Approach to Paleobiodiversity: Mesozoic Calcareous Nannoplankton: Preface

Abstract

“ La Terre est bleue comme une orange ” — Paul Eluard, 1929, L’amour la Poesie The coccolithophorids are truly exceptional life forms. The smallest organisms able to secrete a skeleton, they have opted for biological complexity and ecological flexibilty, and seem to have ensured their destiny as vital participants in the most fundamental processes that regulate the earth system. Their unique cell surrounds itself with an exoskeleton (coccosphere) of calcium carbonate (mostly calcite, but also aragonite in some instances) precipitated in the form of tiny platelets (coccoliths), some with incomparably delicate morphology, others with remarkably complex structure. With alternately motile (biflagellate) and non-motile phases, most species produce such vastly dissimilar coccoliths during their life cycle that it has taken exactly 100 years to recognize this taxonomic deceit. As the cells proceed from the haploid to the diploid phase they acquire the ability to practice intracellular calcification, organizing rings of flattened rhombohedrons into a finite number of distinctive morphostructures. Like so many Ariadne’s threads, and with the recent assistance of molecular biology, these structures trace the phylogenetic evolution of the group since its origin ~225 Ma in the late Triassic Tethyan Ocean. As primary producers, the coccolithophorids inhabit the photic zone of the ocean, organizing themselves in vertical strata and along latitudinal belts. A distinct deep dwelling community thrives between 150 and 200m depth, while the upper photic zone (0 to 50m) has its particular adepts. Most diversified in the oligotrophic oceanic gyres, coccolithophorids are most productive in the mesotrophic waters of regions of upwellings and …