Brachiosaurus is a sauropod dinosaur genus which lived in the Late Jurassic period (approximately 154-153 million years ago), in North America. This dinosaur was described by Elmer E. Riggs in 1903, based on a fossil postcranial skeleton from the valley of the Colorado River near Fruita, in Colorado, United States. The type species, described by Riggs, is Brachiosaurus altithorax; the name Brachiosaurus means 'arm lizard', which refers to the longer forelegs of the dinosaur; the meaning ot the specific name altithorax is 'deep chest'. Brachiosaurus fossils are rare compared to other dinosaurs, and most of the material assigned to this species consist of only a few bones. Besides the type specimen, further material were found in Colorado, Oklahoma, Utah and Wyoming in the United States. One partially skull is known from Garden Park, Colorado, found by Marshall Parker Fletch in 1883. This skull was about 81 centimeters long, which menas that it is the largest known sauropod skull from the entire Morrison Formation. In 2012, the postcranial skeleton of a young specimen was also discovered in the Morrison Formation, Wyoming; this specimen could be approximately 2 meters long.
Known occurrences of Brachiosaurus altithorax fossils.
Depiction of Brachiosaurus altithorax sp. By Nobu Tamura (http://spinops.blogspot.com) - Own work, CC BY 2.5, https://commons.wikimedia.org/w/index.php?curid=19462825
Valid and formerly assigned species
Though there were several species assigned to Brachiosaurus earlier, now Brachiosaurus altithorax is the sole species of the genus. Brachiosaurus brancai and B. fraasi were described from the Tendaguru Formation, East Africa, by the German paleontologist Werner Janensch in 1914. However, Janensch later synonymised B. fraasi with B. brancai. Due to the vertebral variation between B. altithorax and B. brancai, a separate genus was created for B. brancai in 1991 and the species is known as Giraffatitan brancai yet. Brachiosaurus atalaiensis was described from Portugal by Albert-Félix de Lapparent and Georges Zbyszewski in 1957. This species was also placed to its own genus Lusotitan by Miguel Telles Antunes and Octávio Mateus in 2003. Brachiosaurus nougaredi was described from Algeria by Albert-Félix de Lapparent in 1960, based on fragmentary fossil remains. This species is considered to represent a separated brachiosaurid genus, which is unnamed yet.
Description and anatomy
The size and body mass of Brachiosaurus altithorax are estimated based on the related Giraffatitan brancai, as the fossil material of this species is much more complete and allows us making more accurate evaluations. The length of Brachiosaurus was probably between 18 and 21 meters, its height was about 12-13 meters, and it weighted between 28.3 and 58 metric tons. Brachiosaurus was a quadrupedal dinosaur, with a small head, a long neck, columnar limbs, and had enormous body size. However, unlike other sauropods, the forelimbs of Brachiosaurus were longer than its hindlimbs, which resulted that the shoulder was much higher than the hips; coherently, it had a relatively shorter tail and a steeply inclined trunk. It had large air sacks in the neck and the trunk connected to its lungs. These air sacks also incursed to the vertebrae and the ribs, and therefore reduced the overall density of this dinosaur's body. The neck consisted of thirteen elongated vertebrae, and based on a 2007 analysis based on Preuschoft method to deduce the pattern of stress in the joints between the vertebral centra along the neck, probably it was held in a slight S-curve, with a bent lower and upper sections, and the middle section held straight. It is also supposed that brachiosaurid dinosaurs had a small shoulder hump on the back, as the sideward- and upward-directed vertebral processes were longer between the third and fifth dorsal vertebrae. This structure could provide additional basis for the neck muscles which needed to be quite strong. All in all, the overall body structure of Brachiosaurus and all related brachiosaurid dinosaurs resemble a today's giraffe. The single caudal vertebra of Brachiosaurus suggests that it had a 20-25% longer than in Giraffatitan. An other difference between these two dinosaurs, that the forelegs of Brachiosaurus probably have been slightly sprawled at the shoulder joints, while the arms of Giraffatitan were vertically oriented. Furthermore, in Brachiosaurus the vertebrae of the anterior part of the back coloumn were a bit taller and much longer than those of the posterior part of the back coloumn, while in Giraffatitan the anterior back vertebrae were slightly longer but much taller. An other difference between the two genera is that while in Brachiosaurus caudal ribs were projected laterally, in Giraffatitan they weren't, but they were tilted backwards. The skull of Brachiosaurus had a bump at its foreheadn which made it tall, and had a long snout, with nostrils at the anterior part. It also had a long and deep maxilla, each having space for roughly 14-15 teeth, and also had replacement teeth.
