One of my favourite pieces, though apologies for the shitty photo - it was under arduous circumstances. But this is a horse's skull, seemingly used deliberately (or at least not discarded) from the backfilled roof of an opencut.
Also below that is a complete fox skeleton (as far as I could tell) found near the bottom of a very deep mine - though not at the bottom of the main shaft, but at the base of a complex system of climbing shafts and stopes, meaning the poor thing just kept wandering around in the dark, falling down more and more climbing shafts until it expired. This does mean though that it managed 120m of vertical workings, from surface, and all access routes were shafts. It's just about possible that it was actually a dog that belonged to a miner or mine owner, but apart from that it's a complete mystery. We also found a sheep's skull some way along a railed cartgate, 50m below surface, so god knows what they were doing down there - perhaps they ran a petting zoo when the price of lead was low?