What makes a trophy "mountable"?

[Goldtip]

Some of the animals I have mounted are more about who I was with than their size, my shoulder mount bull elk is not the biggest I've killed, but the only elk I've killed with my brother by my side. The antelope had the prettiest cape on any antelope I've killed and my dad was sitting right next to me when I killed it. My quebec caribou, well it was the biggest of the two I killed. My whitetail, well it is my biggest whitetail. Some of the others are just the prettiest I've killed or the biggest, but the something special about that particular hunt is usually what get's the animal a trip to the Taxi for me.