Brachiosaurus
| Brachiosaurus Temporal range: Late Jurassic–Early Cretaceous?,
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| Bronze cast of a B. altithorax specimen outside the Field Museum of Natural History | |
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| Genus: | Brachiosaurus Riggs, 1903
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Brachiosaurus (Template:Pron-en), meaning "arm lizard", from the Greek brachion/βραχιων meaning "arm" and sauros/σαυρος meaning "lizard", was 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 freqently in the form of Giraffatitan brancai, which was originally named 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. 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.
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 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.[1]
Size
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.[2]
The original specimens (holotype) of the first known species, B. altithorax, include a sequence of seven posterior dorsal vertebrae, sacrum, proximal caudal vertebra, coracoid, humerus, femur and ribs: enough from which to estimate size.
Based on measurements of comparable bones, Brachiosaurus was similar in overall size to the related Giraffatitan, which is estimated to have attained 25 metres (82 ft) in length and was probably able to raise its head about 13 metres (43 ft) above ground level. However, Brachiosaurus may have been longer, as it had a longer torso and possibly a longer tail than Giraffatitan. No neck material is known from the holotype specimen; however, there are some brachiosaur neck vertebra that have been assigned to Brachiosaurus by some authors. If the vertebrae do belong to Brachiosaurus then they suggest that it had a similarly proportioned neck to Giraffatitan. Additionally, the best known Brachiosaurus specimen was not fully grown when it died, meaning it may have had an adult length of over 25 m. Brachiosaurus was also stockier, and therefore likely heavier, than Giraffatitan. Brachiosaurus is estimated to have weighed 28.7 tonnes (28.2 long tons; 31.6 short tons), compared to 23.3 tonnes (22.9 long tons; 25.7 short tons) for Giraffatitan.[2]
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."[3] 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.[4] 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.[1]
Giraffatitan
A second species of Brachiosaurus, B. brancai, was named and described by Janensch in 1914.[5] 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.
In 1988, Gregory S. Paul noted that the African form (on which most popular depictions of Brachiosaurus are based) showed significant differences from the North American form (B. altithorax), especially in the proportions of its trunk vertebrae and in its more gracile build. Paul used these differences to create a subgenus he named Brachiosaurus (Giraffatitan) brancai. In 1991, George Olshevsky asserted that these differences are enough to place the African brachiosaurid in its own genus, simply Giraffatitan.[6]
Adding further differences between the two species was 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), is identified as "Brachiosaurus sp." and may well belong to B. altithorax. The skull is more camarasaur-like than the distinctive high-crested skull of B. brancai.[1]
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.[2]
A famous specimen of Giraffatitan brancai (which continues to be labeled Brachiosaurus), mounted in Museum für Naturkunde Berlin, is one of the largest mounted skeletons in the world.
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). However, B. alataiensis was reclassified as the new genus Lusotitan in 2003.[8]
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 the other two Brachiosaurus species, it is considered nomen dubium (dubious name) and may not belong to Brachiosaurus.
Paleobiology
Metabolism
If the Brachiosaurus was endothermic (warm-blooded), it would have taken an estimated ten years to reach full size, if it were instead poikilothermic (cold-blooded), then it would have required over 100 years to reach full size.[9] As a warm-blooded animal, the daily energy demands of Brachiosaurus would have been enormous; it would probably have needed to eat more than ~182 kg (400 lb) of food per day. If Brachiosaurus was fully cold-blooded or was a passive bulk endotherm, it would have needed far less food to meet its daily energy needs. Some scientists have proposed that large dinosaurs like Brachiosaurus were gigantotherms.[10]
Environment and behavior
Brachiosaurus was one of the largest dinosaurs of the Jurassic era; 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. While it is speculated that groups of Brachiosaurus moved in herds, fully grown individuals had little to fear from even the largest predators of the time, Allosaurus and Torvosaurus, on account of their sheer size.
