Brachiosaurus was a sauropod, one of a group of four-legged, plant-eating dinosaurs with long necks and tails and relatively small brains. Unlike other families of sauropods, it had a giraffe-like build, with long forelimbs and a very 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. The first toe on its front foot and the first three toes on its hind feet were clawed. 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 the 1998 study 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.

 

For many decades, Brachiosaurus was among the largest dinosaur known, especially when complete specimens (now classified as Giraffatitan) were attributed to it. However, a study comparing Brachiosaurus and Giraffatitan by Michael Taylor in 2009 found that the true Brachiosaurus specimens from North America actually represent a heavier, likely longer individual. In fact, 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.

 

The first Brachiosaurus specimen was discovered in 1900 by Elmer Riggs, (pictured left) in the Grand River Canyon of western Colorado, in the United States. He first published on his findings and named the species Brachiosaurus altithorax in 1903, declaring it "the largest known dinosaur." Brachiosaurus altithorax is known from two partial skeletons recovered from the Morrison Formation (stratigraphic zones 2-4 and 6) in Colorado and Utah, USA, dating from 145 to 150 million years ago, during the Kimmeridgian to Tithonian stages of the Jurassic period. B. altithorax has relatively shorter limbs and a longer torso than the long-limbed African species. A very complete sauropod skull found in Colorado, previously thought to belong to Apatosaurus and later Camarasaurus, probably belonged to B. altithorax. It may have been more primitive than other brachiosaurs, an intermediate form between camarasaur-grade macronarians and B. brancai.

 

A second species of Brachiosaurus, B. brancai, was named and described by Janensch in 1914. For nearly a century, this second species represented the best known "type" of Brachiosaurus, as it was known from five partial skeletons, including at least three skulls and some limb bones, which were recovered near Lindi, Tanzania in the early 1900s. It lived at the same time as B. altithorax and resembled its North American cousin in several aspects, including its unusually long front limbs and sloping body. B. brancai was advanced than B. altithorax, had longer limbs, a skull with a taller, shorter nasal arch or "crest," a shorter muzzle, and longer limbs. Due to these differences, Gregory S. Paul suggested in 1998 that it belonged in its own genus, which he named Giraffatitan.

 

Information sourced from Wikipedia