The tarphyceratid cephalopod Trocholites in the Middle-Upper Ordovician of the Prague Basin -the Baltican element in peri-Gondwana

The vast majority of cephalopods of the order Tarphyceratida are known from regions that were located at mid-or low palaeolatitudes during the Ordovician (mainly Baltica, Laurentia, and Chinese palaeoblocks). Only a handful of tarphy-ceratid specimens are known from high palaeolatitude regions of peri-Gondwana and Gondwana. Here, we describe the two best-preserved trocholitid cephalopods known to date from the Ordovician of the Prague Basin. The first is from the late Darriwilian/early Sandbian Dobrotiva Formation and is assigned to Trocholites fugax, a species previously recorded from roughly coeval strata of Iberia, France, and Bohemia. The specimen thus strengthens previous hypotheses regard-ing the interchange of non-benthic faunas between Baltica and different regions of peri-Gondwana during the Middle/ Late Ordovician boundary interval. The second specimen, assigned to a new species of Trocholites chaloupkai sp. nov., is from the late Sandbian-early Katian Zahorany Formation and thus represents one of the stratigraphically youngest Trocholites in the Ordovician of peri-Gondwana. Internal structures of the shell of the holotype of the new species were studied using micro-CT tomography. This revealed that T. chaloupkai sp. nov. closely resembles the stratigraphically older (Darriwilian) species Trocholites depressus from Estonia.

Automated summary

This study describes two well-preserved cephalopod species of the order Tarphyceratida from the Ordovician of the Prague Basin. One species, Trocholites fugax, has been found in coeval strata of Iberia, France, and Bohemia, supporting the hypothesis of interchange of faunas between different regions during the Middle/Late Ordovician boundary. The other species, Trocholites chaloupkai sp. nov., is one of the stratigraphically youngest Trocholites known in peri-Gondwana.