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Biogeosciences An interactive open-access journal of the European Geosciences Union
Journal topic
Volume 12, issue 23
Biogeosciences, 12, 6945–6954, 2015
https://doi.org/10.5194/bg-12-6945-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.
Biogeosciences, 12, 6945–6954, 2015
https://doi.org/10.5194/bg-12-6945-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 07 Dec 2015

Research article | 07 Dec 2015

Stable isotope study of a new chondrichthyan fauna (Kimmeridgian, Porrentruy, Swiss Jura): an unusual freshwater-influenced isotopic composition for the hybodont shark Asteracanthus

L. Leuzinger1,2,a, L. Kocsis3,4, J.-P. Billon-Bruyat2, S. Spezzaferri1, and T. Vennemann3 L. Leuzinger et al.
  • 1Département des Géosciences, Université de Fribourg, Chemin du Musée 6, 1700 Fribourg, Switzerland
  • 2Section d'archéologie et paléontologie, Office de la culture, République et Canton du Jura, Hôtel des Halles, 2900 Porrentruy, Switzerland
  • 3Institut des Dynamiques de la Surface Terrestre, Université de Lausanne, Quartier UNIL-Mouline, Bâtiment Géopolis, 1015 Lausanne, Switzerland
  • 4Universiti Brunei Darussalam, Faculty of Science, Geology Group, Jalan Tungku Link, BE 1410, Brunei Darussalam
  • anow at: CRILAR, 5301 Anillaco, La Rioja, Argentina

Abstract. Chondrichthyan teeth (sharks, rays, and chimaeras) are mineralized in isotopic equilibrium with the surrounding water, and parameters such as water temperature and salinity can be inferred from the oxygen isotopic composition (δ18Op) of their bioapatite. We analysed a new chondrichthyan assemblage, as well as teeth from bony fish (Pycnodontiformes). All specimens are from Kimmeridgian coastal marine deposits of the Swiss Jura (vicinity of Porrentruy, Ajoie district, NW Switzerland). While the overall faunal composition and the isotopic composition of bony fish are generally consistent with marine conditions, unusually low δ18Op values were measured for the hybodont shark Asteracanthus. These values are also lower compared to previously published data from older European Jurassic localities. Additional analyses on material from Solothurn (Kimmeridgian, NW Switzerland) also have comparable, low-18O isotopic compositions for Asteracanthus. The data are hence interpreted to represent a so far unique, freshwater-influenced isotopic composition for this shark that is classically considered a marine genus. While reproduction in freshwater or brackish realms is established for other hybodonts, a similar behaviour for \textit{Asteracanthus} is proposed here. Regular excursions into lower salinity waters can be linked to the age of the deposits and correspond to an ecological adaptation, most likely driven by the Kimmeridgian transgression and by the competition of the hybodont shark Asteracanthus with the rapidly diversifying neoselachians (modern sharks).

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We measured the oxygen isotopic composition of Late Jurassic chondrichthyan teeth (sharks, rays, chimaeras) from the Swiss Jura to get ecological information. The main finding is that the extinct shark Asteracanthus (Hybodontiformes) could inhabit reduced salinity areas, although previous studies on other European localities always resulted in a clear marine isotopic signal for this genus. We propose a mainly marine ecology coupled with excursions into areas of lower salinity in our study site.
We measured the oxygen isotopic composition of Late Jurassic chondrichthyan teeth (sharks, rays,...
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