PALEOBIOGEOGRAPHY OF THE MARINE REALM 



173 



efifect, the thermal influence on oceanic circulation, and the general 

 relief and land connections, we have named the paleoclimatic and 

 paleocurrent factors that can profitably be considered, and which 

 give rise to the broad biogeographical subdivisions of land and 

 sea, best reflected on a worldwide basis by the distribution of 

 marine plankton (Fig. 7). 



Employing a rotating tank apparatus similar to that of von Arx 

 (1957) to create patterns of oceanic circulation for various paleo- 

 geographic models for the same time interval, and allowing for 

 effects on the planetary wind and current system of secular 



Fig. 7. Circumglobal biogeographical belts as defined by marine plankton 

 (mainly according to Steuer, 1933, as modified by Hedgpeth, 1957, p. 367). 



variations in the latitudinal distribution of heat (Brooks, 1949, 

 pp. 50-53), the paleobiogeographer could experimentally determine 

 which circulation pattern best satisfies known biotal distributions 

 and his climatic inferences. He can, of course, do the same thing 

 with a crayon on a globe, or with pencil and paper, but in any case 

 it is of value to check the dynamic details on experimental models. 

 Such an approach could greatly improve the basis of paleoclima- 

 tology and more effectively test the relative probability of apparent 

 polar wandering, continental drift, or stability of the outer crust 

 and continents at various times in the past. 



