I am, however, buggered if I know why.
In fact, similar to ducks’ legs. Two of them were both the same.
Some bloke found a little one, called it (now i know it was) Apatosaurus, then he or maybe someone else, found a much bigger one and thought it was a different animal so called it Brontosaurus. Then they realise that they already had one of those, so they could get rid of it