Reconstruction od Brachiosaurus altithorax. By Charles Nye - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=89144210
Brachiosaurus altithorax skeleton. Creator: Valdiney Pimenta - Source: By Matt Wedel - https://svpow.com/2013/08/30/heres-that-brachiosaurus-altithorax-skeleton-you-ordered/, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=71064740
During the nineteenth and early twentieth centuries giant sauropods were considered being too heavy to support their own body mass on land, therefore they must have lived partly submerged in water. Riggs was the first who defended the fully terrestrial adaptation of these dinosaurs. Amongst them, Brachiosaurus shows through its high chest, slender legs, short tail and wide hips a perfect example for the fully terrestrial lifestyle. Though this theory was gradually forgotten during the fist half of the last century, it gained support and became totally accepted since the 1950s.
Brachiosaurus was likely a high browser, which was able cropping the tree's foliage even from as high as 9 meters. The diet of this dinosaur probably included conifers, ginkgos, cycads and tree ferns, and it was estimated that Brachiosaurus needed to consume 200-400 kilograms of plant material per day. During feeding, simply Brachiosaurus moved its jaws up and down, and the swallowed plant material was not well processed orally; therefore, just like other sauropods, Brachiosaurus used hindgut fermentation for making more effective its digestion. As based on fossil records, Brachiosaurus shared its habitat with further sauropods, its specialization for high browsing may have been a result of niche partitioning, which reduced the competition between these different sauropod species. Unlike other sauropod dinosaurs, Brachiosaurus was unable to rear on its hind legs during feeding, due to the forward position of its center of mass. Brachiosaurus was able to lower its head by the downward mobility of the neck, which allowed it to drink for open water. There was a chance, that the fleshly nostrily were retracted towards the top of the head, well above the bony nostrils, which allowed Brachiosaurus to breath while drinking. It is neither excluded, that Brachiosaurus might have had a proboscis, which could have helped the dinosaur to reach higher during feeding (inferred from the enlarged opening for the facial nerve in Giraffatitan).
Skull of Brachiosaurus. By Matt Wedel - https://svpow.com/2011/11/16/sideshow-collectibles-apatosaurus-maquette-part-2-the-head/, CC BY 4.0, https://commons.wikimedia.org/w/index.php?curid=42796873
Similarly to other sauropods, Brachiosaurus was probably "warm-blooded", which means that it could maintain a stable internal body temperature by its own metabolism. Air sacks, which invaded even the bones by their branches, hollowed the skeleton out, which not only made the entire skeleton lighter, but also might have played an important role in thermoregulation by easier removing excess heat.
 Riggs, E.S. (1903): Brachiosaurus altithorax, the largest known dinosaur. American Journal of Science 4. 15 (88): 299-306. doi:10.2475/ajs.s4-15.88.299.
 Taylor, M.P. (2009): A re-evaluation of Brachiosaurus altithorax Riggs 1903 (Dinosauria, Sauropoda) and its generic separation from Giraffatitan brancai (Janensh 1914). Journal of Vertebrate Paleontology, 29 (3): 787-806. doi:10.1671/039.029.0309.
 Carpenter, K.; Tidwell, V. (1998): Preliminary description of a Brachiosaurus skull from Felch Quarry 1, Garden Park, Colorado. Modern Geology. 23 (1-4): 69-84.
 Carballido, J.L.; Marpmann, J.S.; Schwarz-Wings, D.; Pabst, B. (2012): New information on a juvenile sauropod specimen from the Morrison Formation and the reassessment of its systematic position. Palaeontology, 55 (2): 567-582. doi:10.1111/j.1475-4983.2012.01139.x.
 Janensch, W. (1914): Übersicht über der Wirbeltierfauna der Tendaguru-Schichten nebst einer kurzen Charakterisierung der neu aufgefuhrten Arten von Sauropoden [Overview of the vertebrate fauna of the Tendaguru strata along with a brief characterization of the newly listed species of sauropods]. Archiv für Biontologie (in German). 3: 81-110.
 Olshevsky, G. (1991): A revision of the parainfraclass Archosauria Cope, 1869, excluding the advanced Crocodylia. Mesozoic Meanderings. 2: 1-196.
de Lapparent, A.F.; Zbyszewski, G. (1957): Les dinosauriens du Portugal. Mémoire Service Géologique Portugal. 2: 1-63.
