Apatosaurus

Apatosaurus, previously known as Brontosaurus, is a dinosaur that lived 150-145 million years ago during the late Jurassic period. It was a minor character in Fantasia appearing in "The Rite of Spring" segment despite it's fame.

Fantasia
It was first seen as a herd eating water grass. When the Tyrannosaurus lunged for the herbivores, Brontosaurus ran and watched its showdown with Stegosaurus. It is then seen marching with the other dinosaurs during the drought. They are then trapped in the muddy pit with other stegosaurs, and they die of heat exhaustion and are attacked by desperately hungry Ceratosauruses.

Trivia

 * Brontosaurus shares a lot of similarities with Diplodocus: they both are sauropods, both eat plants, both are diplodocoids, and both lived in the Jurassic Period.