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Temporal range: Late Jurassic, 154–153 Ma
FMNH Brachiosaurus.JPG
Reconstructed skeleton cast at the Field Museum of Natural History
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Order: Saurischia
Suborder: Sauropodomorpha
Clade: Sauropoda
Family: Brachiosauridae
Genus: Brachiosaurus
Riggs, 1903[1]
Species: B. altithorax
Binomial name
Brachiosaurus altithorax
Riggs, 1903[1]

Brachiosaurus /ˌbrækiəˈsɔːrəs/ is a genus of sauropod dinosaur from the Jurassic Morrison Formation of North America. It was first described by American paleontologist Elmer S. Riggs in 1903 from fossils found in the Grand River Canyon (now Colorado River) of western Colorado, in the United States. Riggs named the dinosaur Brachiosaurus altithorax, declaring it "the largest known dinosaur". Brachiosaurus had a disproportionately long neck, small skull, and large overall size, all of which are typical for sauropods. However, the proportions of Brachiosaurus are unlike most sauropods: the forelimbs were longer than the hindlimbs, which resulted in a steeply inclined trunk, and its tail was shorter in proportion to its neck than other sauropods of the Jurassic.

Brachiosaurus is the namesake genus of the family Brachiosauridae, which includes a handful of other similar sauropods. Much of what is known by laypeople about Brachiosaurus is in fact based on Giraffatitan brancai, a species of brachiosaurid dinosaur from the Tendaguru Formation of Tanzania that was originally described by German paleontologist Werner Janensch as a species of Brachiosaurus. Recent research shows that the differences between the type species of Brachiosaurus and the Tendaguru material are significant enough that the African material should be placed in a separate genus. Several other potential species of Brachiosaurus have been described from Africa and Europe, but none of them are thought to belong to Brachiosaurus at this time.

Brachiosaurus is one of the rarer sauropods of the Morrison Formation. The type specimen of B. altithorax is still the most complete specimen, and only a relative handful of other specimens are thought to belong to the genus. It is regarded as a high browser, probably cropping or nipping vegetation as high as possibly 9 metres (30 ft) off of the ground. Unlike other sauropods, and its depiction in the film Jurassic Park, it was unsuited for rearing on its hindlimbs, it has been used as an example of a dinosaur that was most likely ectothermic because of its large size and the corresponding need for forage, but more recent research finds it to have been warm-blooded.


Size compared to a human

Since "Brachiosaurus" brancai (Giraffatitan) is known from much more complete material than B. altithorax, most size estimates for Brachiosaurus are actually for the African taxon. There is an additional element of uncertainty for North American Brachiosaurus because the most complete skeleton appears to have come from a subadult,[2] over the years, the mass of B. altithorax has been estimated as 35.0 metric tons (38.6 short tons),[3] 43.9 metric tons (48.4 short tons),[4] 28.7 metric tons (31.6 short tons)[2] and, most recently, 56.3 metric tons (62.1 short tons).[5] In cases when the authors also provided estimates for Giraffatitan, they found that genus to be somewhat lighter (31.5 metric tons (34.7 short tons) for Paul [1988],[3] 39.5 metric tons (43.5 short tons) for Mazzetta et al [2004],[6] 23.3 metric tons (25.7 short tons) for Taylor [2009],[2] and 34.0 metric tons (37.5 short tons) for Benson et al [2014]).[5] The length of Brachiosaurus has been estimated at 26 metres (85 ft).[7]

