ABSTRACT
Studies of modern biogeography have clarified the distribution of many taxa of all ranks, establishing provinces and the types of barriers between them. Palaeobiogeography has permitted the recognition of ancient oceans and island complexes, together with a range of land areas from micro to supercontinents. If the migrant population is now isolated from its parent gene pool, evolution will probably proceed differently from that in the parent population and both morphological and ecological shifts are likely. Valentine drew attention to a range of plate tectonic settings, including the evolution of spreading ridges, island arcs, subduction and transform zones, that may influence biological distributions. It is now recognized that in most cases provinciality develops through continental fragmentation and the controls of climatic or temperature gradients. This radiation during the last few million years more than compensated for any extinctions in these marine faunas. Islands, however, have also provided models for the migration patterns, diversification and eventual extinction of biotas.
