Understanding the Westphalo-Stephanian ichthyofaunal turnover with the contribution of the Vaulnaveys-le-Bas locality (Isère, France)

The fossil record of Pennsylvanian actinopterygians from Europe is particularly rich, notably thanks to the Westphalian paralic sites of Northwest Europe, and the late Westphalian–Stephanian Variscan Intra-mountainous basins (VIB). So far only eight formations documented the temporal overlap of these two provinces (Bruay, Pas-de-Calais-Charleroi; Kladno, Kumburk, and Odolov, Bohemian Massif; Gagnières and Rive-de-Gier, French Massif Central; Dilsburg and Göttelborn, Rhenish Massif), with scarce remains in seven of them. Here we describe a Westphalian D (= late Moscovian) ichthyofauna from the Vaulnaveys-le-Bas locality, in the La Mure Basin sensu lato (Isère, France). This ichthyofauna consists of isolated scales and bones representing actinopterygians (Aeduellidae indet. and Actinopterygii indet.) and the tetrapodomorph cf. Rhizodopsis sp. These discoveries are the first known fossil vertebrates from the Westphalian D of a VIB in France. They fill a gap in the fossil record of these basins, with the oldest occurrence of Aeduellidae and only the second occurrence of Rhizodopsis in the VIB. The Vaulnaveys-le-Bas ichthyofauna documents a faunal transition occurring at the end of the Westphalian in the VIB: the Westphalo-Stephanian ichthyofaunal turnover. Faunas previously typical of the paralic province in Northwest Europe (i.e., Rhizodopsis) make incursions into the VIB, where new endemic groups emerge (i.e., Aeduellids). These endemic groups are unknown in older deposits and have no close relatives in the paralic province. Paralic taxa are then absent in the younger basins of Stephanian B, where they are completely replaced by these endemic groups.