This is a monster (dragon?) from a marble statue called the discus bearer. The statue was originally produced in bronze by Polykleitos (460-450 bc) and we can be quite sure that the dragon was added when the statue were copied - it is a part of the support that is required in the marble version.
"Æthiopia produces dragons [lat. draconi], not so large as those of India, but still, twenty cubits in length.1[sic] The only thing that surprises me is, how Juba came to believe that they have crests"
Pliny the Elder - Naturalis Historia (the Natural History) VIII.13
Translated by John Bostock, H.T. Riley