Paper No. 186-7
Presentation Time: 9:00 AM-6:30 PM
SCLEROCHRONOLOGICAL STUDY ON AMMONOID JAWS
ROUGET, Isabelle, CR2P (SU-MNHN-CNRS), Sorbonne Université, 4 place Jussieu, Paris, 75005, France, KRUTA, Isabelle, Invertebrate paleontology, American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024-5192; CR2P (MNHH-SU-CNRS), Sorbonne Université, 4 place Jussieu, Paris, 75005, France, MOUCHI, Vincent, Laboratoire d’Ecogéochimie des Environnements Benthiques (LECOB UMR 8222), Observatoire Océanologique de Banyuls, Banyuls/Mer, F-66650, France, PAZZÉ, Léo, CR2P (MNHH-SU-CNRS), Sorbonne Université, 4 place Jussieu, Paris, 75005, France, DAUPHIN, Yannicke, Institut de Systématique, Evolution, Biodiversité (ISYEB), Museum National d’Histoire Naturelle, Centre National de la Recherche Scientifique, Ecole Pratique des Hautes Etudes, Sorbonne Université, Paris, 75005, SEGALEN, Loïc, Institut des Sciences de la Terre de Paris (iSTeP), Sorbonne Université, Centre National de la Recherche Scientifique : UMR7193, Paris, 75005, LANDMAN, Neil H., Division of Paleontology (Invertebrates), American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024-5192 and BAUMGARTNER, Lukas, Institute of Earth Sciences, University of Lausanne, Lausanne, CH-1015, Switzerland
Sclerochonological studies carried out on Recent and fossil mollusks provide a methodological framework that could be applied to ammonite lower jaws. As a challenge for macroevolutionary studies, age estimations based on growth features and chemical compositions of the low Sr aragonitic outer shell have been attempted on few exceptionally preserved specimens, but remain questionable. Compared to the aragonitic shell, the calcitic covering of the lower jaw (called aptychus) is poorly investigated although in Recent cephalopods, chitinous beaks are considered relevant proxies for the age of the animal.
Following these studies, well-preserved aptychi from the Campanian of Alabama (Mooreville Chalk) were investigated to assess their potential for sclerochonological studies. We analyzed growth lines spacing, microstructure, and variation of the chemical composition along the growth direction (∂18O) and trace elements. Microstructural observations indicate that fine growth features (up to 2 μm thick) are well preserved and that a part of paleobiological information is preserved.
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