An 'Elvis' echinoid, Nucleopygus (Jolyclypus) jolyi, from the Cenomanian of France: phylogenetic analysis, sexual dimorphism and neotype designation

Newly collected specimens of an uncommon and poorly known irregular echinoid, Nucleopygus (Jolyclypus) jolyi, are recorded from Cenomanian strata in Charentes (western France). The first examples of this echinoid to have been described date back to the late nineteenth century; those specimens (i.e., the types) appear to have been lost. What particularly distinguishes this taxon from other Cenomanian echinoids is the singular combination of derived and plesiomorphic morphological characters, the latter being reminiscent of Jurassic irregular echinoids. Derived features concern the appendages, employed in locomotion and feeding, whereas ancestral characters involve the apical system and periproct. This peculiarity has led previous workers to include this echinoid in the stem-group Galeropygidae, which would imply a >40-myr gap in the stratigraphic range of this group or, alternatively, challenge the stratigraphic provenance of the taxon. A detailed examination of newly collected material has now allowed us to resolve the apparent discrepancies, describe a reversal and document sexual dimorphism as well. A phylogenetic analysis was carried out in order to revise the systematic position of the taxon, now transferred to the Cretaceous genus Nucleopygus. A neotype is designated.