Temporal range: Late Jurassic, 154–153 Ma
|Reconstructed replica of the holotype skeleton outside the Field Museum of Natural History|
Brachiosaurus // is a genus of sauropod dinosaur that lived in North America during the Late Jurassic, about 154–153 million years ago. 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". The generic name is Greek for "arm lizard", in reference to its proportionately long arms, and the specific name means "deep chest". 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. Most popular depictions of Brachiosaurus are in fact based on Giraffatitan, 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, B. brancai. 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 currently thought to belong to Brachiosaurus.
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 the ground. Unlike other sauropods, 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 sufficient forage, but more recent research finds it to have been warm-blooded.
- 1 Description
- 2 History of discovery
- 3 Classification
- 4 Paleobiology
- 5 Paleoecology
- 6 Cultural significance
- 7 References
- 8 Bibliography
- 9 External links
Most size estimates that have been made for Brachiosaurus are actually based on the related African brachiosaurid Giraffatitan (formerly known as Brachiosaurus brancai), since it is known from much more complete material than Brachiosaurus. There is an additional element of uncertainty for the North American Brachiosaurus because the type (and most complete) specimen appears to represent a subadult, as indicated by the unfused suture between the coracoid, a bone of the shoulder girdle that forms part of the shoulder joint, and the scapula (shoulder blade). Over the years, the mass of B. altithorax has been estimated at 35.0 metric tons (38.6 short tons), 43.9 metric tons (48.4 short tons), 28.7 metric tons (31.6 short tons) and, most recently, 56.3 metric tons (62.1 short tons) and even 58 metric tons (64 short tons). The length of Brachiosaurus has been estimated at 26 meters (85 ft).
While the limb bones of the most complete Giraffatitan skeleton (MB.R.2181) were very similar in size to those of the Brachiosaurus type specimen, the former specimen was found to be somewhat lighter than the Brachiosaurus specimen given its proportional differences. In studies including estimates for both Brachiosaurus and Giraffatitan, the latter was estimated at 31.5 metric tons (34.7 short tons) by Gregory S. Paul in 1988, 39.5 metric tons (43.5 short tons) by Gerardo Mazzetta and colleagues in 2004, 23.3 metric tons (25.7 short tons) by Michael P. Taylor in 2009, and 34.0 metric tons (37.5 short tons) by Roger Benson and colleagues in 2014. Both the Brachiosaurus type specimen and Giraffatitan specimen MB.R.2181, however, likely do not represent the maximum size reached by these genera—while the Brachiosaurus type specimen was probably not fully grown, a fibula referable to Giraffatitan, specimen HM XV2, was with a length of 134 centimetres found to have been 13% longer than that of MB.R.2181.
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. 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. 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 thirteen elongated cervical vertebrae. 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 themselves being located closer to the body, thus lightening the neck. The ribcage was unusually deep. 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. 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. In contrast, most other sauropods show a shorter forelimb than hindlimb; the forelimb is especially short in diplodocoids.
Brachiosaurus differed in its overall body proportions from the closely related Giraffatitan. The trunk was about 25–30% longer than in the latter genus given its more elongated dorsal (back) vertebrae, resulting in a dorsal vertebral column longer than the humerus. Only a single complete caudal (tail) vertebra has been discovered, but its great height indicates that the tail was taller than in Giraffatitan. Furthermore, this vertebra showed a much greater area for ligament attachment due to the broadened neural spine, indicating that the tail was also longer than in Giraffatitan, possibly by 20–25%. Although Paul, in 1988, suggested that the neck was shorter in Brachiosaurus than in Giraffatitan, two cervical vertebrae likely belonging to Brachiosaurus suggest identical proportions. Unlike Giraffatitan and other sauropods, which showed vertically oriented forelimbs, the arm of Brachiosaurus appears to have been slightly sprawled at the shoulder joint, as indicated by the sidewards orientation of the joint surface of the coracoid. 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.