Life restoration

Like all sauropod dinosaurs, Brachiosaurus was a quadrupedal animal with a small skull, a long neck, a large trunk with a high-ellipsoid cross section, a long, muscular tail and slender, columnar limbs.[8] Large air sacs connected to the lung system were present in the neck and trunk, invading the vertebrae and ribs, greatly reducing the overall density.[9][10] While the holotype does not include elements of the neck, that of the closely related Giraffatitan was very long even for sauropod standards, consisting of 13 elongated cervical vertebrae.[11] Brachiosaurus likely shared the very elongated neck ribs with Giraffatitan, which run down the underside of the neck, overlapping several other vertebrae. These bony rods were attached to neck muscles at their ends, allowing these muscles to operate distal portions of the neck while itself being located closer to the body, thus lightening the neck,[12][13] the ribcage was unusually deep.[1] Although the humerus (upper arm bone) and femur (thigh bone) were roughly equal in length, the entire forelimb would have been longer than the hindlimb, as can be inferred from the elongated forearm and metacarpus known from other brachiosaurids.[2] This is in contrast to most other sauropods, especially diplodocoids, in which the forearm can be much shorter,[14] the humerus (upper arm bone) of Brachiosaurus was relatively lightly built for its size,[2] measuring 2.04 metres (6.7 ft) in length in the type specimen.[1] The femur (thigh bone) of the type specimen was only 2.03 metres (6.7 ft) long.[1] This lead to the trunk being inclined, with the front much higher than the hips, and the neck exiting the trunk at a steep angle. Overall, this shape resembles a giraffe more than any other living animal.[3]

Brachiosaurus differed in its overall body proportions from the closely related Giraffatitan. The trunk was longer than in the latter genus given its more elongated dorsal (back) vertebrae; this difference had been estimated at 25–30%. Only a single complete caudal (tail) vertebra had been discovered, but its great height indicates that the tail was taller than in Giraffatitan. Furthermore, this vertebrae showed a much greater area for ligament attachment due to the broadened neural spine, indicating that the tail was also longer than in the African taxon, possibly by 20–25%,[2] although Paul, in 1988, suggested that the neck was shorter Brachiosaurus than in Giraffatitan, two cervical vertebrae likely belonging to Brachiosaurus suggest identical proportions.[2][3] Unlike Giraffatitan and other sauropods, which showed vertically oriented forelimbs, Brachiosaurus appears to have been slightly sprawled at the shoulder joint, as indicated by the sidewards orientation of the joint surface of the coracoid.[2] The humerus was less slender than that of Giraffatitan, while the femur showed similar proportions, this might indicate that the forelimbs of Brachiosaurus supported a greater fraction of the body weight than is the case for Giraffatitan.[2]


Reconstruction of the Felch Quarry skull, Denver Museum of Nature & Science. The fleshy nostril would have been placed at the front of the demarcated nasal fossa

Though no skull remains were discovered with the original Brachiosaurus skeleton, one partial skull found at a different location, referred to as the Felch Quarry skull (specimen USNM 5730), may belong to Brachiosaurus, since there is no overlapping material between the two specimens, the skull has only been assigned to B. sp. (of uncertain species). As reconstructed, the skull was about 81 centimeters (2.66 ft) long from the occipital condyle at be the back of the skull to the front of the premaxillae (the front bones of the upper jaw), making it the largest sauropod skull known from the Morrison Formation. It appears to have been most similar to and intermediate between that of Giraffatitan and Camarasaurus. Overall, the skull was tall as in Giraffatitan, with a snout that was long (about 36% of the skull length) in front of the nasal bar between the nostrils, which is typical of brachiosaurids, the snout was set at an angle relative to the rest of the skull, which gave the impression that the snout pointed downwards. The frontal bones on top of the skull were short and wide (similar to Giraffatitan), fused together, and connected by a suture to the parietal bones, which were also fused together. Combined, the frontoparietals were wider than long on the midline, with a suture that extended jaggedly across the skull, the surface of the parietals between the supratemporal fenestrae (openings at the rear skull roof) was wider than that of Giraffatitan, but narrower than that of Camarasaurus. The supratemporal fenestrae were triangular in shape, and almost twice as wide as they were long, the skull differed from that of Giraffatitan in having a U-shaped (instead of W-shaped) suture between the frontal and nasal bones, enhanced by the frontal bones extending forwards over the orbits (eye sockets).[15]

