A revision of the pycnodont genus Phacodus and the description of a new species, Phacodus arghiusi sp. nov ., from the Eocene of the Transylvanian Basin, Romania

This study presents a taxonomic revision of the pycnodontiform fish genus Phacodus, based on new findings and re-evaluation of existing material.. Our results demonstrate that the name Phacodus punctatus and its junior synonyms are invalid; specimens previously assigned to this name should now be classified as Phacodus scrobiculatus nov. comb. Contrary to previous assumptions of a monospecific genus, we describe a new species, Phacodus arghiusii sp. nov., based on teeth recovered from three Eocene localities in Romania. The molariform teeth of P. arghiusii sp. nov. exhibit enameloid protuberances, the potential function of which in relation to trophic habits is discussed. The discovery of P. arghiusii sp. nov. underscores the need for further revision of Eocene fish fossils from the Transylvanian Basin and reveals a higher diversity for the genus Phacodus than previously recognized, with P. scrobiculatus now considered restricted to the Cretaceous and P. arghiusii to the Eocene of Europe. The temporal gap between these two species may be partially attributed to the scarcity of the global Paleocene pycnodont fossil record, especially in Europe and the Transylvanian Basin where marine deposits are poorly exposed, potentially suggesting a Lazarus taxon status for P. arghiusii sp. nov.