In 1988 , Gregory S. Paul said that there were some differences between the Brachiosaurus brancai and the North American Brachiosaurus , so he created a subgenus called Brachiosaurus ( Giraffatitan ) brancai . In 1988 , Gregory S. Paul noted that Brachiosaurus brancai ( on which most popular depictions of Brachiosaurus were based ) showed significant differences from the North American Brachiosaurus , especially in the proportions of its trunk vertebrae and in its more gracile build . Paul used these differences to create a subgenus he named Brachiosaurus ( Giraffatitan ) brancai .