Most of the bones that formed the rear part of the skull were fused together, which obliterated the sutures, apart from that between the parietal and supraoccipital bones. Similar to Giraffatitan, the neck of the occipital condyle was very long, the premaxilla appears to have been longer than that of Camarasaurus, sloping more gradually towards the nasal bar, which created the very long snout. Brachiosaurus had a long and deep maxilla (the main bone of the upper jaw), which was thick along the margin where the alveoli (tooth sockets) were placed, thinning upwards. The interdental plates of the maxilla were thin, fused, porous, and triangular. There were triangular nutrient foramina between the plates, each containing the tip of an erupting tooth, it differed from the skull of Giraffatitan, but was similar to Camarasaurus, in having much larger maxillary fenestrae. The narial fossa (depression) in front of the bony nostril was long and contained a subnarial fenestra, which was much larger than those of Giraffatitan and Camarasaurus, the dentaries (the bones of the lower jaws that contained the teeth) were robust, though less than in Camarasaurus. The mandibular symphysis (where the two dentaries connected at the front of the mandible) interlocked with a weak tongue and groove, the upper margin of the dentary was arched in profile, but not as much as in Camarasaurus. The interdental plates of the dentary were somewhat oval, with diamond shaped openings between them, the dentary had a Meckelian groove which was open until below the ninth alveolus, continuing thereafter as a shallow through.[15]

Skull cast of the related Giraffatitan, Natural History Museum, Berlin

Each maxilla had space for about 14 or 15 teeth, whereas Giraffatitan had 11 and Camarasaurus 8 to 10, the maxillae contained replacement teeth with rugose enamel, similar to Camarasaurus, but lacked the small denticles (serrations) along the margins. Since the maxilla was wider than that of Camarasaurus, this indicates that Brachiosaurus had larger teeth, the replacement teeth in the premaxilla had crinkled enamel, and the most complete of these teeth did not have denticles. Each dentary had space for about 14 teeth, the only well preserved tooth of this skull is large, spoon-shaped, and may be from the front part of the left dentary. It differs from those of Giraffatitan in that the crown is much wider than the root, similar to Camarasaurus, that the tooth is not worn implies that it had erupted around the time the animal died. The outer and inner sides of the tooth were crenelated (had indented vertical grooves); the crenelations of one side met with those of the other side at the top of the tooth, where they formed denticles. The maxillary tooth rows of Brachiosaurus and Giraffatitan end well in front of the antorbital fenestra (the opening in front of the orbit), whereas they end just before and below the fenestra in Camarasaurus and Shunosaurus.[15]

Though the bony nasal openings of neosauropods like Brachiosaurus were large and placed on the top of their skulls, the American paleontologist Lawrence M. Witmer pointed out in 2001 that all living vertebrate land animals have their external fleshy nostrils placed to the front of the bony nostril. The fleshy nostrils of such sauropods would have been placed at the front of the narial fossa, the depression which extended far in front of the bony nostril towards the snout. Earlier, the fleshy nostrils of sauropods were thought to have been placed at the back of the bony nostril because these animals were inaccurately thought to have been amphibious, and used their large nasal openings as snorkels when submerged.[16]

History of discovery

Holotype material during excavation

The genus Brachiosaurus, and type species B. altithorax, are based on a partial postcranial skeleton from Fruita, in the valley of the Colorado River of western Colorado.[17] This specimen was collected from rocks of the Brushy Basin Member of the Morrison Formation[18] in 1900 by American paleontologist Elmer S. Riggs and his crew from the Field Columbian Museum (now the Field Museum of Natural History) of Chicago.[1] It is currently cataloged as FMNH P 25107.[2] Riggs and company were working in the area as a result of favorable correspondence between Riggs and S. M. Bradbury, a dentist in nearby Grand Junction; in 1899, Riggs had sent inquiries to rural locations in the western United States concerning fossil finds, and Bradbury, an amateur collector himself, reported that dinosaur bones had been collected in the area since 1885.[17]

Elmer S. Riggs’ preparator, H.W. Menke, lying by a humerus during the excavation in 1900

It was Riggs' field assistant H. W. Menke who found FMNH P 25107,[1] on July 4, 1900.[19] The locality, Riggs Quarry 13, was found on a small hill later known as Riggs Hill; it is marked by a plaque. Additional Brachiosaurus fossils are reported on Riggs Hill, but other fossil finds on the hill have been vandalized.[19][20] Riggs published a short report in 1901, noting the unusual length of the humerus compared to the femur and the extreme overall size and the resulting giraffe-like proportions, as well as the lesser development of the tail, but did not publish a name for the new dinosaur,[21] the titles of Riggs (1901) and (1903) suggested that the specimen was the largest known dinosaur.[1][21] Riggs followed his 1903 publication that named Brachiosaurus altithorax[1] with a more detailed description in a monograph in 1904.[22] Riggs derived the genus name from the Greek brachion/βραχιων meaning "arm" and sauros/σαυρος meaning "lizard", because he realized that the length of the arms was unusual for a sauropod.[1] The species epithet was chosen because of the unusually deep and wide chest cavity, from Latin altus "deep" and Greek thorax/θώραξ (Latin thorax), "breastplate, cuirass, corslet".[23]

