Apatosaurus

The apatosaurus was a race of sauropod dinosaurs, surviving on prehistoric Earth. They are big, bulky, vegetarian and have incredibly long necks. They, like all other dinosaurs, were killed when the Cyber-Controller's ship crashed into the Earth. (DW: Earthshock) A few apatosaurs were briefly transported to the 1970s. (DW: Invasion of the Dinosaurs)

When fossils of the dinosaurs were found, some bones (including the head) were mixed up with other sauropod bones, so when discovered, the creatures were named Brontosaurus, after the combination of Latin words about its head. When the real head was found, Brontosaurus no longer made sense, seeing as the head was different, it was then renamed apatosaurus.