Bone

Every so often, knowing that I once studied geology, someone will bring me a rock or a fossil to identify. This has led to some wonderful conversations - is it a meteor? No, a piece of metamorphic. Is this a fossil, sadly no, but a nice piece of glass. Today, a colleague brought me a wonderful fossilised bone to identify. It is certainly a fossil bone from sediments about 350-450 million years ago, but I do not have the expertise to identify the species. I this it was a large mammal, but my speculation ends there. (With a 5p for scale). On top of the bone there was also small ammonite, but that might just confuse the issue!
as also a