The “Vaginaten”: the dominant cephalopods of the Baltoscandian Mid Ordovician endocerid limestone

The lower part of the Baltoscandic Orthoceratite Limestone (Kunda Stage, Darriwilian) is characterized by abundant and often large orthoconic endocerid cephalopods. The endocerids of this limestone, known historically as the “Vaginaten”, are among the historically earliest figured Swedish fossils. The taxonomic history of the two most common and most characteristic of these endocerids is complicated by the use of wastebasket taxa and an extensive oversplitting. Here, the status of the name Anthoceras vaginatum (Schlotheim) is clarified for an annulated endocerid with high variability in ornamentation and conch form. The large, smooth Proterovaginoceras incognitum (Schröder) is the predominant endocerid of the lower parts of the Orthoceratite Limestone. Together, more than 90% of the cephalopods of the endocerid limestones can be assigned to these two species. Massive changes in the cephalopod composition throughout the Kunda Stage at Hälludden, Öland, Sweden, indicate significant changes in the ecosystem during this time interval. These changes were formerly unrecognized and coincide with drastic changes in conodont assemblages and benthic communities.