Middle Triassic Nautilida from the Besano Formation of Monte San Giorgio, Switzerland

For the first time, nautilids from the Besano Formation (Anisian/Ladinian boundary) are documented. The extremely rare material was collected from two different outcrops at Monte San Giorgio (Southern Alps, Ticino, Switzerland). This material is represented by only five specimens described here. The three best specimens belong to the taxa Enoploceras rieberi sp. nov., Germanonautilus aff. ellipticus and Syringonautilus sp. indet., documenting the presence of the families Tainoceratidae and Syringonautilidae in the middle Besano Formation. Another nautilid specimen is described in open nomenclature, representing an additional taxon. The new species Enoploceras rieberi n. sp. is currently the only occurrence of the genus Enoploceras in the Middle Triassic. Nautilida are poorly known from the Middle Triassic Tethyan region, mostly from sediments deposited in pelagic environments. This is the first record of these nautilids from an usually anoxic depositional paleoenvironment of an intra-platform basin, where the sediments of the Besano Formation were laid down.

Automated summary

For the first time, the presence of nautilids from the Besano Formation has been documented. Five specimens were collected from Monte San Giorgio in Switzerland, representing three different taxa. The study reveals the occurrence of Tainoceratidae and Syringonautilidae families in the middle Besano Formation. Additionally, one nautilid specimen representing another yet unnamed taxon was described. The discovery of the new species Enoploceras rieberi marks the first occurrence of the genus in the Middle Triassic. This finding is significant as nautilids from the Middle Triassic Tethyan region are poorly known, and this is the first record of them in anoxic depositional paleoenvironments of an intra-platform basin.