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 theorized 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.[11] At the same time, a second cast (in bronze) of the Field Museum's B. altithorax was constructed outside the museum.[12]
Brachiosaurus is one of the best-known dinosaurs amongst both paleontologists and the general public. A main belt asteroid, 1991 GX7, has been named 9954 Brachiosaurus in honor of the genus.[13][14] 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.[15]
References
- ^ a b c Carpenter, K. and Tidwell, V. (1998). "Preliminary description of a Brachiosaurus skull from Felch Quarry 1, Garden Park, Colorado." Pp. 69–84 in: Carpenter, K., Chure, D. and Kirkland, J. (eds.), The Upper Jurassic Morrison Formation: An Interdisciplinary Study. Modern Geology, 23(1-4).
- ^ a b c Taylor, M.P. (2009). "A Re-evaluation of Brachiosaurus altithorax Riggs 1903 (Dinosauria, Sauropod) and its generic separation from Giraffatitan brancai (Janensh 1914)." Journal of Vertebrate Paleontology, 29(3): 787-806.
- ^ Riggs, E.S. (1903). "Brachiosaurus altithorax, the largest known dinosaur." American Journal of Science, 4(15): 299-306.
- ^ Foster, J. (2007). "Appendix." Jurassic West: The Dinosaurs of the Morrison Formation and Their World. Indiana University Press. pp. 327-329.
- ^ Janensch, W. (1914). "Übersicht über der Wirbeltierfauna der Tendaguru-Schichten nebst einer kurzen Charakterisierung der neu aufgefuhrten Arten von Sauropoden." Archiv fur Biontologie, 3: 81–110.
- ^ Glut, D.F. (1997). "Brachiosaurus". Dinosaurs: The Encyclopedia. McFarland & Company. p. 218. ISBN 0-89950-917-7.
- ^ http://books.google.dk/books?id=CLEPeg_SjTcC&pg=PA69&lpg=PA69&dq=brachiosaurus+Felch+Quarry&source=bl&ots=mmGl4fq-dE&sig=qXGX2ckpINYQoLaM3QQ3pbehaqo&hl=da&ei=gSDCSrzKLobM-QaW44XvCw&sa=X&oi=book_result&ct=result&resnum=8#v=onepage&q=brachiosaurus%20Felch%20Quarry&f=false
- ^ Antunes, M. (2003). "Dinosaurs of Portugal". Comptes rendus. Palévol. 2 (1): 77–95. doi:10.1016/S1631-0683(03)00003-4.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ Case, T.J. (1978). "Speculations on the Growth Rate and Reproduction of Some Dinosaurs". Paleobiology. 4 (3): 323.
- ^ Bailey, J.B. (1997). "Neural spine elongation in dinosaurs: Sailbacks or buffalo-backs?" Journal of Paleontology, 71(6): 1124-1146.
- ^ "Expect Awe-Struck Travelers" (Press release). The Field Museum. November 26, 1999. Retrieved 2009-08-27.
- ^ The Field Museum. "Captions from Selected Historical Photographs (caption number GN89396_52c)." The Field Museum Photo Archives. pdf link. Accessed 2009-Aug-27.
- ^ "JPL Small-Body Database Browser: 9954 Brachiosaurus (1991 GX7)". NASA. Retrieved 2007-04-28.
- ^ Williams, G. "Minor Planet Names: Alphabetical List". Smithsonian Astrophysical Observatory. Retrieved 2007-02-10.
- ^ "Ronto". Databank. Star Wars.com. Retrieved 2009-01-13.
External links
- Expect awe-struck travelers, from the Field Museum. (O'Hare airport mount)
- Dinosaurier-Web, Description and printable fact-sheet with picture (in German and English)
- Benes, Josef. Prehistoric Animals and Plants: old-fashioned illustration of Brachiosaurus, bottom left.
- Why was Brachiosaurus that big? Short summary of a peer review paper
- Brachiosaurus at DinoData
- dB Brachiosaurus (Natural History Museum)
