Apatosaurus

The Apatosaurus is the biggest dinosaur found in the valley of Eodon, being up to 120 feet long.

Description
This animal is actually no threat at all, apart from the fact that it could accidently step on a careless adventurer. They are vegetarians and mostly spend their time either in water or standing in the swamp, where predators like the Allosaurus don't dare to enter.