Just think of Brachiosaurus as the giraffe of the Jurassic period. With its 30-foot-long (9 m) neck, Brachiosaurus could easily browse for breakfast in the highest treetops. In fact, it was the tallest dinosaur of its time, reaching four stories in height.
An adult Brachiosaurus probably had no natural enemies, but babies needed protection. Fossilized footprints show that at least some long-necked "sauropods" like Brachiosaurus traveled in herds, with adults on the outside of the group and juveniles in the middle for safekeeping.
On July 4th, 1900, a colleague of famous Field Museum paleontologist Elmer Riggs found what was thought to be a Brontosaurus femur (thigh bone). But while preparing the fossil, Riggs realized it was actually a humerus (upper arm bone)—and far too large to belong to a Brontosaurus (which he later recognized should be called Apatosaurus).
Riggs realized he'd discovered an entirely new kind of dinosaur, and christened it Brachiosaurus ("arm lizard"). You can stand beneath a cast of this towering giant outside The Field Museum and view the real 6.5-foot-long humerus in the Evolving Planet exhibition.