 Antunes, M. T.; Mateus, O. (2003): Dinosaurs of Portugal. Comptes Rendus Palevol. 2 (1): 77-95. doi:10.1016/S1631-0683(03)00003-4
de Lapparent, A.F. (1960): "Les dinosauriens du "continental intercalaire" du Sahara central [The dinosaurs of the "continental intercalaire" of the central Sahara]. Mémoires de la Société Géologique de France. Nouvelle Séries (in French). 39 (1-6): 1-57.
 Mannion, P. D.; Upchurch, P.; Barnes, R.N.; Mateus, O. (2013): .Osteology of the Late Jurassic Portuguese sauropod dinosaur Lusotitan atalaiensis (Macronaria) and the evolutionary history of basal titanosauriforms. Zoological Journal of the Linnean Society. 168: 98-206. doi:10.1111/zoj.12029.
 Seebacher, F. (2001): A new method to calculate allometric length-mass relationships of dinosaurs. Journal of Vertebrate Paleontology. 21 (1): 51-60. doi: 10.1671/0272-4634(2001)021[0051:ANMTCA]2.0.CO;2.
 Paul, G.S. (1988): The brachiosaur giants of the Morrison and Tendaguru with a description of a new subgenus, Giraffatitan, and a comparison of the world's largest dinosaurs. Hunteria. 2 (3).
 Benson, R. B. J.; Hunt, G.; Carrano, M.T.; Campione, N.; Mannion, P. (2018): Cope's rule and the adaptive landscape of dinosaur body size evolution. Palaeontology. 61 (1): 13-48. doi: 10.1111/pala.12329.
 Wedel, M.J. (2003): Vertebral pneumaticity, air sacs, and the physiology of sauropod dinosaurs. Paleobiology. 29 (2): 243-255. . doi:10.1666/0094-8373(2003)029<0243:vpasat>2.0.co;2.
 Christian, A.; Dzemski, G. (2007): Reconstruction of the cervical skeleton posture of Brachiosaurus brancai Janensch, 1914 by an analysis of the intervertebral stress along the neck and a comparison with the results of different approaches. Fossil Record. 10 (1): 38-49. doi: 10.1002/mmng.200600017.
 Woodruff, D. C. (2016): Nuchal ligament reconstructions in diplodocid sauropods support horizontal neck feeding postures. Historical Biology. 29 (3): 308-319. doi: doi:10.1080/08912963.2016.1158257.
 Henderson, D.M. (2004): Tipsy punters: sauropod dinosaur pneumaticity, buoyancy and aquatic habits. Proceedings of the Royal Society of London, B. 271 (Suppl 4): S180-S183. doi:10.1098/rsbl.2003.0136.
 Riggs, E.S. (1904): Structure and relationships of opisthocoelian dinosaurs. Part II. The Brachiosauridae. Geological Series (Field Columbian Museum). 2 (6): 229-247.
 Foster, J. (2007): Brachiosaurus altithorax. Jurassic West: The Dinosaurs of the Morrison Formation and Their World. Indianapolis: Indiana University Press. pp. 205-208.
 Sander, P.M.; Christian, A.; Clauss, M.; Fechner, R.; Gee, C.T.; Griebeler, E.-M.; Gunga, H.-C.; Hummel, J.; Mallison, H.; Perry, S.F.; Preuschoft, H.; Rauhut, O.W.M.; Remes, K.; Tütken, T.; Wings, O.; Witzel, U. (2010): Biology of the sauropod dinosaurs: the evolution of gigantism. Biology Reviews. 86 (1): 117-155. doi: 10.1111/j.1469-185X.2010.00137.x.
 Mallison, H. (2011): Rearing Giants - kinetic-dynamic modeling of sauropod bipedal and tripodal poses. In Klein, N., Remes, K., Gee, C. & Sander M. (eds): Biology of the Sauropod Dinosaurs: Understanding the life of giants. Life of the Past (series ed. Farlow, J.). Bloomington, IN: Indiana University Press.
 Knoll, F.; Galton, P. M.; López-Antonanzas, R. (2006). "Paleoneurological evidence against a proboscis in the sauropod dinosaur Diplodocus". Geobios. 39 (2): 215-221. doi:10.1016/j.geobios.2004.11.005.
 Hallett, M.; Wedel, M. (2016): The Sauropod Dinosaurs: Life in the Age of Giants, Baltimore: Johns Hopkins University Press, ISBN 978-1421420288