Preservation of soft-bodied xylophagous mollusks (Bivalva, Teredinidae) and evolutive implications
Résumé
Teredinidae are obligate xylophagous bivalves colonizing drifted woods, which display a very specialized anatomy with valves highly reduced in size. In addition to the shell, the animals secret terminal aragonitic structures (pallets) and calcitic linings, but the vast majority of their anatomy consists in soft-tissues. Therefore, their fossil occurrences mostly correspond to burrows more or less infilled by sediments and to isolated valves and pallets. Here, we report exceptionally preserved teredinid bivalves from the Early Cretaceous of the Envigne Valley (Vienne, France) with soft parts emerging out of the wood (e.g. foot), like frozen by silicification. This superficial preservation of the mollusks led us to investigate the inner content of the two inhabited woody pieces. These specimens were thus scanned using classical computed tomography in order to document the anatomical preservation and the animals’ organization in the woods. The 3D reconstructions evidenced that fragile soft-tissues were preserved inside like the mantle or the respiratory siphons, but also surprisingly that their mineralized pallets, which are a key-feature of the Teredinidae anatomy, were absent. That led us to try analyzing further the preserved morphological details of these early shipworms to give insights on the morphological evolution of the pallets among this taxon.
Origine : Fichiers produits par l'(les) auteur(s)