Morphologie, fonction et évolution de quelques grains de pollen normapolles du Crétacé supérieur

Upper Cretaceous pollen grains with a thick wall (exine) and sometimes protruding apertures, included in the Normapolles Pflug, are considered from a functional point of view. Because of the high development of compression-resistance features correlative with a high protection of the gametophyte, an entomophilic phase is supposed in the dissemination of some types, but anemophily appears to have been a developmental trend of apertural specialization for others. As these functional features are characteristic of the outer part of the wall (the sexine), the tetrahedral morphology of the inner part (the nexine) and the lack of evidence that it influenced the whole adaptive system suggest that angiospermic constraints have acted first at a pteridophytic stage.