Copperjaw was a Tyrannosaurus rex living in the Rainy Basin in 1867. His age was unclear, but he was probably fully grown, since his size was used by Arthur Denison to compare the differences in body mass between a Tyrannosaurus and a Gigantosaurus. Copperjaw regularly attacked caravans in the Rainy Basin who got to close to the tyrannosaurid sacred ground that held the secrets of ancient Poseidos. He disliked allowing Arthur Denison, Oriana Nascava and Bix to enter the treasury, but was overruled by Sinktooth.