Plate Tectonics and the Biogeography of the Cypraeidae (Mollusca: Gastropoda)

The distribution of living species of the Cypraeidae (Mollusca: Gastropoda) features two centres of species richness, one in the Western Pacific and the other in the west central Indian Ocean. Species richness declines from these two areas. By formulating a quantitative index of decrements in species richness from one biogeographic province to another, it is possible to test the effects of plate tectonics on the distribution of cypraeid species. Using a model developed by Valentine (1971), the data reveal significantly different biogeographic consequences of plate tectonic elements (ridges and subduction zones; F= 16 04, P < 0 005). The distribution of regional endemics and widespread species are consistent with this result. These data can also be used to infer the direction of migration from region to region. The distribution of higher levels of organization (tribes and sub-families) suggests that earlier lineages of the Cypraeidae dispersed through the Tethys corridor while more recent ones radiated widely in the IndoPacific after the suturing of Africa and Eurasia. Thus, the effects ofplate tectonics appear to be a major influence on the biogeography of the Cypraeidae. These data are compared to others in the literature, and some implications of them are discussed.