Plateosaurus is one of the earliest, large dinosaurs. These creatures had a maximum size of roughly 25 feet long and 1.5 tons. Plateosaurus was probably able to rear up on it's back legs to reach food that was high off the ground. These prosauropods were a sign of things to come in the Jurassic when the giant sauropods would appear. Plateosaurus lived 220 million years ago in Europe.