The nomenclatural history of Giraffatitan is intricately tied to Brachiosaurus, as it has been referred to that genus for over 70 years.

The original or, type, species of Brachiosaurus is B.altithorax (high-chested arm lizard), named by Elmer Riggs in 1903. This species is based on a partial skeleton found in the western U.S. In 1914, Werner Janensch described the remains of similar remains collected in Tanzania. Janensch assigned these remains to Brachiosaurus, but he considered them distinct enough from B. altithorax to erect a new, African species: B. brancai. Enough B. brancai material was collected for the Humbolt Museum fur Naturkunde in Berlin to mount a skeleton composed of the bones of several individuals, and this has provided the basis for almost every illustration of Brachiosaurus ever published.

In 1988, Gregory Paul noted that the few elements of B. brancai that were directly comparable to B. altithorax showed that these two species were more distantly related than Janensch had thought. Paul proposed that they be divided at the level of subgenus, a rank in between species and genus. Three years later, George Olshevsky took it one step further, and elevated Giraffatitan to generic status, separating G. brancai from Brachiosaurus.

The use of Giraffatitan (as either genus or subgenus) has not been widely accepted. Ultimately it boils down to how distinctive specimens must be to be separated at any given level. Are these two different species of Brachiosaurus, subgenera of Brachiosaurus, or genera of brachiosaurids? Questions like these are usually answered by individual philosophies of taxonomy, and reflect the subjective side of biological classification. The promotion of Giraffatitan here is not the result of extensive research or comparison, but simply because it enables this story to be more easily told, and it is just too goofy a name for us to pass up.