Interesting, but I doubt the bit about the thumb indentation in the wood.  It is on the shorter end for an unbacked bow, so I wonder if it is Osage.  I also wonder if it was meant to be shot from a canoe, and that is why it is so short?  I also wonder what the draw weight length was.  Finally, do you think the bow was buried there by the original owner?  I have heard of people doing that for various reasons.