Brachiosaurus dinosaur, artwork. Brachiosaurus was the tallest dinosaur, standing up to 16 meters tall. Unusually for a dinosaur, its front legs were longer than its hind legs. It is thought that it fed on the high leaves of trees, as giraffes do today. Fossils of Brachiosaurus have been found in North America and Africa. It lived in the late Jurassic period, between 155 and 145 million years ago. It is thought that Brachiosaurus lived in herds, although a fully- grown adult would have had little to fear from predators.