Oligocene basking sharks (Lamniformes, Cetorhinidae) of the Carpathian Basin with a reconsideration of the role of gill rakers in species diagnostics

Basking sharks are presented in the modern fauna by a single species (Cetorhinus maximus), although they have been much more diverse past. This group of first appeared fossil record middle Eocene Antarctic and U.S.A., but most described extinct taxa known from Oligocene lower Miocene Europe. Gill rakers abundant among basking shark remains their morphological details play an important role diagnostics. The shape isolated gill 16 localities Poland was analyzed using various approaches, including geometric morphometrics. Results indicate that descriptive characters wide range variation low diagnostic value, associated directly with position on arch. Morphological indices describe proportions discrete structures could be effective only identification stratigraphically distant taxa. Geometric morphometrics revealed significant differences between all designated earlier except for †Caucasochasma zherikhini †Keasius parvus. At same time, considering obtained results morphology along geographic distance, should assigned to †K. supports taxonomic distinctness both rhenanus septemtrionalis. Study reliable attribution rakers, absence other skeletal elements (teeth and/or vertebrae), sample-based multivariate approaches.