Mature modifications and sexual dimorphism in Turrilitidae (heteromorph ammonites): contribution of remarkable Mariella bergeri specimens (upper Albian, southeastern France)
Résumé
In ammonites, the identification of mature shells is the logical but not naturally simple prerequisite to determine sexual dimorphism. Here, we provide elements suggesting sexual dimorphism in the upper Albian Mariella bergeri species (Turrilitidae), based on three specimens with preserved adult peristome from the Clansayes locality (southeastern France). We compare the morphology of the terminal peristomes observed in M. bergeri with that of the few other known examples in Turrilitidae. In turn, we hypothesize that upper Albian Mariella (e.g., M. bergeri), lower Cenomanian Mariella (e.g., M. oehlerti) and lower Cenomanian Hypoturrilites (e.g., H. gravesianus) share the same peristome morphology. The observed similarities seem to support the close relationships between these three genera inferred from the most recent phylogeny of the family Turrilitidae. Conversely, the Cretaceous Research 2 2 peristome morphology of upper Albian Turrilitoides appears markedly different. Finally, it is unclear how the shape of the adult peristome of upper Albian Ostlingoceras (e.g., O. puzosianum) and middle Cenomanian Turrilites (e.g., T. costatus) can be related to the evolutionary lineages among Turrilitidae. To further increase our knowledge on the differences in peristome morphologies among Turrilitidae, more complete and remarkably preserved specimens of various genera are needed.
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