Interesting relic, I've spent a lot of time around old railroads and I can't remember seeing anything like it. I don't think it's a spike puller though, for a couple reasons. First all of them I have seen are made completely of steel and look more like a giant crowbar. I can't imagine they'd have one with a wooden handle. The other thing is, it looks like it's cast iron, rather than steel, and I think it would be too brittle for that kind of use.
You might want to send pics to a railroad museum and see if anyone can help. The problem is that things along the tracks could literally come from almost anywhere. It could have fallen out of a gondola full of scrap iron, hard to say.