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RESEARCH PRODUCT

Les Oppeliidae (Ammonitina) de l'horizon à Collotiformis (Callovien supérieur, zone à Athleta) de la région dijonnaise (Côte-d'Or, France)

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Abstract In the Dijon area, the top of the Athleta zone contains rich ammonite fauna dominated quantitatively by two families: Perisphinctidae and Oppeliidae. The Oppeliidae are diversified and make up a numerically larger proportion of the ammonite fauna than in the underlying strata (up to 57 %). The exceptional state of preservation of the ammonites has permitted a precise study to be made of ontogenesis and intraspecific variability. Four sub-families are found (Oppeliinae, Hecticoceratinae, Distichoceratinae and Taramelliceratinae), within which sexual dimorphs have been recognised. One small form, characterized by lappets and a body chamber with ellipticoidal-trending coiling, is interpreted as the microconch dimorph of the Paralcidia genus which was unknown until now. One specimen of Creniceras , the oldest collected in Cote-d'Or, can be interpreted as the microconch dimorph of Taramelliceras .