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At the end of the Devonian, several profound extinctions affected a large number of marine groups. However, some of them, such as holocephalan chondrichtyans, showed a great diversification during the recovery of the ecosystems, during the Tournaisian. Despite the fact that a large taxic diversity has been documented for these holocephalans; their ecological diversity is however poorly known, because the shape of isolated teeth can be a poor predictor of the ecology of these animals. Microwear analysis has the potential to reveal distinct diets and actual use of teeth in these extinct animals during the Tournaisian. We analysed the microwear of Tournaisian holocephalans from the Tournai and Ourthe formations of Belgium. Dental microwears were observed qualitatively on 20 teeth with a scanning electron microscope and mapped and analysed in detail for 7 of them with ArcMap software. While pits are almost totally absent in our sample, our microwear dataset revealed two populations of scratches with distinct length distributions. We suggest that these populations were produced by two different mechanisms. The first population contains mainly long scratches (>0.2 mm, up to 2.0 mm) that are often oriented 40° to 70° compared to the anteroposterior axis of the tooth. We propose that these scratches would have been produced by trituration. The second population comprises almost exclusively of short scratches (<0.2 mm) especially abundant on the mesial face of the teeth and preferentially oriented subparallel to the anteroposterior axis. They would have been produced when the holocephalans dug into sea bottom sediments while searching for food. To identify materials that might have caused the observed microwear, we compared the hardness of the holocephalan orthodentine, making the bulk of the crown of holocephalan teeth, and materials present in their environment. The skeleton of a wide series of marine organisms (crinoids, brachiopods, molluscs) is composed of calcite or aragonite, which appears to be slightly harder than holocephalan orthodentine. These materials may thus scratch holocephalan teeth but are hardly able to produce pits because of the small difference in hardness. Tournaisian holocephalans were thus probably feeding on benthic faunae and they likely dug in the sediment at the search of food. If correct, this might rule out prey items located clearly above the sea floor, such as ammonioids or high-stalked crinoids. However, most of our specimens showed similar microwear features, which prevents us to highlight ecological differences between the taxa we sampled.

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Autor(es)

Demoulin, Catherine -  Derycke, Claire -  Michel, Christian -  Fischer, Valentin - 

Id.: 71080710

Idioma: inglés  - 

Versión: 1.0

Estado: Final

Cobertura:  international - 

Tipo de recurso: info:eu-repo/semantics/lecture  - 

Tipo de Interactividad: Expositivo

Nivel de Interactividad: muy bajo

Audiencia: Estudiante  -  Profesor  -  Autor  - 

Estructura: Atomic

Coste: no

Copyright: sí

Requerimientos técnicos:  Browser: Any - 

Relación: [References] PPMB meeting 2017, Liège, Belgium (08/12/2017)

Fecha de contribución: 13-mar-2018

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