The Deshayesitidae (Ammonoidea, Ancyloceratina) in the lower Aptian (Lower Cretaceous) of the Les Ferres Aptian Basin (southeastern France)

Abstract

In the present work, we study 335 specimens of Deshayesitidae (Ammonoidea) from the vicinity of the village of Les Ferres (SE France). The Deshayesitidae is the current key family for the ammonite biostratigraphy of the lower Aptian (Lower Cretaceous). Despite poorly preserved, the studied material could have been identified at species rank in most cases and allowed establishing the biostratigraphic frame of the lower Aptian of the study area. The results are as follows: (1) the studied samples range from the Deshayesites forbesi Zone to the Dufrenoyia furcata Zone; (2) their ontogenetic sequence is described; (3) their evolutionary patterns are consistent with those observed in other samples of Deshayesitidae; (4) no dimorphism is conspicuous; (5) the identified taxa are, from earliest to latest: Deshayesites sp. (Deshayesites forbesi Zone, rounded ventral area probably without smooth siphonal band), Deshayesites multicostatus Swinnerton, 1935 (index of subzone, intermediate smooth siphonal band then rounded ventral area), Deshayesites grandis Spath, 1930 (index of subzone, longer smooth siphonal band then subtabulate ventral area on phragmocone), Dufrenoyia furcata (J. de C. Sowerby, 1836) (index of subzone and zone, even longer smooth siphonal band then subtabulate ventral area, onset of rounded to claviform latero-ventral tubercles in inner whorls) and Dufrenoyia dufrenoyi (Orbigny, 1841) (index of subzone, even more longer smooth siphonal band, latero-ventral tubercles claviform only).