Riggs and H.W. Menke working on Brachiosaurus altithorax bones

FMNH P 25107, the holotype of the species B. altithorax, consists of the right humerus (upper arm bone), the right femur (thigh bone), the right ilium (a hip bone), the right coracoid (a shoulder bone), the sacrum (fused vertebrae of the hip), the last seven thoracic (trunk) and two caudal (tail) vertebrae, and a number of ribs.[2][1][21] Riggs described the coracoid as from the left side of the body,[1][22][21] but restudy has shown it to be a right coracoid.[2]

Apatosaurus in the Field Columbian Museum (now Field Museum of Natural History) with Brachiosaurus holotype and other dinosaur bones in glass cases in the background, 1909

Preparation of P 25107, the holotype of Brachiosaurus, began in the fall of 1900 shortly after it was collected by Riggs for the Field Museum of Natural History (Chicago). As the preparation of each bone was finished, it was put on display in a glass case in Hall 35 of the Fine Arts Palace of the Worlds Columbian Exposition, Field Museum's first home. All the bones were on display by 1908 when Field Museum's newly mounted Apatosaurus was unveiled. However, no mount was attempted because only 20% of the skeleton had been recovered; in 1993, the holotype bones were molded and cast, and the missing bones were sculpted based on Giraffatitan material in Berlin. This plastic skeleton was mounted and, in 1994, put on display at the north end of Stanley Field Hall, the main exhibit hall of the Field Museum's current building, the real bones of the holotype were put on exhibit in two large glass cases at either end of the mounted cast. The mount stood until 1999, when it was moved to the B Concourse of United Airlines' Terminal One in O'Hare International Airport to make room for the museum's newly acquired T. rex, "SUE".[24] At the same time, the Field Museum mounted a second plastic cast of the skeleton (designed for outside use) and it has been on display outside the museum on the NW terrace ever since, the only real bones currently on display are the humerus and two dorsals in the Mesozoic Hall of the Field Museum's Evolving Planet exhibit.[25]

In 1969, during a study by Kingham, Brachiosaurus altithorax, along with species now assigned to other genera, were moved from the genus. Kingham found "B." atalaiensis, "B." brancai, and B. altithorax were referable to Astrodon creating many new species of Astrodon apart from the type. Kingham's views of brachiosaurid taxonomy have not been accepted by many authors.[26]

Assigned material

O.C. Marsh's outdated 1896 skeletal reconstruction of Brontosaurus, with skull inaccurately based on that of the Felch Quarry B. sp.

The Fruita skeleton was not the first discovery of Brachiosaurus bones, although it was the first to be recognized as belonging to a new and distinct animal; in 1883, a sauropod skull was found near Garden Park, Colorado, at Felch Quarry 1, and was sent to Othniel Charles Marsh (of "Bone Wars" fame).[2] Marsh incorporated the skull into his skeletal restoration of Brontosaurus,[2][27] it eventually became part of the collections of the National Museum of Natural History, as USNM 5730.[2] In the 1970s, when Jack McIntosh and David Berman were working on the issue of the true skull of Apatosaurus, they reevaluated the Garden Park skull as more similar to Camarasaurus,[28] it was described and recognized as a Brachiosaurus skull in 1998 by the American paleontologists Kenneth Carpenter and Virginia Tidwell, who had earlier made a reconstruction of it, based on casts.[15] Because there are no overlapping parts between this skull and FMNH P 25107, it cannot be confidently assigned to a species,[2][15] so it is classified as Brachiosaurus sp.[15]

Scapulocoracoid originally assigned to Ultrasauros, now assigned to Brachiosaurus, Museum of Ancient Life

