This note proposes a new interpretation of a scene on a well-known Corinthian vase illustrating the Homeric legend of Herakles rescuing Hesione from the Monster of Troy. Commentators have assumed that the artist intended to depict the monster as a ketos, an imaginary sea monster, but the features of the beast do not conform to the traditional imagery of sea monsters in Greek art. I suggest that instead of creating a typical hybrid sea monster by mixing the features of various living creatures, this artist used for his model the large fossil skull of a prehistoric mammal. The vase was painted in the midst of widespread interest in large fossil remains, which the ancient Greeks identified as relics of giants and monsters of the mythological age. The features of the odd head on the vase match the basic skull anatomy of a large mammal of the Tertiary age, such as the Samotherium, a giant giraffe of the Miocene epoch. Numerous literary accounts describe exposures of these and similar large mammal fossils in antiquity along the Turkish coast, on Aegean islands, and on the Greek mainland. I conclude that this vase painting is the earliest artistic record of such a discovery.