Brachiosaurus was one of the largest animals that has ever lived on this planet. It was a saurischian (lizard hipped) sauropod type dinosaur that lived over 150 million years ago during the last half of the Jurassic period. It was a quadruped, meaning that it walked on all fours, though on occasions it may have reared up on its hind legs to reach the topmost branches of the trees. Unusually for a dinosaur, its front legs were longer than its hind legs.

Having such a large bulky body would have meant it had few predators; Allosaurus would probably have preyed on young and sick animals but an adult would present an almost impossible challenge, even for those skilled killers.

The great size of Brachiosaurus was not without its own challenges; to get blood to the head needed a large powerful heart, as big as a modern small car, that pumped the blood at a very high pressure up the long neck to the brain. This requires big, muscular blood vessels packed with valves to prevent the blood flowing back. An unusual feature of Brachiosaurus was its nostrils; they were placed at the top of its head. The reason for this was originally thought to be because they were aquatic animals living in water to support their great weight, but this theory has since been disproved; a deep narrow body and relatively small foot print are not features suitable for living in water.

Brachiosaurus' are thought to have lived in herds that browsed amongst the tree tops, moving on after they had exhausted the local food supply. To do this they had 52 chisel shaped teeth, 26 in each jaw, at the front of the mouth for stripping the foliage from the branches. They may also have swallowed stones to help grind up the rough vegetation in the stomach.

The life span of these animals is thought to have been up to 100 years; early life would have been hazardous, however, as Brachiosaurus did not look after its young, and infant mortality rates would have been high.

Brachiosaurus fossils have been found in North America and  Tanzania in Africa. During the age when Brachiosaurus lived these two places were connected as part of a large super-continent and the range of Brachiosaurus was huge possibly even into modern day Europe. The first fossils were found in the Grand River Valley in Colorado, North America, in 1900. Palaeontologist Elmer Riggs later examined these finds and named the animal Brachiosaurus in 1903.