Additional discoveries of Brachiosaurus material in North America have been uncommon and consist of a handful of bones. Material has been described from Colorado,[2][29][30][31] Oklahoma,[2][32] Utah,[2][29] and Wyoming,[2][4] and undescribed material has been mentioned from several other sites.[2][18] One of these specimens, a shoulder blade from Dry Mesa Quarry, Colorado, is one of the specimens at the center of the Supersaurus/Ultrasauros issue of the 1980s and 1990s. In 1985, James A. Jensen described disarticulated sauropod remains from the quarry as belonging to several taxa, including the new genera Supersaurus and Ultrasaurus,[33] the latter renamed Ultrasauros shortly thereafter because another sauropod already had the name.[34] Later study showed that the "ultrasaur" material mostly belonged to Supersaurus, although the shoulder blade did not, because the holotype of Ultrasauros, a back vertebra, was one of the specimens that was actually from Supersaurus, the name Ultrasauros is a synonym of Supersaurus. The shoulder blade is now assigned to Brachiosaurus, but the species is uncertain;[2][30] in addition, the Dry Mesa "ultrasaur" was not as large as had been thought; the dimensions of the shoulder's coracoid bone indicate that the animal was smaller than Riggs' original specimen of Brachiosaurus.[2]

Referred front limb bone (humerus) from Potter Creek, USNM 21903

Taylor (2009) lists a number of specimens referred to Brachiosaurus, these include some material, e.g., a humerus from Potter Creek and some Dry Mesa material (the latter partly described as Ultrasauros by Jensen), that are either clearly not brachiosaurid in origin, or at least not clearly referable to Brachiosaurus.[2] In contrast, a cervical (neck) vertebra and the skull mentioned above may belong to either B. altithorax or an as-yet unknown brachiosaurid from North America.[2] The cervical was found near Jensen, Utah, by Jensen,[29] and – if it belongs to Brachiosaurus – is one of a handful of neck vertebrae known for American brachiosaurids.[2] There is no unambiguous material of the skull, neck, anterior dorsal (forward trunk) region, distal (lower) limbs or feet.[2] More recently, Carballido et al. (2012) reported on a nearly complete postcranial skeleton of a juvenile sauropod (approximately 2 metres (6.6 ft) long) from the Morrison Formation of the Bighorn Basin, north-central Wyoming. This specimen was originally thought to belong to a diplodocid, but the authors reinterpreted it as representing a brachiosaurid, probably Brachiosaurus altithorax.[35]

Formerly assigned species

Skeleton of Giraffatitan, formerly B. brancai, Berlin

When describing the brachiosaurid material from Tendaguru in 1914, Janensch listed a number of differences and commonalities between them and B. altithorax.[36] In three further publications in 1929,[37] 1950 [38] and 1961[39] Janensch compared the two species in more detail, listing 13 putative shared characters.[2] Of these, however, only four appear to be valid, while six pertain to more inclusive groups than Brachiosauridae, and the rest are either difficult to assess or refer to material that is not Brachiosaurus.[2]

There was ample material referred to "B." brancai in the collections of the Museum für Naturkunde Berlin, some of which was destroyed during World War II. Other material was transferred to other institution throughout Germany, some of which was also destroyed. Additional specimens are likely among the material collected by the British Museum of Natural History's Tendaguru expedition.[40] Much or all of this material probably belongs to Giraffatitan, although some may represent a new brachiosaurid.[41]

Janensch based his description of "B." brancai on "Skelett S" (skeleton S) from Tendaguru,[36] but later realized that it comprised two partial individuals: S I and S II.[37] He at first did not designate them as a syntype series, but in 1935 made S I (MB.R.2180) the lectotype. Taylor in 2009, unaware of this action, proposed the larger and more complete S II (MB.R.2181) as the lectotype.[2] It includes, among other bones, several dorsal (trunk) vertebrae, the left scapula, both coracoids, both sternals (breastbones), both humeri, both ulna and radii (lower arm bones), a right hand, a partial left hand, both pubes (a hip bone) and the right femur, tibia and fibula (shank bones). Later Taylor realised that Janensch had in 1935 designated the smaller skeleton S I as the lectotype.[42][43] A reassessment of the relation between the African and American brachiosaur material indicates that a separate generic name is warranted for the Tendaguru material, so "B." brancai has been moved to its own genus: Giraffatitan.[2][3] "B." fraasi was erected by Janensch in 1914, but later synonymized with "B." brancai;[37] this material now belongs to Giraffatitan.[2]

