Now see the story of Hercules killing Nemean lion. Once there was a fierce lion roaming ancient Nemea in Greece. Eurystheus ordered Hercules to kill the Nemean Lion. Accordingly Hercules went and killed the lion. After killing the Nemean, Hercules skinned the lion and wore the skin like a coat of Armour.
Now, what is the similarity of this story with the story of Krishna. this story is now part of 10 avatars of Vishnu. Read the story of Narasimha killing demon Hiranya Kashibu.
The pictures of Hercules shows that he wears the Lion Head as a hood to his head (Hercules wore the lion head like a helmet). Which is similar to the picture of Narasimha here. the conclusion is that the original story is that off Hercules, and that story got modified into Narasimha story of india. The implication of this idea is that the origin of Baghavatham should be fixed only after Alexander's invasion (i.e.300BC), and the idea is originally a Greek idea borrowed by Indians (or) the other way of telling will be that," This idea was imposed on Indians by invading Greeks". Not much earlier period as being claimed by many Indians.
Narasimha Avatar(Picture from Wikipedia).