Apatosaurs

Apatosaurus skeleton (regrettably with a droopy tail) against the backdrop of the Yale Peabody Museum's famous dinosaur mural.

More commonly known as Brontosaurus, Apatosaurus reverted to its original scientific name after paleontologists discovered that O. C. Marsh—in his haste to name more species than his nemesis E. D. Cope—had accidentally named the same species twice.