In 1988, Gregory Paul published a new reconstruction of the skeleton of "B." brancai, highlighting a number of differences in proportion between it and B. altithorax. Chief among them is a difference in the way the trunk vertebrae vary: they are fairly uniform in B. altithorax, but vary widely in the African material. Paul believed that the limb and girdle elements of both species were very similar, and therefore suggested to separate them not at genus, but only at subgenus level.[3]

Giraffatitan was raised to genus level by Olshevsky without comment.[34] A detailed study of all material, including the limb and girdle bones, by Michael Taylor in 2009 found that there are significant differences between Brachiosaurus altithorax and the Tendaguru material in all elements known from both species. Taylor found 26 distinct osteological (bone-based) characters, a larger difference than that between, e.g., Diplodocus and Barosaurus, and therefore argued that the African material should be placed in its own genus—Giraffatitan—as G. brancai.[2] An important difference between the two genera is the overall body shape, with Brachiosaurus having a 23% longer dorsal (trunk) vertebrate series and a 20 to 25% longer and also taller tail.[2]

Originally described by de Lapparent and Zbyszewski,[44], "B." atalaiensis' reference to Brachiosaurus was doubted by Upchurch, Barret and Dodson,[8] who listed it as an unnamed brachiosaurid, and placed in its own genus Lusotitan by Antunes and Mateus.[45] De Lapparent and Zbyszewski described a series of remains but did not designate a type specimen. Antunes and Mateus selected a partial postcranial skeleton (MIGM 4978, 4798, 4801–4810, 4938, 4944, 4950, 4952, 4958, 4964–4966, 4981–4982, 4985, 8807, 8793–87934) as a lectotype; this specimen includes 28 vertebrae, chevrons, ribs, a possible shoulder blade, humeri, forearm bones, partial left pelvis, lower leg bones, and part of the right ankle. The low neural spines, the prominent deltopectoral crest of the humerus (a muscle attachment site on the upper arm bone), the elongated humerus (very long and slender), and the long axis of the ilium tilted upward indicate that Lusotitan is a brachiosaurid.[45]

Diagram showing preserved parts of the "B." nougaredi sacrum in blue

The species "B." nougaredi is known from fragmentary remains discovered in eastern Algeria, in the Sahara Desert. The present type material consists of a sacrum and some of the left metacarpals and phalanges. Found at the discovery site but not collected were partial bones of the left forearm, wrist bones, a right shin bone, and fragments that may have come from metatarsals.[46] Albert-Félix de Lapparent, who described and named the material in 1960, reported the discovery locality as being in the Late Jurassic–age Taouratine Series (he assigned the rocks this age in part because of the presumed presence of Brachiosaurus),[46] but more recent review assigns it to the "Continental intercalaire," which is considered to be of Albian age (late Early Cretaceous, significantly younger).[8]

"B." nougaredi was formerly considered to be a species of Brachiosaurus,[46] or a distinct, unnamed brachiosaurid,[8] but a more recent analysis finds that the remains probably belong to more than one species.[47] The metacarpals were found to belong to an indeterminate Titanosauriform, because the sacrum's current location is unknown, it was not analyzed and considered an indeterminate sauropod until its rediscovery. Only four out of the five sacral vertebrae are preserved, but the preserved portion alone measures 1.3 metres (4.3 ft) long, larger than any other sauropod sacrum ever found, except Argentinosaurus and Apatosaurus.[47]


