Biogeography of planktonic Foraminifera

7.7 Conclusions

There are several important unresolved issues in the area of modern planktonic foraminiferal biogeography. The large-scale latitudinally symmetrical faunal provinces do not appear to show a consistent relationship to comparably-scaled hydrographic features. The origins of these provinces are therefore likely to be understood by reference to other causal factors. The first of these is the degree to which smaller-scale hydrographic features such as current, gyre, and frontal systems combine to play a role in determining larger-scale latitudinal distribution patterns. The second is the role historical processes — particularly, latitude-dependent rates of speciation and extinction, and the development of tectonic barriers — have played in establishing faunal provinces and the global diversity gradient. A number of additional factors, including depth habitats, bipolarity, pore size, coiling direction, and iterative evolution, are indirectly related to physicochemical characteristics of the foraminiferal habitat.

As our understanding of the basic governing principles of modern foraminiferal biogeography develops, it becomes easier to interpret the fossil record in the light of those principles. By the same token, modern distribution patterns, since they are partly the result of historical processes, cannot be fully explained without reference to their past development. We are so accustomed to hearing that the present is the key to the past that we sometimes forget that the past can also be the key to understanding the present. It follows that biogeographic studies of modern and fossil Foraminifera must necessarily proceed hand-in-hand.