Brachiosaurus (pronounced /ˌbrækɪ.ɵˈsɔrəs/), meaning "arm lizard", from the Greek brachion/βραχιων meaning "arm" and sauros/σαυρος meaning "lizard", is a sauropod dinosaur that lived during the Late Jurassic Period and possibly the Early Cretaceous Period. It was named thus because its forelimbs were longer than its hind limbs. One of the largest animals known to have walked the earth, it has become one of the most famous of all dinosaurs and is recognized worldwide, but most frequently in the form of Giraffatitan, which was originally described as an African species of Brachiosaurus (B. brancai). Description Brachiosaurus was a sauropod dinosaur.  It had a giraffe-like build, with long forelimbs and a long neck. Brachiosaurus had "spatulate" teeth (resembling chisels), well-suited to its herbivorous diet. Its skull featured a number of holes, probably aiding weight-reduction. Skull The skull of Brachiosaurus was not identified until 1998, when Carpenter and Tidwell re-described a skull discovered by Othniel Charles Marsh in the 19th Century. Marsh had originally thought the skull belonged to Apatosaurus excelsus, but Carpenter and Tidwell found that it shared many similarities with African skulls belonging to the related Giraffatitan, and thus must have come from Brachiosaurus. The skull of Brachiosaurus is more camarasaur-like than the distinctive high-crested skull of Giraffatitan, which has traditionally been the basis of popular depictions of Brachiosaurus. Size Elmer S. Riggs’ assistant lying by a Brachiosaurus altithorax humerus during the excavation in 1900Many estimates of the size of Brachiosaurus from before 2009 are for the more complete material now assigned to Giraffatitan. However, a study comparing Brachiosaurus and Giraffatitan by Michael Taylor in 2009 found that the true Brachiosaurus specimens from North America actually represent heavier and likely longer individuals. Brachiosaurus is estimated to have weighed 28.7 tonnes (28.2 LT; 31.6 ST), compared to 23.3 tonnes (22.9 LT; 25.7 ST) for Giraffatitan. Additionally, the most complete and largest specimens of Brachiosaurus come from a sub-adult individual, so it likely would have grown larger than even current size estimates. Proportionally, Brachiosaurus had a longer torso and possibly a longer tail than Giraffatitan.