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RESEARCH PRODUCT

Hettangian ammonites from the old iron mine of Beauregard (Thoste, Côte-d’Or, France).

subject

description

The ammonite fauna of the old iron mine of Beauregard is reviewed. Only nine specimens from this locality are presently known. They are housed in the collections of the “Musée de Semur-en-Auxois”, of the “Muséum national d’Histoire naturelle” (Paris) and of the “Ecole Nationale Supérieuredes Mines” (Claude Bernard University, Lyon 1). The age, or possibly the ages, of these ammonites remain to precise in a coarsely defined time-span including the upper part of the early Hettangian and the middle Hettangian (pro parte?). These fossils, usually finely preserved, were collected during the nineteenth century thanks to intensive mining in the Thoste-Beauregard area. They are illustrated uniformly to facilitate comparisons between the different taxa. A new genus (i.e., Lepteocaloceras n. gen.) and two new species (i.e., L. evrardii n. sp. et L. ? strictum n. sp.) are described. Despite a small number of spécimens (only nine) but with four distinct species and two related forms, left in open nomenclature, this fauna is clearly highly diversified in taxonomic terms. It is so peculiar that it is difficult, or impossible, to propose any convincing affinities with NWE European or even Tethyan taxa. The statigraphic and palaeobiogeographic frameworks remain poorly understood. This peculiar faunal assemblage can suggest an endemic pattern and/or adaptations to marginal environment for ammonites. Unfortunately, and without accurate stratigraphic constraints, such assumptions renmain speculative and nothing more than working hypotheses.