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Conference Papers Year : 2016

Echinoderms of the cretaceous deposits from Le Mans (France) : outstanding preservation conditions for an outstanding fauna

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Abstract

The Cenomanian stage of the geological time scale was named for Cenomanum, the Latin name of Le Mans (Sarthe, France). D’Orbigny (1847) has chosen the locality of Le Mans as a type area for its outstanding richness in marine fossils, especially molluscs, bryozoans, brachiopods and echinoderms. The Gueranger collection, at the Musée Vert (Le Mans) houses a unique echinoderm fauna, including many taxa unknown elsewhere. Preservation is exceptional with the occurrence of echinoids with still-attached spines (Tetragramma roissyi), starfish body fossils with plates, spines, and granules, still looking as in living conditions (Cenomanaster cenomanensis, Tethyaster guerangeri, Alkaidia sp.), two forms of ophiuroids (Ophiotitanos sp., an unpublished taxon) and Crinoids (“Isocrinus” cenomanensis) known from articulated bodies. All specimens were found in the so-called “lentilles à Echinodermes” of the “Sables du Mans” Formation. The sedimentary matrix usually combines clay and sand. Juignet (1974) recognized shallow marine conditions for the formation, with evidence of tidal currents. Individuals were buried rapidly and coated with clays brought by River floods, which favoured the preservation. The contrasted ecologies of the associated taxa suggest some mixing of individuals from distinct, not necessarily distant, environments, and the transport of bodies by coastal and/or storms currents. Similar preservation conditions are reported in the literature for other uncommon fossil sites that sample uncommon echinoderm faunas. The Cenomanian is a critical time for understanding of Asteroida and Ophiuroida. Their fossil record remains sparsely and unevenly distributed in time and space during the Early Cretaceous. A high diversity emerged in the Cenomanian of Europe at the dawn of Chalk age. The varied fauna described in the Chalk of Anglo-Paris basin, the North Aquitaine margin, German-Polish basin, and the Elbe valley, all show a high endemicity. The European fauna homogenize later with extension of the chalk and migration of lineages.
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Dates and versions

insu-01471976 , version 1 (20-02-2017)

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  • HAL Id : insu-01471976 , version 1

Cite

Loïc Villier, Gérard Breton, Delphine Desmares, John W.M. Jagt, Nicolas Morel, et al.. Echinoderms of the cretaceous deposits from Le Mans (France) : outstanding preservation conditions for an outstanding fauna. Colloque Cénomanien du Groupe Français du Crétacé, Musée Vert, Apr 2016, Le Mans, France. pp.89. ⟨insu-01471976⟩
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