Although the vertebral column of the trunk is incompletely known, Brachiosaurus most likely possessed twelve dorsal vertebrae, as can be inferred from the complete dorsal vertebral column preserved by an unnamed brachiosaurid specimen, BMNH R5937. Vertebrae of the front part of the dorsal column were slightly taller but much longer than those of the back part. This is in contrast to Giraffatitan, where the vertebrae at the front part were only slightly longer but much taller. The centra (vertebral bodies), which form the lower part of the vertebrae, were more elongated than in Giraffatitan and roughly circular in cross-section, while those of the latter genus were broader than tall in cross-section. The foramina (small openings) on the sides of the centra, which allowed for the intrusion of air sacs, were larger than in Giraffatitan. The diapophyses (large projections extending sideways from the neural arch of the vertebrae) were horizontal, while those of Giraffatitan were inclined upwards. At their ends, these processes articulated with the ribs; the articular surface was not distinctly triangular as in Giraffatitan. The upwards projecting neural spines, when seen in side view, stood vertically and were twice as wide at the base than at the top, while those of Giraffatitan were tilted backwards and were not broadened at their base. When seen in front or back view, the neural spines widened towards their tops. In Brachiosaurus, this widening occurred gradually, resulting in a paddle-like shape, while in Giraffatitan the widening occurred abruptly and only in the uppermost portion. At both their front and the back side, the neural spine showed large, triangular rugose surfaces, which were semicircular and much smaller in Giraffatitan. The various processes were connected by thin sheets of bone, the so-called laminae. Brachiosaurus lacked postspinal laminae, which were present in Giraffatitan, running down the back side of the neural spines. The spinodiapophyseal laminae, which stretched from the neural spines to the diapophyses, was conflated with the spinopostzygapophyseal laminae, which stretched between the neural spines and the articular process at the back of the vertebra, and therefore terminated at mid-height of the neural spine. In Giraffatitan, both laminae were not conflated, and the spinodiapophyseal laminae reached up to the top of the neural spine. Three further details of the laminae of the dorsal vertebrae are only known from Giraffatitan, and are absent in other sauropods including Brachiosaurus, adding to the features distinguishing these genera.
Air sacs did not only invade the vertebrae, but also the ribs. In Brachiosaurus, the air sacs invaded through a small opening on the front side of the rib shafts, while in Giraffatitan openings were present on both the front and back sides of the tuberculum, a bony projection articulating with the diapophyses of the vertebrae. Paul, in 1988, stated that the ribs of Brachiosaurus were longer than in Giraffatitan, which was however questioned by Taylor in 2009. Behind the dorsal vertebral column, the sacrum consisted of five co-ossified sacral vertebrae. As in Giraffatitan, the sacrum was proportionally broad and featured very short neural spines. Poor preservation of the sacral material in Giraffatitan however precludes detailed comparisons between both genera. Of the tail, only the second caudal vertebra is well preserved. As in Giraffatitan, this vertebra was slightly amphicoelous (concave on both ends), lacked openings on the sides, and possessed a short neural spine that was rectangular and tilted backwards. In contrast to the second caudal vertebra of Giraffatitan, that of Brachiosaurus showed a proportionally taller neural arch, making the vertebra ca. 30% taller. The centrum showed no depressions at its sides, in contrast to Giraffatitan. In front or back view, the neural spine broadened towards its tip to approximately three times its minimum width. In Giraffatitan, in contrast, no widening is apparent. The neural spines were also inclined backwards by about 30°, more than in Giraffatitan (20°). The caudal ribs projected laterally and were not tilted backwards as in Giraffatitan. The articular facets of the articular processes at the back of the vertebra were directed more downwards, while those of Giraffatitan faced more towards the sides. Besides the articular processes, the hyposphene-hypantrum articulation formed an additional articulation between vertebrae, making the vertebral column more rigid; in Brachiosaurus, the hyposphene was much more pronounced than in Giraffatitan.
The coracoid was semicircular and taller than broad. Differences from Giraffatitan are related to its shape in side view, including the straighter suture between the coracoid and the scapula. Moreover, the articular surface forming the shoulder joint was thicker and directed more sidewards than in Giraffatitan and other sauropods, possibly indicating a more sprawled forelimb. The humerus, as preserved, measures 204 centimeters (80 in) in total length, although part of its lower end are lost to erosion; its original length is estimated to have been 216 centimeters (85 in). This bone was more slender in Brachiosaurus than in most other sauropods, measuring only 28.5 centimeters (11.2 in) in width at its narrowest part. It was, however, more robust than that of Giraffatitan, being around 10% broader at both the upper and lower ends. At its upper end, it featured a low bulge visible in side view, which is absent in Giraffatitan. Distinguishing features can also be found in the ilium of the pelvis. In Brachiosaurus, the ischiadic peduncle, a downwards projecting extension connecting to the ischium, reaches farther downwards than in Giraffatitan. While the latter genus shows a sharp notch between the ischiadic peduncle and the back portion of the ilium, this notch is more rounded in Brachiosaurus. On the upper surface of the hind part of the bone, Brachiosaurus showed a pronounced tubercle that is absent in other sauropods. Of the hind limb, the femur was very similar to that of Giraffatitan. As in the latter genus, it was strongly elliptical in cross-section, being more than twice as wide in front or back view than in side view. The femur of Brachiosaurus, however, was slightly more robust than that of Giraffatitan. Further differences include the more prominent and further downwards located fourth trochanter, a bulge on the femur serving as the anchor point for the most important locomotory muscle, the caudofemoralis. Furthermore, the condyles at the lower end were not extending backwards as strongly as in Giraffatitan; both condyles were similar in width in Brachiosaurus but unequal in Giraffatitan.
