Morphology and ultrastructure of elater-bearing pollen from the Albian to Cenomanian of Brazil and Ecuador: implications for botanical affinity

Abstract

The morphological range of elaterate pollen grains is reassessed on the basis of detailed light, scanning electron and transmission electron microscope analyses of representatives from upper Albian–Cenomanian sections in Brazil and Ecuador. Included in the elaterate complex are Alaticolpites, Elaterocolpites, Elateroplicites, Elateropollenites, Elaterosporites, Galeacornea, Pentapsis, Regalipollenites, Senegalosporites and Sofrepites. All possess elater-like protuberances, but are otherwise morphologically disparate. Ultrastructural analyses of three taxa, Elateroplicites africaensis, Elaterosporites klaszii and Sofrepites legouxiae, reveals granular-alveolate ektexine and wall organization comparable to that of gnetalean pollen and to fossil Equisetosporites/ Ephedripites. A correlation exists between diversity/frequency levels of Elaterates and successive events in opening of the northern part of the South Atlantic Ocean. This is interpreted to reflect rapid diversification of the gnetalean sources of elaterate pollen in response to climatic perturbations associated with opening and enlargement of this ocean. The introduction and diversification of Elaterates coincides with early phases of angiosperm diversification, whereas extinction of the Elaterates-producing gnetalean group at the close of the Cenomanian heralded the rise to dominance of angiosperms in low latitudinal areas fringing the northern South Atlantic.