BRACHIOSAUR

any member of a genus (Brachiosaurus) of sauropod dinosaurs that lived during the Late Jurassic Epoch (163 to 144 million years ago) in Africa, North America, and Europe. They were the heaviest and largest sauropod dinosaurs for which a complete skeleton exists; larger fossil bones belonging to other and possibly related sauropods have been found but are incomplete. Brachiosaurs were built like huge giraffes; they had immensely long necks and, unusual among the dinosaurs, forelimbs that were considerably longer than their hind limbs. These adaptations apparently enabled them to lift their heads to great heights in order to browse on the leafy branches of tall trees. Brachiosaurs attained a length of at least 23 m (75 feet), a head height of 12 m, and a weight of 80 metric tons. They had a deep, domed head that terminated in a broad, flat snout. The huge size of brachiosaurs led some researchers to theorize that they spent most of their time submerged in water, which would have served to buoy up their great weight. The location of the nasal openings on top of the head, and above the eyes, lent additional support to this theory. But water pressure at depths needed to cover these dinosaurs would have crushed their lungs, making breathing difficult or impossible. It is now generally thought that brachiosaurs were well adapted to a life on land, browsing on high treetops. Owing to a strong but relatively lightweight bone structure, their legs and skeletons were probably robust enough to support their full weight without any help from water.