Though no skull remains were discovered with the original Brachiosaurus skeleton, one partial skull from 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 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. 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 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).
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. 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 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 that was open until below the ninth alveolus, continuing thereafter as a shallow through.
Each maxilla had space for about 14 or 15 teeth, whereas Giraffatitan had 11 and Camarasaurus 8 to 10. The maxillae contained replacement teeth which showed rugose enamel, similar to Camarasaurus, but lacked the small denticles (serrations) along the edges. Since the maxilla was wider than that of Camarasaurus, Brachiosaurus would have possessed 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 ended well in front of the antorbital fenestra (the opening in front of the orbit), whereas they ended just before and below the fenestra in Camarasaurus and Shunosaurus.
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 at 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 to have used their large nasal openings as snorkels when submerged.
History of discovery
The Brachiosaurus holotype
The genus Brachiosaurus, and its type species B. altithorax, are based on a partial postcranial skeleton from Fruita, in the valley of the Colorado River of western Colorado. This specimen was collected from rocks of the Brushy Basin Member of the Morrison Formation 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. It is currently cataloged as FMNH P 25107.
Riggs and company were working in the area as a result of favorable correspondence between Riggs and Stanton Merill Bradbury, a dentist in nearby Grand Junction. In the spring of 1899, Riggs had sent letters to mayors in western Colorado, inquiring after possible trails leading from railway heads into northeastern Utah, where he hoped to find fossils of Eocene mammals. To his surprise, he was informed by Bradbury, an amateur collector himself and president of the Western Colorado Academy of Science, that dinosaur bones had been collected near Grand Junction since 1885. Riggs was sceptical of this claim, but his superior, curator of geology Oliver Cummings Farrington, was very eager to add a large sauropod skeleton to the collection, to outdo other institutions, and convinced the museum management to invest five hundred dollars in an expedition. Arriving on 20 June, they set camp at the abandoned Goat Ranch. During a prospect on horse-back, Riggs' field assistant Harold William Menke found the humerus of FMNH P 25107, on July 4, 1900, exclaiming it was "the biggest thing yet!". Riggs at first took the find for a badly preserved Brontosaurus specimen and gave priority to excavating Quarry 12, which held a more promising Morosaurus skeleton. Having secured that, on 26 July he returned to the humerus in Quarry 13, which soon proved to be of enormous size, convincing a puzzled Riggs that he had discovered the largest land animal ever. The site, 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. During excavation of the specimen, Riggs misidentified the humerus as a deformed femur due to its great length, and found himself confirmed when an equally sized, well-preserved femur of the same skeleton was discovered. In 1904, Riggs noted: "Had it not been for the unusual size of the ribs found associated with it, the specimen would have been discarded as an Apatosaur, too poorly preserved to be of value." It was only after preparation of the fossil material in the laboratory that the bone was recognized as a humerus. The excavation attracted large numbers of visitors, delaying the work and forcing Menke to guard the site to prevent bones from being looted. On 17 August, the last bone was jacketed in plaster. After a concluding ten-day prospecting trip, the expedition returned to Grand Junction and hired a team and wagon to transport all fossils to the railway station, during five days; another week was spent to pack them in thirty-eight crates with a weight of 12,500 pounds (5,700 kg). On 10 September, Riggs left for Chicago by train, arriving on the 15th; the railroad companies let both passengers and cargo travel for free, as a public relations gesture.
The holotype skeleton 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. Riggs described the coracoid as from the left side of the body, but restudy has shown it to be a right coracoid. At the time of discovery, the lower end of the humerus, the underside of the sacrum, the ilium and the preserved caudal vertebrae were exposed to the air and thus partly damaged by weathering. The vertebrae were only slightly shifted out of their original anatomical position; they were found with their top sides directed downwards. The ribs, humerus, and coracoid, however, were displaced to the left side of the vertebral column, indicating transportation by a water current. This is further evidenced by an isolated ilium of Diplodocus that apparently had drifted against the vertebral column, as well as by a change in composition of the surrounding rocks. While the specimen itself was imbedded in fine-grained clay, indicating low-energy conditions at the time of deposition, it was cut off at the seventh vertebra by a thick layer of much coarser sediments consisting of pebbles at its base and sandstone further up, indicating deposition under stronger currents. Based on this evidence, Riggs in 1904 suggested that the missing front part of the skeleton was washed away by a water current, while the hind part was already covered by sediment and thus got preserved.
