Paleoblogeography of the Marine Realm* 



PRESTON E. CLOUD, JR. 



United States Geological Survey, Washington, D. C. 



In studying the geographical distribution of organized 

 beings philosophically, it is absolutely necessary to call 

 in the aid of geology. — ^Edward Forbes and Robert 

 Godwin-Austen (1859, p. 9). 



The picture cannot be painted in black and white when 

 nature has neither, but only infinite gradations of 

 darker and lighter gray. — George Gaylord Simpson 

 (1952, p. 164). 



THE ultimate aim of biogeography is to express and interpret the 

 dispersal of the individual components of the biosphere through 

 the filter systems of physical geography and environment and 

 their organization into distinctive, areally limited communities, 

 provinces, and realms. 



It is self-evident that, in order to survive as more than an 

 ecologic or evolutionary curiosity, a species must be able to 

 migrate, to install itself in new locations, to mature and reproduce 

 there, and to adapt itself to local conditions of existence over a 

 sustained interval of time. The degree to which different organisms 

 do this summarizes the ecologic vitality of the species and is the 

 best measure of success in the basic competition of all life for a 

 larger measure of the total energy supply. The patterns created 

 in the struggle for perpetuity are the essence of descriptive bio- 

 geography and paleobiogeography, which necessarily precede all 

 useful efforts toward interpretation. 



* Publication authorized by the Director, U.S. Geological Survey. 



This paper was critically read by W. P. Woodring, A. R. Palmer, W. A. Oliver, Jr., 

 R. S. Boardman, and F. M. Bayer. It was typed and checked for editorial con- 

 sistency and citation of references by Doris Low. Illustrations were drafted by 

 Elinor Stromberg, except for Fig. 5, which was drawn by Kathryn H. Karlson. 



151 



