Two recognized species of the sauropod dinosaur Brachiosaurus have been described since the first, Brachiosaurus altithorax, was discovered in Utah in 1900. The other well-known species is that of Brachiosaurus brancai, discovered several years later in Tanzania. Two other species have been discovered in Portugal and Algeria, but the skeletal evidence is incomplete, and the species have not been fully identified yet—so far, they have only been identified as belonging to the genus Brachiosaurus.
Brachiosaurus is one of the largest known land animals, if not the largest. These dinosaurs measured about 23 m (75 ft.) long, and were about 12.6 m (41 ft.) high. Various weights have been estimated for Brachiosaurus over the years, some up to 80 t (88 tn.). A recent estimate based upon a 3D reconstruction of the B. brancai mount that is displayed at the Berlin Museum of Natural History suggests the body mass may have been in the order of 38 t (42 tn.).
Unusually, the front legs of Brachiosaurus are longer than the back legs, like those of modern giraffes. The name reflects this characteristic: it is based on the Greek words brachion for "arm" and sauros for "lizard". Elmer Riggs described and named Brachiosaurus in 1903, when he was working for the Field Museum of Natural History in Chicago.
Like all sauropods, Brachiosaurus was a herbivore. Fossil evidence suggests that these dinosaurs inhabited tropical riverbank environments, feeding on conifers, ginkgoes, ferns, horsetails and cycads.
Brachiosaurus lived approximately 150 million years ago, during the Late Jurassic Period. Later related forms lived into the Early Cretaceous Period.