Dinosaurs that never really existed

Quick explanation:
Paleontologists like to be react upon discovering a fossil by naming what seem to be new discoveries that later turn out to be the same as a previous discovery, as in the case of Brontosaurus/Apatosaurus
Additionally, because of the way new discoveries are (or at least WERE) explained to the public and shown by journalists, scientific language got misused and then stuck. Calling all Pterosaurs Pteradactyls is equivalent to calling all birds chickadee (also, sidenote: calling Pterosaurs dinosaurs is like calling birds dogs).
The third case of the Triceratops, I must note, is true but not exactly. It has recently been discovered that the Triceratops is the juvinile of the larger Torosaurus, but what is likely to happen is that the Torosaurus will become considered an adult Triceratops and not the other way around.

So yah! fun stuff all around! yay science!