PELTOCERATINAE (AMMONOIDEA) OF THE TREZEENSE SUBZONE (ATHLETA ZONE, UPPER CALLOVIAN) IN COTE DOR (FRANCE)

Many populations of Peltoceratinae from the Trezeense Subzone of the C ote d'Or and considered as synchronous, are studied as a single paleob iological unit. Morphological and biometrical study of ontogeny identi fies four groups that can be explained by sexual dimorphism. These gro ups comprise two morphs, each including a microconch and a macroconch. The systematics of Peltoceratinae from the Trezeense subzone is revis ed and simplified to with a single species. The morphs, always found t ogether, show quantitative differences in distribution related to pale odepth. This polymorphism is associated with the Upper Callovian trans gression when the Peltoceratinae invaded new environments.