ORIGIN AND EVOLUTION OF THE BIOTA OF SOUTHEASTERN NORTH AMERICA: EVIDENCE FROM THE FOSSIL PLANT RECORD

Abstract

The biota of southeastern United States is a complicated assemblage of plant and animal communities. Some species are presumably derivatives of the original Mesozoic vegetation that developed in the Appalachian highlands, while others were introduced later, as conditions became favorable for their migration and establishment. In this presentation an attempt will be made to characterize the older plant communities, and the conditions under which they evolved, and to demonstrate the existence of paleoenvironments suitable for the introduction of other components during subsequent periods of geologic time. Consideration will be given primarily to the angiosperms, which first become abundant in eastern United States during the Cretaceous Period. This limits discussion to Late Mesozoic and Cenozoic vegetation, and only brief attention will be given to the plant communities of the Early Mesozoic and Paleozoic eras. The plants of these older periods belong mostly to extinct families and genera, and provide little direct evidence for interpreting the origin and evolution of the modern biota. As far as possible, emphasis will be placed on new data provided by pollen and spore studies, and certain geochemical and geophysical techniques currently being used to study past environments. This tends to minimize dependence on the older, and in some cases questionable, paleontological data.