Brachiosaurus was originally classified as a generic sauropod by Riggs, as not enough material was known to compare it properly to Camarasaurus, Apatosaurus, or Atlantosaurus.[1] In 1904, Riggs described more of the holotype material of Brachiosaurus, and decided that it was more closely related to Haplocanthosaurus than any other sauropod known from the Morrison Formation, because of the significant differences from other taxa, Riggs named the family Brachiosauridae, of which Brachiosaurus is the namesake genus.[22] Over the years, a number of sauropods have been assigned to Brachiosauridae, such as Astrodon, Bothriospondylus, Dinodocus, Pelorosaurus, Pleurocoelus, and Ultrasaurus,[48] but most of these are currently regarded as dubious or of uncertain placement.[8] A phylogenetic analysis of sauropods published in the description of Abydosaurus found that genus to form a clade with Brachiosaurus and Giraffatitan (included in Brachiosaurus).[49] A more recent analysis focused on possible Asian brachiosaurid material found a clade including Abydosaurus, Brachiosaurus, Cedarosaurus, Giraffatitan, and Paluxysaurus, but not Qiaowanlong, the putative Asian brachiosaurid.[50] Related genera include Lusotitan and Sauroposeidon.[8] Brachiosauridae is situated at the base of Titanosauriformes, a group of sauropods that also includes the titanosaurs.[50]

Reconstructed skeleton in O'Hare International Airport

According to the revised diagnosis by Taylor, Brachiosaurus altithorax is diagnosed by a plethora of characters, many to be found on the dorsal (back) vertebrae,[2] among the characters placing it in the family Brachiosauridae are a ratio of humerus length to femur length of at least 0.9 (i.e. the upper arm bone is at least nearly as long as the thigh bone), and a very flattened femur shaft (ratio ≥1.85).[2]

Cladogram of Brachiosauridae after D'Emic (2012).[26]









Neck posture and movement

Restoration showing the neck pointing upwards

Historically, reconstructions of the neck positions of Brachiosaurus have varied from fairly low to nearly vertical. More recent studies have favored an upward posture. Studies by Christian and Heinrich (1998), Christian (2002) and Christian and Dzemski (2007) examined the compressive forces on the interlocking joints of the cervical vertebrate of Giraffatitan and concluded that they were consistent with the animal habitually holding its head nearly vertically with its center of mass located above the base of the neck. In addition, the neck was likely formed an S-shape most of the time. Brachiosaurids could have adapted a more horizontal posture but only for a short periods of time.[51][52][12]

Further evidence for the vertical posture of the neck can be found in the front limbs which were longer than the hind limbs and thus would have likely given the neck further elevation,[12][53] with their heads held high above the heart, brachiosaurids would have had stressed cardiovascular systems. It is estimated that the heart of Brachiosaurus would have to pump double the blood pressure of a giraffe to reach the brain, and possibly weighed 400 kg (880 lb).[53] However, an S-curvature of the neck could have reduced distance between the brain and heart by 2 m (6 ft 7 in) in comparison to a totally vertical posture.[12]

The flexibility of the neck of sauropods has been debated. Mobility was reconstructed as quite low by Stevens and Parrish.[54][55][56] while other researchers like Paul and Christian and Dzemski argued for more flexible necks.[3][57] In studying the inner ear of Giraffatitan, Gunga & Kirsch (2001) concluded that brachiosaurids moved their necks in lateral directions.[58][12]

Feeding and diet

Assigned neck vertebra, BYU Museum of Paleontology

Brachiosaurus is thought to have been a high browser, feeding on foliage well above the ground. Even if it did not hold its neck near vertical, and instead had a straighter neck, its head height may still have been over 9 metres (30 ft) above the ground.[59][4] It probably fed mostly on foliage above 5 metres (16 ft). This does not preclude the possibility that it also fed lower at times, between 3 to 5 metres (9.8 to 16.4 ft) up.[59] Its diet likely consisted of ginkgos, conifers, tree ferns, and large cycads, with intake estimated at 200 to 400 kilograms (440 to 880 lb) of plant matter daily.[59] However, more recent studies estimate that ~240 kilograms (530 lb) of plant matter would have been sufficient to feed a 70 metric tons (77 short tons) sauropod,[60] so Brachiosaurus may have required only about 120 kilograms (260 lb) of fodder a day. Brachiosaur feeding involved simple up–and–down jaw motion, the teeth were arranged to shear material as they closed, and were probably used to crop and/or nip vegetation.[61]

