A water depth model for the evolution of the planktonic Foraminiferida

Abstract

Recent papers on the evolution of the planktonic Foraminiferida have stressed the importance of repeated patterns^1,2 in the Neogene and Palaeogene, as well as in the Cretaceous^1–4. Most authors have recognized the importance of gross morphological characters (the biocharacters of Steineck and Fleischer²) and used them to illustrate the evolution of the superfamily Glo-bigerinacea, as well as a prime tool in classification. Cifelli¹ and Frerichs⁴ relate such patterns of evolution to the available palaeotemperature data⁵, and while temperature is clearly important I shall show that it is not the complete story. Here the evolution of the planktonic Foraminiferida is reconsidered in the light of recent advances in the understanding of distributional controls of the modern fauna. I suggest that well-known ‘iterative’ trends indicate successive attempts at colonizing deeper levels in the water column.