Dreadnoughtus

Wild

Dreadnoughtus was a newly-described fossil genus in my day, named for the idea that it was so large it must've had nothing to fear in its own time. The current species does its namesake proud, and may even be able to defy the Titans ruling our post-apocalyptic world. A big believer in picking on creatures its own size, Dreadnoughtus will ignore anything smaller than a Spinosaur to focus on larger threats. It absorbs the fury of incoming attacks to charge up its uncanny, Element-disrupting bellow. Even then, this bruiser shows extraordinary patience, waiting until the last possible moment to come roaring back.

Domesticated

Once tamed, Dreadnoughtus will gladly shoulder your heaviest artillery and carry it -- and you -- into battle, on a platform big enough to earn that 'dreadnought' name. Your walking war-machine will swallow boulders (or cannonballs!) to spit back up as acid-coated ammo. If you're going to war with Titans, it just makes sense to recruit a titanic creature with a grudge against them. Your Dreadnoughtus ally may go down fighting, but not before softening up the adversary for a killing blow. Best of luck, and give 'em Hell for me!