Ammonite survival across the Cretaceous–Paleogene boundary confirmed by new data from Denmark

We provide a reassessment of the hypothesis of ammonite survival across the Cretaceous–Paleogene (Maastrichtian–Danian) boundary, based on new data from the lower Danian Cerithium Limestone Member at Stevns Klint, eastern Denmark. The occurrence of this unit in disjunct basins between eroded crests of uppermost Maastrichtian bryozoan mounds prompts a reconsideration of ammonite redeposition as an alternative to the survival hypothesis. We describe new ammonite specimens from the Cerithium Limestone, representing the genera Hoploscaphites, Baculites and Fresvillia. In order to elucidate the nature of these fossils, we study their local depositional settings, based on detailed, chiefly taphonomic and sedimentological (microfacies) observations. Results for the main part of the Cerithium Limestone point to the autochthonous nature of the enclosed ammonites, which implies that they are Danian survivors. Only a single individual from the lowermost part of the Cerithium Limestone is considered a reworked Maastrichtian fossil. In summary, our results confirm ammonite survival into the Danian for the bulk of the Cerithium Limestone fauna, stimulating questions for further research of what actually killed the last ammonites that lived on Earth.