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Old Brachiosaurus article in full

Brachiosaurus, meaning "arm lizard", from the Greek brachion/βραχίων meaning "arm" and sauros/σαῦρος meaning "lizard", is a genus of 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, one of a group of four-legged, plant-eating dinosaurs with long necks and tails and relatively small brains. 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 definitively identified until 1998, when Carpenter and Tidwell re-described a skull in 1883 discovered by Marshall P. Felch, a collector working for Othniel Charles Marsh. Already in 1935 Werner Janensch had suggested the skull belonged to Brachiosaurus altithorax. 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
Many 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 t, compared to 23.3 t 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.

Discovery and species
The first Brachiosaurus specimen was discovered in 1900 by Elmer Riggs, 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." The original specimen (holotype) of B. altithorax includes a sequence of seven posterior dorsal vertebrae, sacrum, proximal caudal vertebra, coracoid, humerus, femur and ribs.

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. A very complete sauropod skull found in Colorado may belong to B. altithorax.

Giraffatitan
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 much more complete material: five partial skeletons, including at least three skulls and some limb bones. It lived at approximately the same time as B. altithorax and resembled its North American cousin in several aspects, including its unusually long front limbs and sloping body. Compared to B. altithorax, though, B. brancai had longer limbs, a skull with a taller, shorter nasal arch or "crest," trunk vertebrae with different proportions and a shorter muzzle.

In 1988, Gregory S. Paul published on some of these differences, finding them significant enough to establish a subgenus for B. brancai: Brachiosaurus (Giraffatitan) brancai. In 1991, George Olshevsky asserted that these differences are enough to place the African brachiosaurid in its own genus, Giraffatitan. Further differences between the North American and African forms came to light with the description in 1998 of a North American brachiosaurid skull. This skull, which had been found nearly a century earlier (it is the skull Marsh used on his early reconstructions of Brontosaurus), was identified as "Brachiosaurus sp.". The skull is more camarasaur-like than the distinctive high-crested skull of B. brancai.

This classification was not widely followed by other scientists as it was not supported by a rigorous comparison of both species. However, a detailed comparison was conducted by Michael Taylor in 2009. Taylor showed that "Brachiosaurus" brancai differed from B. altithorax in almost every fossil bone that could be compared, in terms of both size, shape, and proportion, finding that the placement of Giraffatitan in a separate genus was valid.

Additional species
An additional species, B. alataiensis, was described by de Lapparent and Zbyszewski in 1957, for back bones (vertebrae) and parts of the hip and limbs, which were recovered in Estremadura, Portugal (dating to about 150 million years ago, during the Kimmeridgian stage of the Late Jurassic). B. alataiensis was reclassified as the new genus Lusotitan in 2003.

Another possible species is B. nougaredi, named by de Lapparent in 1960. It is known only from set of fused bones over the hip (sacrum) and parts of a forelimb, which were recovered in Wargla, Algeria. It lived 112 million years ago, during the early Albian age of the early Cretaceous period. Due to its fragmentary nature and much later time period than Brachiosaurus altithorax, it is considered dubious and may not belong to Brachiosaurus.

Environment and behavior
Brachiosaurus is one of the largest known dinosaurs of the Jurassic. It lived on prairies filled with ferns, bennettites and horsetails, and it moved through vast conifer forests and groves of cycads, seed ferns and ginkgos. Contemporary genera included Stegosaurus, Dryosaurus, Apatosaurus and Diplodocus.

Brachiosaurus nostrils, like the huge corresponding nasal openings in its skull, were long thought to be located on the top of the head. In past decades, scientists proposed that the animal used its nostrils like a snorkel, spending most of its time submerged in water in order to support its great mass. The current consensus view, however, is that Brachiosaurus was a fully terrestrial animal. Studies have demonstrated that water pressure would have prevented the animal from breathing effectively while submerged and that its feet were too narrow for efficient aquatic use. Furthermore, new studies by Lawrence Witmer (2001) show that, while the nasal openings in the skull were placed high above the eyes, the nostrils would still have been close to the tip of the snout (a study which also lends support to the idea that the tall "crests" of brachiosaurs supported some sort of fleshy resonating chamber).

In culture
The original Brachiosaurus specimens collected by Elmer Riggs for the Field Museum of Natural History (Chicago) were not put on display in the museum until 1994, when a skeletal mount (made up of resin casts rather than actual fossil bones) was constructed inside the museum's main Stanley Field Hall. The mount stood until 1999, when it was moved to the B Concourse of United Airlines' Terminal One in O'Hare International Airport. At the same time, a second cast (in bronze) of the Field Museum's B. altithorax was constructed outside the museum.

Brachiosaurus is one of the best-known dinosaurs amongst both paleontologists and the general public. A main belt asteroid,, has been named 9954 Brachiosaurus in honor of the genus. The genus has been featured in many films and television programs, most notably the Jurassic Park and Walking with Dinosaurs series. The digital model of Brachiosaurus used in Jurassic Park went on to become the starting point for the ronto models in the 1997 special edition of the science fiction film Star Wars Episode IV: A New Hope.