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| Titel |
Stable isotope study of a new chondrichthyan fauna (Kimmeridgian, Porrentruy, Swiss Jura): an unusual freshwater-influenced isotopic composition for the hybodont shark Asteracanthus |
| VerfasserIn |
L. Leuzinger, L. Kocsis, J.-P. Billon-Bruyat, S. Spezzaferri, T. Vennemann |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 12, no. 23 ; Nr. 12, no. 23 (2015-12-07), S.6945-6954 |
| Datensatznummer |
250118192
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| Publikation (Nr.) |
 copernicus.org/bg-12-6945-2015.pdf |
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| Zusammenfassung |
| 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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