First report of fossil Masturus (sharptail mola) from the Miocene Hagjeon Formation, southeastern Korea

We report the first fossil occurrence of Masturus from the Middle Miocene Hagjeon Formation of the Pohang Basin, southeastern Korea. It is referable to Masturus cf. lanceolatus based on a distinctive combination of features, including a fused upper beak formed by premaxilla, eight caudal vertebrae, a clavus bearing posteriorly positioned middle fin rays, a clavus margin with a median projection, absence of ossicles on paraxial clavus fin rays, and a dome-shaped epioccipital that is only moderately prolonged posterodorsally. The specimen is a nearly complete skeleton preserved in lateral view within dark gray mudstone and retains soft tissue impressions interpreted as dermal scale imprints. The dorsal and anal fin ray counts (20 and 17) fall within the range of extant Masturus lanceolatus. The fossil is extremely small, with a total length of about 9 cm, and the inferred posterior prolongation of the middle fin is most consistent with a juvenile individual, potentially corresponding to an early ontogenetic stage in extant Masturus. Because juvenile comparative skeletal data are limited and the temporal separation from the extant species is substantial, a confident species-level assignment is not possible. This discovery demonstrates that the molecular phylogenetic analysis (7.2–18.9 Ma) is corroborated by the paleontological record, provides the first calibration point for Masturus evolution, and enriches our understanding of Miocene pelagic ecosystems on the Korean Peninsula.