I can't see the bone very well in the pic but it might be a seal finger or toe bone. I tried to find a reference page for you on the seal but I didn't find anything helpful.

There are a couple of different types of the finger bones. One has a big knobby almost square end on it and the other is somewhat tapered and jointed on each end. I will post a couple of seal bones tomorrow if I get a chance. I actually know where they are for a change.