MegalodonvsTyrannosaurus Rex

This fight depends entirely on environment, and the only viable environment is shallow coastal water — the T-Rex can't swim and the Megalodon can't walk.

In water, the Megalodon dominates absolutely. At 50+ tons versus the T-Rex's 9 tons, with a bite force of 40,000+ pounds (vs the Rex's 12,800), the Megalodon would devour the T-Rex like a snack. In the water, the T-Rex loses all mobility and becomes prey.

On land, the Megalodon is a beached fish and the T-Rex wins by default. In shallow water where both can operate, the Megalodon's aquatic superiority gives it the decisive advantage.