PALEOBIOGEOGRAPHY OF THE MARINE REALM 



157 



incrfosin q solinity ond pH (obove normal), turbidity , CO 2 



decreosinq solinity ond pH (below normal), photosynthesis , oxygen, nutrients 



HADAL.ABYSSAL, BATHYAL ,/ SHELF 



LITTORAL } 



6000 4000 



y^SHALLOW or SHELF^v — SHORE ■ 



-APHOTIC- 



( Bathymetric 

 temperature 

 zones) 

 PSYCHROSPHERE 



(stratosphere) ^^^.---''^ 



THERMOSPHERE 

 (troposphere) 



e?.t^ 



^o; 



t^; 



^t 



s^^ 



r:?^ 



INFAUNA (climotic ond depth) 



Local variables 

 (excluding substrate) 

 Modern depth zores 

 (light, T, P, topography) 



Paleobiogeogrophi; 

 depth zones 



Light zones 



POLAR (FRIGID) • 



• SUBPOLAR (COLD) ■ 



SUBTROPICAL (WARMl- 



TTOPICAL_ 

 "(TORRID) 



•COLD 



Modern 



latitudinal 



climatic zones 



( Temperature range 

 of surface water ) 



PaleobiogeographK 

 climatic zones 



Fig. 3. Principal external variables affecting the distribution of marine biotas. 



three kinds: external, Internal, and cobiotic. External factors are 

 those of the physical and chemical environment; Internal factors 

 are those that exist within, and are an Integral part of, the organism 

 Itself; and cobiotic factors are those Introduced by the rest of the 

 contiguous biosphere, Including that part of the biosphere which 

 may live within, consume, or destroy the dead remains of the 

 organism In question. The response of the organism to these 

 variables Is expressed In Its adaptive and competitive character- 

 istics and ultimately In Its range In environment, space, and time. 

 The blotal composition of a given area or habitat at a given time 

 Is a composite function of metabolic Intensity and rate of evolution 

 (e.g., Bray and White, 1954, pp. 83-84), duration of biota and 

 environment (e.g., Fischer, 1960, p. 80), and Intrinsic charac- 

 teristics of environments and organisms. The limiting conditions 

 of existence for a particular species at a given place may Involve 

 any of those obtaining at the time of, or before, Its existence. The 



