Brachiosaurus was one of the biggest land animals ever. Its weight has been estimated at about 80 tonnes, twenty times heavier than a large elephant. It takes its name from the prodigious length of its front legs. Unlike other dinosaurs it's front legs were longer than it's hind ones, so that its back sloped upwards towards the head. In the Natural History Museum in Berlin there is a mounted Brachiosaurus skeleton; its head is 13 metres above the ground and its upper arm bone is over 2 metres long. It dwarfs the Diplodocus standing next to it.

With close cropping teeth for nipping food, Brachiosaurus was adapted to eat the most elevated plant material such as conifer leaves and fruit. Its upright stance and elevated neck meant that it could graze from trees at heights no other sauropod could reach. With comparatively short jaws, and chisel-like teeth it could nip leaves and fruit from tall conifer trees. It had unusually large nostrils on the top of the skull which may indicate that it had a powerful sense of smell.

It was first described by Elmer Riggs on the basis of an incomplete skeleton discovered in 1900 at the Grand Junction, Colorado, USA. A few years later several very fine skeletons were found at Tendaguru in Tanzania.