Tyrannosaurus RexvsHippopotamus

This is a classic ancient-versus-modern heavyweight battle, and the size difference tells most of the story. A Tyrannosaurus Rex weighed approximately 15,000-20,000 pounds and stood 12-13 feet tall at the hip. A hippopotamus, while impressive at 3,000-4,000 pounds, is roughly a quarter of the T-Rex's mass. The physical mismatch is enormous.

The T-Rex's bite force is estimated at 12,800 PSI — the strongest of any terrestrial animal that ever lived. For comparison, the hippo's already-impressive 1,800 PSI bite force is barely a seventh of the T-Rex's. A single bite from the T-Rex could crush through the hippo's thick skin and bones simultaneously. The T-Rex was built to bite through the armored hides of ceratopsians and hadrosaurs, animals with far more natural protection than a hippo.

The hippo's only real advantage is its aggression and low center of gravity. Hippos are fearless and will charge anything that enters their territory, which is exactly the wrong strategy against a T-Rex. The hippo's 20-inch canines, while terrifying to crocodiles and lions, would barely scratch the T-Rex's thick, muscular hide.

Speed is surprisingly close — both animals could run at roughly 15-20 mph in short bursts. But the T-Rex's stride length and momentum at its size would be overwhelming. One charge from the T-Rex would flatten the hippo, and one bite would likely be fatal.