It has repeatedly been suggested, e.g. in the movie Jurassic Park, that Brachiosaurus could rear into a bipedal or tripodal (with tail support) pose to feed.[3] However, a detailed physical modelling-based analysis of sauropod rearing capabilities by Heinrich Mallison showed that while many sauropods could rear, the unusual brachiosaurid body shape and limb length ratio made them exceptionally ill suited for rearing, the forward position of the center of mass would have led to problems with stability, and required unreasonably large forces in the hips to obtain an upright posture. Brachiosaurus would also have gained relatively little from rearing (only 33% more feeding height), compared to other sauropods, for which a bipedal pose may have tripled the feeding height.[62]


Like all sauropods, Brachiosaurus was homeothermic (maintaining a stable internal temperature) and endothermic (controlling body temperature through internal means), meaning that it was able to actively control its body temperature ("warm-blooded"), producing the necessary heat through a high basic metabolic rate of its cells.[63] In the past, Brachiosaurus has been used an example of a dinosaur for which endothermy is unlikely, because of the combination of great size (leading to overheating) and great caloric needs to fuel endothermy.[64] However, these calculations were based on incorrect assumptions about the available cooling surfaces (the large air sacs were not known), and a grossly inflated body mass, these inaccuracies resulted in the overestimation of heat production and the underestimation of heat loss.[63] The large nasal arch has been postulated as an adaptation for cooling the brain, as a surface for evaporative cooling of the blood.[64]


Juvenile Brachiosaurus sp. specimen SMA 0009 (the skull is reconstructed)

With the removal of the East African Giraffatitan, Brachiosaurus is known only from the Morrison Formation of western North America.[2] The Morrison Formation is interpreted as a semiarid environment with distinct wet and dry seasons,[65][66] and flat floodplains.[65] Vegetation varied from gallery forests (river–lining forests in otherwise treeless settings) of conifers, tree ferns, and ferns, to fern savannas with rare Araucaria-like trees.[67] Several other sauropod genera were present in the Morrison Formation, with differing body proportions and feeding adaptations,[4] among these were Apatosaurus, Barosaurus, Camarasaurus, Diplodocus, Haplocanthosaurus, and Supersaurus.[4][68] Brachiosaurus was one of the less abundant Morrison Formation sauropods. In a survey of over 200 fossil localities, John Foster reported 12 specimens of the genus, comparable to Barosaurus (13) and Haplocanthosaurus (12), but far fewer than Apatosaurus (112), Camarasaurus (179), and Diplodocus (98).[4] Brachiosaurus fossils are found only in the lower-middle part of the expansive Morrison Formation (stratigraphic zones 2–4), dated to about 154-153 million years ago,[69] unlike many other types of sauropod which have been found throughout the formation.[4]

The Morrison Formation records an environment and time dominated by gigantic sauropod dinosaurs.[70] Other dinosaurs known from the Morrison include the theropods Koparion, Stokesosaurus, Ornitholestes, Ceratosaurus, Allosaurus and Torvosaurus, the sauropods Apatosaurus, Camarasaurus, and Diplodocus, and the ornithischians Camptosaurus, Dryosaurus, Othnielia, Gargoyleosaurus and Stegosaurus.[71] Diplodocus is commonly found at the same sites as Apatosaurus, Allosaurus, Camarasaurus, and Stegosaurus.[72] Allosaurus, which accounting for 70 to 75% of theropod specimens and was at the top trophic level of the Morrison food web.[73] Many of the dinosaurs of the Morrison Formation are the same genera as those seen in Portuguese rocks of the Lourinha Formation (mainly Allosaurus, Ceratosaurus, Torvosaurus, and Stegosaurus), or have a close counterpart (Brachiosaurus and Lusotitan, Camptosaurus and Draconyx).[74] Other vertebrates that shared this paleoenvironment included ray-finned fishes, frogs, salamanders, turtles like Dorsetochelys, sphenodonts, lizards, terrestrial and aquatic crocodylomorphans such as Hoplosuchus, and several species of pterosaur like Harpactognathus and Mesadactylus. Shells of bivalves and aquatic snails are also common, the flora of the period has been revealed by fossils of green algae, fungi, mosses, horsetails, cycads, ginkgoes, and several families of conifers. Vegetation varied from river-lining forests of tree ferns, and ferns (gallery forests), to fern savannas with occasional trees such as the Araucaria-like conifer Brachyphyllum.[75]

Cultural significance

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.[76][77] 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.[78]


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External links