Eighty years of chitinozoan research: From Alfred Eisenack to Florentin Paris

Highlights

• We review the research on Chitinozoa since their first description in the 1930s.

• Chitinozoa (or “chitinozoans”) became a major microfossil group in the Palaeozoic.

• Original studies, including the creation of the name, date back to Alfred Eisenack.

• Most modern studies, since the 1970s, have been coordinated by Florentin Paris.

Abstract

In the early 1930s Alfred Eisenack first reported unknown, bottle-shaped, organic-walled microfossils that he had discovered in erratic boulders from the south-eastern shores of the Baltic Sea. Eisenack erected the new group Chitinozoa to classify these strange microfossils of unknown biological affinity. From the 1930s to the 1950s, a few publications appeared reporting new findings and providing descriptions of these fossil organisms. It was only since the 1960s, with the development of the oil industry and the intensive biostratigraphical use of organic-walled microfossils, that publications dealing with chitinozoans became more numerous and that the description of new genera and species rapidly increased. The peak of description of new species was reached in the 1960s, but the number of publications remained high into the late 1990s. Since the 1990s the research activities on chitinozoans are conducted by a much smaller number of scientists. One of the major driving forces of chitinozoan research in the last forty years was Florentin Paris at the University of Rennes (Brittany, France). He first established a high-resolution chitinozoan biostratigraphy of the Ordovician of southern Europe and played an active role in bringing all scientists together for the development of global biostratigraphical schemes and palaeobiogeographical scenarios of the Ordovician, Silurian and Devonian. It was also Florentin Paris, together with his Estonian colleague Jaak Nõlvak, who suggested the now widely accepted biological interpretation that Chitinozoa are most probably egg cases of a planktonic organism unknown from the fossil record. F. Paris was also the first to collaborate with experts to use biogeochemical analyses and the C isotope signal of the chitinozoans to better understand their biological affinity and detect biogeochemical changes in Palaeozoic oceans.

Introduction

Alongside the acritarchs (generally related to phytoplanktonic organisms), the spores and pollen grains (related to land-plants) and the scolecodonts (elements of the jaws of polychaetes), the chitinozoans are considered today as one of the major groups of the Palaeozoic organic-walled microfossils (palynomorphs). The group was first discovered and described some 80 years ago by Eisenack (1930), who proposed the name Chitinozoa for these bottle- or urn-shaped organic microfossils. Since the 1960s the chitinozoans have become very important in biostratigraphy, and today they are widely considered as one of the major groups providing solid biostratigraphical correlations at local, regional and global scales, with a similar or, in some intervals, even more precise resolution than that of the graptolites and conodonts, considered as the two ‘classical’ biostratigraphic fossil groups of the Ordovician, Silurian and Devonian. In addition, chitinozoans have the advantage that they can be easily found in both limestones and mudstones, unlike graptolites and conodonts, respectively.

During the last 40 years, Florentin Paris, ‘Directeur de Recherches’ at the Centre National de la Recherche Scientifique (CNRS) at the University of Rennes (Brittany, France), was the driving force behind chitinozoan research. He contributed to all aspects of chitinozoan investigations: taxonomy, biostratigraphy, palaeobiogeography, palaeoecology, palaeobiodiversity and biogeochemistry. The stratigraphical information provided by his work proved to be crucial for the understanding of regional geology and palaeobiogeography, first of all of Brittany, but later of the entire Armorican Terrane Assemblage, southern Europe and most areas of the ‘northern Gondwana domain’.

This paper attempts to outline the main trends in chitinozoan research of the last 80 years, i.e. since the pioneering work by Alfred Eisenack in the early 1930s to the standards reached at the beginning of the 21st century. We do not attempt to provide an exhaustive list of all the chitinozoan papers that have been published since 1930; readers are invited to consult the listed bibliography to find the references not cited herein. Because Florentin Paris was one of the major actors in chitinozoan research during the last 40 years, this review will inevitably highlight his contribution during that period. This review paper is the first of a set of papers of a special issue on Palaeozoic marine palynomorphs respectfully dedicated to Florentin Paris.