The evolution of certain upper Cretaceous hystrichospheres from South Africa

Abstract

This paper traces clearly, for the first time, an evolutionary sequence in dinoflagellate cysts. The sedimentary samples containing the cysts are from nnorthern Natal, South Africa, and are of Upper Cretaceous age. The genera concerned in this study are Exochosphaeridium Davey et al. (1966), Cordosphaeridium Eisenack (1963b) and an intermediary genus Amphorosphaeridium nov. Morphological changes exhibited by the cysts are related to ecological considerations and are shown to be directional; their stratigraphic usefulness is also discussed. In all one genus, three species and two varieties are erected.