PhD Defense - Clément Jauvion

From life to stone : exceptional preservation of fossil marine arthropods

Thèse de doctorat sous la direction de Sylvain Charbonnier et de Sylvain Bernard

Composition du jury :

• Mme Emmanuelle Vennin, Pr Université de Bourgogne, rapporteuse
• M. Arnaud Brayard, CR CNRS, rapporteur
• Mme Laure Corbari, MC MNHN, Examinatrice
• Mme Elise Nardin, CR CNRS, examinatrice
• Mme Isabelle Rouget, Pr MNHN, examinatrice
• M. Jean Vannier, DR CNRS, examinateur
• M. Sylvain Charbonnier, Pr MNHN, directeur de thèse
• M. Sylvain Bernard, CR CNRS, directeur de thèse

Abstract:

The fossil record is incomplete and does not really account for ancient biodiversity. Some exceptionally well-preserved deposits are rich in “soft” organisms that are rarely fossilized. X-ray tomography has revealed remarkable biological structures (eggs, internal organs) allowing us, for example, to reconstruct reproductive traits in Polychelida (Decapoda) from the Jurassic site of La Voulte-sur-Rhône. As the causes of such preservation are still poorly known, in situ analyses of the mineralogical composition of fossil arthropods have enabled us to reconstruct the fossilization processes at the same site and at a Cretaceous site in Lebanon. We thus show that biodegradation is essential in fossilization, and that the mode of preservation is explained by the precipitation around the fossil of a concretion (volume fossils) or not (flat fossils). We discuss the effect of microenvironments and associated microorganisms.