Lower Cretaceous Crato clay samples revisited: some new results from scanning electron microscope investigations of Afropollis pollen

Abstract

This article presents re-investigated Crato Formation sample material from David J. Batten’s palynological legacy using a combination of light microscopy (LM) and scanning electron microscopy (SEM). The investigation shows that Afropollis jardinus specimens from Crato clay have central bodies that are either smaller (36%) or larger (42%) than half the diameter of the entire body or are lost (22%), probably due to preservational reasons. All grains display the same grading of the reticulum, in which the size of the brochi decreases from the proximal to the distal pole. This observation only was possible because no cover slips were used during LM observation and therefore the individual grains could be turned and moved with a micro-manipulator. Detailed SEM observations revealed that the height of the muri and the height of the always present granular infrastructure of the reticulate sexine generally increase from the distal to the proximal pole. On five of 19 specimens (plus a lump of four) investigated with SEM an ulcerate aperture can be observed on the distal pole, located within the smallest brochi of the reticulum, and three other specimens show a faint ulcerate aperture in the same location. The area with small the smallest brochi and the ulcus are restricted to the distal pole. This ulcerate aperture cannot be seen using only LM. The geologically older Afropollis operculatus and A. zonatus are characterised by operculate and ring-like apertures, therefore the ulcus in A. jardinus must be a derived type and is probably a result of convergent evolution.