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 tarphyceratid 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 Dobrotivá 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 regarding 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 Zahořany 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. [ABSTRACT FROM AUTHOR]