Revision of some stratigraphically relevant ammonoids from the Cassian Formation (latest Ladinian-Early Carnian, Triassic) of St. Cassian (Dolomites, Italy)

Ammonoid species of the genera Arpadites, Klipsteinia, Muensterites, Protrachyceras, and Sirenotrachyceras from the Cassian Formation/Formazione di San Cassiano of the St. Cassian area/Dolomites (latest Ladinian-Early Carnian, Triassic, Italy) are revised. Lectotypes are designated for Arpadites busiris, Protrachyceras ladinum, Sirenotrachyceras hadwigae, and Sirenotrachyceras rudolphi. Protrachyceras aequinodosum (KLIPSTEIN) is an older synonym of the late Ladinian Protrachyceras ladinum. In the canadensis Zone of the GSSP Stuoreswiesen/Prati di Stuores, Sirenotrachyceras is absent and the occurrence of Trachyceras is strongly questioned. Klipsteinia, Sirenotrachyceras, and Badiotites are typical ammonoid genera from the aon and aonoides zones of the St. Cassian area. They are missing in the subsequent austriacum Zone of the Dolomites and therefore, the extinction event at the base of this zone is also evident from the ammonoid record. In marlstones of the Cassian Formation mainly juvenile to subadult ammonoids occur; adults are rare. In claystones, mainly early juvenile ammonoids with normal-spaced sutures are present, which deceased premature due to unfavourable life conditions. The only exception is Lobites, where adults predominate both in marl- and claystones. The specimens from marlstones are normal-sized, whereas those from claystones are stunted.