Brachiosaurus is a genus of sauropod dinosaur that lived in North America during the Late Jurassic, about 154 to 150 million years ago. It was first described by American paleontologist Elmer S. Riggs in 1903 from fossils found in the Colorado River valley in western Colorado, United States. Riggs named the dinosaur Brachiosaurus altithorax; the generic name is Greek for "arm lizard", in reference to its proportionately long arms, and the specific name means "deep chest". Brachiosaurus is estimated to have been between 18 and 22 meters long; body mass estimates of the subadult holotype specimen range from 28.3 to 46.9 metric tons. It had a disproportionately long neck, small skull, and large overall size, all of which are typical for sauropods. Atypically, Brachiosaurus had longer forelimbs than hindlimbs, which resulted in a steeply inclined trunk, and a proportionally shorter tail.
Brachiosaurus
Elmer S. Riggs's preparator, H. W. Menke, lying by the humerus during the excavation in 1900
Riggs (right) and J. B. Abbott working on the holotype bones in 1899. The still-jacketed thighbone can be seen on the left.
O. C. Marsh's outdated 1891 skeletal reconstruction of Brontosaurus, with skull inaccurately based on that of the Felch Quarry Brachiosaurus
Sauropoda, whose members are known as sauropods, is a clade of saurischian ('lizard-hipped') dinosaurs. Sauropods had very long necks, long tails, small heads, and four thick, pillar-like legs. They are notable for the enormous sizes attained by some species, and the group includes the largest animals to have ever lived on land. Well-known genera include Apatosaurus, Argentinosaurus,
Alamosaurus, Brachiosaurus, Camarasaurus, Diplodocus, and Mamenchisaurus.
Sauropoda
Reconstruction of Ampelosaurus
Some sauropods, such as Alamosaurus sanjuanensis, formed herds segregated by age.
Cast of Toni, a juvenile brachiosaurus (restored as a diplodocid)