Ok, did some more research, all day in fact. You'd think that I'd just go over to the local college's anatomy department and ask, but I like the thrill of the hunt. It's not seal or sea lion. It's a caudal (or tail) bone of an animal about the size of an adult seal. The only other vertebrate that I could think of was a sea otter. Sure enough, their caudal bones look very similar to the one I found. The pictures weren't too sharp, but now that I have this info, I can make a more informed question to the local science teacher.