Revision of haploceratid ammonoids from the Štramberk Limestone, Jurassic–Cretaceous boundary beds (Outer Western Carpathians)

Haploceratids from the Štramberk Limestones represent three genera Haploceras, Hypolissoceras, and Volanites. The most species reach genus is Haploceras. The semi-involute shells of the local haploceratids are almost smooth or only with a specific sculpture bound to the ventral region near the peristome. The whorls tend to be weakly arched or flat. Statistical elaboration of H/D, U/D and B/D values during shell growth shows no significant differences between these values, except perhaps for U/D. The external morphology plays a decisive role in the generic and species identification of haploceratids. It is known that haploceratids form dimorphic pairs, as evidenced by the differently shaped peristomes in addition to the different shell sizes. Dimorphic pairs have been demonstrated as new in the Štramberk material for the pairs Haploceras staszycii (microconch, m) and Haploceras elimatum (macroconch, M), as well as Hypolissoceras carachtheis (m) and Hypolissoceras woehleri (M). Haploceras tithonium and Volanites verrucosus possessed dimorphic pairs but their counterparts have not been found in the Štramberk Limestone. With the exception of Volanites verruciferus, the species described here are of no stratigraphical importance. Their stratigraphic range is from the lower Tithonian to the lower Berriasian.