Brachiosaurus is the biggest sauropod known from a complete skeleton. The biggest specimens show that it was one of the largest of all dinosaurs.

There were two species of Brachiosaurus , Brachiosaurus altihorax from western North America and Brachiosaurus brancai (sometimes called Giraffititan brancai ) from east Africa. The fact that it is found on both continents lends support to theory that the continents were joined by a land bridge during the Late Jurassic.

Brachiosaurus was unusual in that its front legs were longer than its hind. Very few animals have this adaptation. The long front legs of Brachiosaurus were used to improve its reach. The mounted skeleton of Brachiosaurus brancai in Berlin is over twelve metres tall.

Unlike some sauropods like Apatosaurus and Diplodocus, Brachiosaurus 's tail was quite small, and could not have been used in defence. The shear size of Brachiosaurus would have been enough to deter most predators.