Skeletal morphology and phylogenetic relationships of the Late Cretaceous freshwater ray Myledaphus bipartitus (Chondrichthyes; Batomorphii).

In this study, we present the first comprehensive description of the skeletal morphology of the freshwater-tolerant ray †Myledaphus bipartitus, a Late Cretaceous batomorph known from North America. These new data are based on an exceptionally well-preserved specimen from the Campanian of the Dinosaur Park Formation in Alberta, Canada, which provides valuable morphological details previously lacking for this taxon. A detailed morphological analysis was conducted, which revealed a unique combination of plesiomorphic and derived characters. Phylogenetic analyses provide support for the placement of †M. bipartitus within the order Rhinopristiformes, a group that includes modern guitarfishes and sawfishes. As the oldest known freshwater-tolerant representative of Rhinopristiformes, †M. bipartitus thus offers novel insights into the early ecological diversification of this group. The present study underscores the broader necessity for comprehensive morphological and systematic research on Late Cretaceous batomorphs. Nevertheless, the obtained results demonstrate the value of combining detailed morphological data with rigorous phylogenetic methods to elucidate the evolutionary history of extinct and extant batomorph lineages.