Some rare helical Ammonoidea from the lower Aptian (Lower Cretaceous) of the Paris Basin (NE France)

Abstract

In the present paper, we describe and figure some rare lower Aptian (Lower Cretaceous) helical ammonoids from the Deshayesites deshayesi Zone of the Argiles à Plicatules Formation (Paris Basin, NE France). Those are the only helical ammonoids known in this zone so far. They were only occasionally evoked in literature and this is probably on the basis of the specimens here described that, according to us, the genus Toxoceratoides (Helicancylidae) was wrongly regarded as possessing an early helical spiral part. We demonstrate here that these specimens are not belonging to Toxoceratoides nor Helicancylidae: they are interpreted as ‘abnormally’ helical representatives of the genus Ancyloceras (Ancyloceratidae) or a new taxon of Ancyloceratidae.