Riggs published a short report of the new find 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. The titles of Riggs' 1901 and 1903 articles suggested that the specimen was the "largest known dinosaur". Riggs derived the genus name from the Greek brachion/βραχίων meaning "arm" and sauros/σαυρος meaning "lizard", because he realized that the length of the arms was unusual for a sauropod. 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". Riggs followed his 1903 publication that named Brachiosaurus altithorax with a more detailed description in a monograph in 1904.
Preparation of the holotype began in the fall of 1900 shortly after it was collected by Riggs for the Field Museum. 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, solitarily, still on display by 1908 in Hall 35 when the Field Museum's newly mounted Apatosaurus was unveiled, the very specimen Riggs had found in Quarry 12, today catalogued as FMNH P25112 and identified as a Brontosaurus exemplar. However, no mount of Brachiosaurus 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 Tyrannosaurus skeleton, "Sue". 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 humeri and two dorsals in the Mesozoic Hall of the Field Museum's Evolving Planet exhibit.
In 1969, in a study by R.F. Kingham, Brachiosaurus altithorax, "B." brancai and "B." atalaiensis, along with many species now assigned to other genera, were placed in the genus Astrodon, creating an Astrodon altithorax. Kingham's views of brachiosaurid taxonomy have, however, not been accepted by many other authors.
In 1883, farmer Marshall Parker Felch, a fossil collector for the American paleontologist Othniel Charles Marsh, reported the discovery of a sauropod skull in Felch Quarry 1, near Garden Park, Colorado. The skull was found in yellowish white sandstone, near a 1 meter (3.3 ft) long cervical vertebra, which was destroyed during an attempt to collect it. The skull was catalogued as YPM 1986, and sent to Marsh at the Peabody Museum of Natural History, who incorporated it into his 1891 skeletal restoration of Brontosaurus (perhaps because Felch had identified it as belonging to that dinosaur). The Felch Quarry skull consists of the cranium, the maxillae, the right postorbital, part of the left maxilla, the left squamosal, the right quadrate, the dentaries, a possible partial pterygoid, and a front tooth from the dentary. The bones were roughly prepared for Marsh, which lead to some damage. Most of the specimens collected by Felch were sent to the National Museum of Natural History in 1899 after Marsh's death, including the skull, which was then catalogued as USNM 5730.
In 1975, the American paleontologists Jack McIntosh and David Berman investigated the historical issue of whether Marsh had assigned an incorrect skull to Brontosaurus (at the time thought to be a junior synonym of Apatosaurus), and found the Felch Quarry skull to be of "the general Camarasaurus type", while suggesting that the vertebra found near it belonged to Brachiosaurus. They concluded that if Marsh had not arbitrarily assigned the Felch quarry skull and another Camarasaurus-like skull to Brontosaurus, it would have been recognized earlier that the actual skull of Brontosaurus and Apatosaurus was more similar to that of Diplodocus. McIntosh later tentatively recognized the Felch Quarry skull as belonging to Brachiosaurus, and brought it to the attention of the American paleontologists Kenneth Carpenter and Virginia Tidwell, while urging them to descibe it. They brought the skull to the Denver Museum of Natural History, where they further prepared it and made a reconstruction of it based on casts of the individual bones, with the skulls of Giraffatitan and Camarasaurus acting as templates for the missing bones. In 1998, Carpenter and Tidwell described the Felch Quarry skull, and formally assigned it to B. sp., since it is impossible to determine whether it belonged to the species B. altithorax itself.
Additional discoveries of Brachiosaurus material in North America have been uncommon and consist of a handful of bones. Material has been described from Colorado, Oklahoma, Utah, and Wyoming, and undescribed material has been mentioned from several other sites. 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, the latter renamed Ultrasauros shortly thereafter because another sauropod already received the name. 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, specimen BYU 9462 (previously BYU 5001), is now assigned to Brachiosaurus, but the species is uncertain. 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.
Taylor listed a number of specimens referred to Brachiosaurus in 2009. 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. In contrast, a cervical vertebra and the skull mentioned above may belong to either B. altithorax or an as-yet unknown brachiosaurid from North America. The cervical was found near Jensen, Utah, by Jensen, and – if it belongs to Brachiosaurus – is one of a handful of neck vertebrae known for American brachiosaurids. There is no unambiguous material of the skull, neck, anterior dorsal region, distal (lower) limbs or feet. In 2012, José Carballido and colleagues 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, SMA 0009 nicknamed "Toni", was originally thought to belong to a diplodocid, but the authors reinterpreted it as representing a brachiosaurid, probably Brachiosaurus altithorax. In 2018, the largest sauropod foot ever found was reported from the Morrison Formation in Wyoming, and though possibly belonging to Brachiosaurus (the femur of the specimen would have been about 2% larger than that of the B. altithorax holotype), the authors cautiously assigned it to Brachiosauridae indet.
