Systematic Revision of the Oligocene Billfishes (Istiophoriformes: Palaeorhynchidae) from Romania

This study revises †Palaeorhynchidae (Istiophoriformes), a rare and taxonomically disputed group within Romania’s Oligocene ichthyofauna. Historically placed within Scombroidei, Istiophoriformes is now supported by molecular phylogenetics as a distinct lineage. However, prior Romanian fossil descriptions, often fragmentary, require critical revision to resolve their phylogeny, ecology, and biogeography. Outdated classifications must align with modern systematics. Our analysis confirms only two valid istiophoriform taxa in Romania’s Oligocene: †Homorhynchus colei, previously misassigned to †Palaeorhynchus longirostris or †P. glarisianus, and †Palaeorhynchus humorensis. This clarifies long-standing taxonomic uncertainties and underscores the need for integrative approaches in paleoichthyology. The findings refine regional Oligocene biodiversity records and highlight the Eastern Carpathians’ significance in understanding marine ecosystems of the epoch.