Brachiosaurus was a species of sauropod. Sauropods were big-bodied, four-legged herbivores with long necks and tails. Huge sauropods, like Brachiosaurus, were able to support their immense body size thanks to air sacs in their bones and body cavity, making them relatively lighter and stronger.

Brachiosaurus stood taller than most other herbivorous dinosaurs, allowing it to browse from the tops of trees. It did not have teeth capable of chewing, so it swallowed foliage whole.