Fossils collected in Osaka more than 30 years ago have revealed a surprise hiding in plain sight: four previously unrecognized bones from a giant Cretaceous mosasaur. Among them is the first confirmed premaxilla—the frontmost bone of the upper jaw—ever identified in a Japanese mosasaur fossil. Even more intriguing, parts of the skull show unusual anatomical features that don’t match known mosasaurs, raising the possibility that the remains belong to an entirely new species.