treasure!

Just watching "The Goonies" right now. Actually, what is the rule on buried treasure and the like? I mean, let's say you do find the horde of some famous pirate? Can you keep it for yourself? Or would some archeologist say you couldn't? Or, if someone could prove they were the descendant of someone who was robbed by the pirate, would they be able to claim some of the treasure? It just seems nowadays there are rules preventing you from just taking something from the ruins of an ancient civilization for yourself, and I would think that would fall into the same category. I could be totally wrong though.