Sorry for the delay. First, let's meet our contestants:
Tyrannosaurus was a large carnivore that lived in the United States and Canada in the Late Cretaceous.
Diplodocus was a large herbivore that lived in the United States in the Late Jurassic
A lone male Diplodocus is walking through a field near a forest. It doesn't realize one thing: it's being stalked by one of nature's greatest predators. The Diplodocus continues to try to find something to eat. After a couple of minutes, the predator runs at the Diplodocus. The predator is a Tyrannosaurus! The Diplodocus acts fast and whips the Tyrannosaurus in the leg with it's long tail.
The Tyrannosaurus roars in pain, but continues to try to attack. She lands a couple of blows in the Diplodocus' hide, but it's too thick to do any serious damage. After a few minutes, the confrontation is over and the Tyrannosaurus walks away. It's not defeated; it's planning something!
The Tyrannosaurus crouches in some bushes, waiting for the moment to strike. She watches the Diplodocus wander off, and now the perfect moment comes! The Diplodocus is happily swallowing some ferns, and doesn't notice the Tyrannosaurus running at it. The Diplodocus notices just in time, and swings it's long tail. The Tyrannosaurus bites off about one-third of it, taking away the Diplodocus' main weapon. However, the tail wasn't the Diplodocus' only attack.
The Diplodocus swings it's long, thick neck, much like a modern day giraffe. However, this fails when the Tyrannosaurus dodges the first atempt and bites the Diplodocus behind the head. Now, the Diplodocus is weaker, and rears up on it's hind legs, looking down at the Tyrannosaurus. He crashes back down, attempting to crush the Tyrannosaurus with his front feet. Now, the Tyrannosaurus is gone. The Diplodocus dosen't see it, and continues eating.
The Tyrannosaurus makes one final attack, biting the Diplodocus in the head. The Diplodocus struggles to get free, but the Tyrannosaurus pushes it down with her arms, left leg, and mouth. She finishes off the sauropod and eats. She must hurry, because soon crowds of carnivores will try to steal this kill, including the largest two on the island.
It's intelligence, power, and mouth made up for size in this battle.