I have been reading my copy that I have of The Tyrannosaur Chronicles, and in the chapter about prey, there was a picture that was captioned Hell Creek Prey. There were Edmontosaurus, Triceratops, Thescelosaurus, but there was also a sauropod. I looked through @Troodons topics about the hell creek fm and also the wikepedia page about hell creek fauna. Is the book outdated or is there actually a sauropod dinosaur in the Hell Creek Formation?