The comparative osteology and phylogenetic relationships of fossil and living paddlefishes (Polyodontidae) are investigated in detail for the first time. This peculiar, poorly known group is of great significance to phylogenetic studies of primitive actinopterygians, because it is one of only two chondrostean families that have survived to the present. Consequently the group is frequently used as an outgroup for studies of the many fossil chondrostean groups and for higher-level studies of actinopterygian (and even osteichthyan) interrelationships.