Taxonomic Re-Examination of the Late Cretaceous Planktonic Foraminiferal Species Archaeoglobigerina Cretacea (d'Orbigny, 1840) and Constraints on Its Morphologic Variability and Stratigraphic Distribution in One of The Type Localities (Kent, SE England)
Résumé
ABSTRACT Distinctive and taxonomically relevant morphological differences exist between the original drawings of Archaeoglobigerina cretacea illustrated by d'Orbigny (1840) and the lectotype designated by Banner & Blow (1960), particularly regarding the equatorial periphery, which is rounded in the former and double-keeled in the latter specimen. Such differences would suggest that they are not conspecific, but this hypothesis cannot be easily tested because d'Orbigny's drawings likely represent a synthesis of observations on several specimens rather than a single individual and the slide intended to contain the lectotype is empty. In this study, we have re-examined the A. cretacea type specimens deposited in the d'Orbigny collection at the Muséum National d'Histoire Naturelle in Paris and samples from one of the type localities (Kent, SE England) with the aim to reconstruct d'Orbigny's species concept, clarify its morphological features, and better constrain its stratigraphic distribution. Our study suggests that d'Orbigny's concept for A. cretacea was broad and included unkeeled as well as double-keeled morphotypes. However, assemblages from Kent yield common and large-sized specimens conspecific with the lectotype in the middle Santonian-lower Campanian, while morphotypes resembling the drawings of d'Orbigny are absent. Accordingly, five topotype specimens from the lower Campanian of Kent are herein illustrated in order to stabilize the species concept adopted over the last 60 years on the basis of the lectotype drawing and description. All topotypes possess a wide imperforate peripheral band and a moderately to weakly developed double-keeled periphery. Finally, the description of A. cretacea is emended to exclude specimens that do not possess an imperforate peripheral band and to include those that show curved and weakly beaded spiral sutures.