Biogeography and Biogeographic History of Clypeasteroid Echinoids

Biogeographic patterns of clypeasteroid echinoids are established on the basis of geographic distribution of 110 extant species. Cluster analysis is applied to identify major biogeographic units, or bioprovinces. The patterns of endemism and species diversity (both latitudinal and longitudinal gradients) are entirely consistent with those observed in other marine shallow-water groups. The mosaic distribution of clypeasteroid species in the Indo-Pacific realm lends support to vicariance-and-refuge model for origination of high diversity foci in Indo-West Pacific and, by implication, Caribbean. Relationships among the modern clypeasteroid biogeographic units can be analysed in terms of a biogeographic cladogram. In order to increase informativeness of the cladogram, data on distribution of living clype- asteroid species are supplemented with information from the fossil record. The resulting biogeographic cladogram contains nevertheless several inconsistencies which can be only explained by secondary dispersal, either by secular migration, or diffusion, or even chance dispersal. We conclude that the biogeographic history of clypeasteroid echinoids is very complex, with both vicariance and secondary dispersal playing a considerable role. Moreover, it cannot be properly reconstructed without evidence from the fossil record. This implies that historical biogeography must remain largely narrative and pluralistic.