I don't know much (ie anything) about skeletal remains, but what you have marked as a nail like protuberance is actually a front tooth. Based on the size of what is a fragment of the jaw from an animal, I'd guess (badly probably) that it is from a rodent of some description, or a young farm animal.
Hopefully one of the expert posters will be along to help with the ID.
This is a piece of a rabbit jaw. Like Jonathan said, that nail is actually one of it's incisors.
Thanks for the feedback. This must be a very small fragment though because it is only around 4cm long??
Rabbit mandibles don't get much bigger than that! I've measured the pieces I have and they average out to about 6-7cm long (not broken).