 Though experts believe stegos use their tail spikes to fight, this one shows no sign of combat. It does show signs of arthritis, however, so it suggests Apex lived a long and pretty healthy life. Sotheby's estimates it'll sell for something like $4 or $6 million, but this is the first time a stegosaurus of this size and caliber will go up for auction, so it could go for a whole lot more.