Acta Musei Moraviae

Addenda to the ammonite association of the Štramberk Limestone (J/K boundary, Outer Western Carpathians)

This paper presents a taxonomic study of a small collection of Jurassic/Cretaceous ammonites housed at the Silesian Museum in Opava. The material originates from historical collections in the Štramberk Limestone, mainly from the Kotouč Quarry (Baška Subunit of the Silesian Unit, Outer Western Carpathians). All favourably preserved specimens are undeformed external moulds. Six species are described; with the exception of Micracanthoceras microcanthum, all were previously unknown from the Štramberk Limestone. Kutekiceras steinbergense, Oloriziceras schneidi, and Franconites (Tithonosphinctes) stephanovi, together with M. microcanthum – a zonal index species of the lower upper Tithonian – are of Tithonian age. Hegaratia busnardoi and Kilianiceras ambiguum are assigned to the Berriasian (lowermost Cretaceous). Well-preserved ribbed specimens permitted the number of primary ribs per half-whorl to be counted at successive shell diameters. Rib counts are not constant during ontogeny: the phragmocone and the body chamber exhibit different rib densities. Furthermore, within the body chamber itself, the number of ribs changes with increasing shell diameter.