30-year-old fossil hid bones of a mysterious ancient sea monster

Fossils collected in Osaka over 30 years ago contained four previously unrecognized bones from a giant Cretaceous mosasaur. Among them is the first confirmed premaxilla — the frontmost upper jaw bone — ever found in a Japanese mosasaur fossil. Unusual skull anatomy that doesn't match any known mosasaur raises the possibility these remains belong to an entirely new species.