A new Triodus shark species (Xenacanthidae, Xenacanthiformes) from the lowermost Permian of France and its paleobiogeographic implications

The Xenacanthiformes from Central and Eastern European deposits have been extensively studied, but the systematics of the species from the French Carboniferous-Permian Autun Basin (Saone-et-Loire) remains debated. Numerous xenacanthiform remains are still identified under the doubtful genus `Expleuracanthus', and many of them consist of isolated dorsal spines which are difficult to identify. Numerous well-preserved specimens are still undescribed and the diversity of the xenacanthiform fauna from the Autun Basin is poorly understood. For example, specimens of the genus Triodus from the Muse oil-shale bed (OSB) of the Autun Basin have no specific attribution, whereas this genus is widely distributed across European Carboniferous-Permian basins. In this study, we describe new specimens of Triodus from the lowermost Permian of the Muse OSB. They allow the erection of a new species, Triodus aeduorum sp. nov., and discussion of the validity of several species from the same locality: `Expleuracanthus' frossardi is considered as a nomen dubium and other Triodus specimens need for the time being to be left in open nomenclature as Triodus sp. These results highlight the endemism of the Triodus species in each European Carboniferous-Permian basin and raise the question of how they migrated from one to another.