PALEOGEOGRAPHIC CONSTRAINTS ON BIOGEOGRAPHIC PATHWAYS

Paleogeographic maps provide the spatial context for understanding, interpreting and analyzing biogeographic patterns. A paleogeographic map, itself, is highly interpretive. On a global scale, a paleogeographic map must first represent the past positions of the continents and oceans according to the evidence from plate tectonics and paleomagnetism. However, this alone is not sufficient. Once the global plate tectonic framework has been established, a paleogeographic map must then illustrate the ancient distribution of highlands, lowlands, shallow seas, and deep ocean basins. This is done by reconstructing the changes in topography and bathymetry caused by tectonic and erosional processes. Young tectonic features, such as recent uplifts or volcanic eruptions, must be removed or reduced in size, whereas older tectonic features, such as ancient mountain ranges, must be restored to their former extent. As an example, ocean floor which subsides as it cools and moves away from a spreading ridge must be "unsubsided" or restored to its former depths. Once the ancient paleogeography is recreated, it is then possible to begin to model other global processes such paleoclimatic change, paleoceanographic circulation patterns, or changing biogeographic pathways.

At the turn of the twentieth century, the unsuccessful attempts to explain ancient biogeographic patterns using modern geography were, in part, responsible for the formulation and acceptance of continental drift. At the turn of the twenty-first century, we are now poised to apply advances in plate tectonics, paleoclimatic modeling and paleoceanic circulation to produce a comprehensive set of paleogeographic maps that can be used to unravel some of the complex patterns of Phanerozoic biogeographic change. In this presentation a new set of 3D paleogeographic maps will be presented for the Phanerozoic and late Precambrian.