Dipnoan remains from the Lower-Middle Triassic of the Holy Cross Mountains and northeastern Poland, with remarks on dipnoan palaeobiogeography
Abstract Here we present a revision of dipnoans from the Middle-Upper Buntsandstein and the Lower Muschelkalk (Lower-Middle Triassic) of the Holy Cross Mountains (southeastern Poland) and from the Middle Buntsandstein of northeastern Poland. Two genera are identified: Arganodus and Ptychoceratodus. Specimens resemble synchronous species from the European part of Russia. It is the first Middle Triassic finding of Arganodus worldwide. Ptychoceratodus is reported for the first time from the Lower Triassic of Poland. It is its oldest known occurrence in Europe. The Holy Cross Mountains stands between the area of European Russia and the Central European Basin which were both inhabited by Arganodus and Ptychoceratodus in the Early-Middle Triassic. Resulting from a summary of palaeobiogeographic data of these two genera their distributional patterns are hypothesized herein. In the Early Triassic both genera often co-occurred in many regions. Starting from the Middle Triassic their ranges split into two almost separate ones. They reflect the palaeolatitudinal belts in the Late Triassic with Arganodus in the northern tropic belt and Ptychoceratodus along the palaeolatitudes 30°.