T. Rex was initially going to be called Stegosaurus - until they realised there was a death metal band in Finland with the same name
Funny detail: this Finnish band changed their name to Tyrannosaurus R.
Stegosaurus was really a place holder name. It seemed better than "unnamed project of Stego Larrssen and Gustav Saurus". It was an odd project not because Stego insisted that his last name be pronounced Larrrrr-sssssen, but because Larrssen is a vocalist/drummer and Saurus is a singer/percussionist. Eventually, they fired each other.