the mouths of rivers, the bays, lagoons and interior cut-off 

 arms of the sea. From that time until the end of the Palaeozoic, 

 they are supposed to have sought water of ever-decreasing salinity 

 until they became entirely freshwater denizens. Their geographical 

 distribution is accounted for by an assumed migration from one es- 

 tuary or lagoon to another along the shores of various Palaeozoic 

 continents. 



Objections to Marine Habitat Theory. If this succession of 

 events is the correct one, then the following question arises in con- 

 nection with the distribution: If the eurypterids lived in pools or in 

 marginal lagoons on the seashore, in estuaries, bays or cut-offs how 

 did they get there to begin with? 