Formerly assigned species
B. brancai and B. fraasi
Between 1909 and 1912, large-scale paleontological expeditions in German East Africa unearthed a considerable amount of brachiosaurid material from the Tendaguru Formation. In 1914, German paleontologist Werner Janensch listed a number of differences and commonalities between these fossils and B. altithorax, concluding they could be referred to the genus Brachiosaurus. From this material Janensch named two species: Brachiosaurus brancai for the larger and more complete taxon, and Brachiosaurus fraasi for the smaller and more poorly known species. In three further publications in 1929, 1950 and 1961 Janensch compared the species in more detail, listing thirteen putative shared characters between Brachiosaurus brancai (which he now considered to include B. fraasi) and Brachiosaurus altithorax. Of these, however, only four appear to be valid, while six pertain to more inclusive groups than the Brachiosauridae, and the rest are either difficult to assess or refer to material that is not Brachiosaurus.
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 institutions 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. Much or all of this material probably belongs to Giraffatitan, although some may represent a new brachiosaurid.
Janensch based his description of B. brancai on "Skelett S" (skeleton S) from Tendaguru, but later realized that it comprised two partial individuals: S I and S II. He at first did not designate them as a syntype series, but in 1935 made S I (presently 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. It includes, among other bones, several dorsal 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 in 2011 Taylor realized that Janensch had designated the smaller skeleton S I as the lectotype in 1935.
In 1988, 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 was a difference in the way the trunk vertebrae vary: they are fairly uniform in length in the African material, but differ widely in B. altithorax. 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 as Brachiosaurus (Giraffatitan) brancai. Giraffatitan was raised to genus level by George Olshevsky in 1991, while referring to the vertebral variation.
A detailed 2009 study by Taylor of all material, including the limb and girdle bones, found that there are significant differences between B. altithorax and the Tendaguru material in all elements known from both species. Taylor found twenty-six distinct osteological (bone-based) characters, a larger difference than that between e.g. Diplodocus and Barosaurus, and therefore argued that the African material should indeed be placed in its own genus—Giraffatitan—as Giraffatitan brancai. An important difference between the two genera is the overall body shape, with Brachiosaurus having a 23% longer dorsal vertebrate series and a 20 to 25% longer and also taller tail.
Originally described by Albert-Félix de Lapparent and Georges Zbyszewski in 1957, "B." atalaiensis referral to Brachiosaurus was doubted in 2004 by Paul Upchurch, Barret and Dodson, who listed it as an unnamed brachiosaurid genus; it was placed it in its own genus Lusotitan by Miguel Telles Antunes and Octávio Mateus in 2003. 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.
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. 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), but more recent review assigns it to the "Continental intercalaire," which is considered to be of Albian age (late Early Cretaceous, significantly younger).
"B." nougaredi was formerly considered to be a species of Brachiosaurus, or a distinct, unnamed brachiosaurid, but a 2013 analysis by Philip D. Mannion and colleagues found that the remains probably belong to more than one species. 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.
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. 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. When describing Brachiosaurus brancai and B. fraasi, Janensch noted the slenderness of the humerus was unique to all three Brachiosaurus species and Pelorosaurus. Cetiosaurus was also mentioned to have a more slender humerus, but not as much as in Brachiosaurus or Pelorosaurus. Over the years, a number of sauropods have been assigned to Brachiosauridae, such as Astrodon, Bothriospondylus, Dinodocus, Pelorosaurus, Pleurocoelus, and Ultrasaurus, but most of these are currently regarded as dubious or of uncertain placement. A phylogenetic analysis of sauropods published in 2010 found that Abydosaurus formed a clade with Brachiosaurus and Giraffatitan (included in Brachiosaurus). Another 2010 analysis focused on possible Asian brachiosaurid material found a clade including Abydosaurus, Brachiosaurus, Cedarosaurus, Giraffatitan, and Paluxysaurus, but not Qiaowanlong, the putative Asian brachiosaurid. Related genera include Lusotitan and Sauroposeidon. Brachiosauridae is situated at the base of Titanosauriformes, a group of sauropods that also includes the titanosaurs.
According to the revised 2009 diagnosis by Taylor, Brachiosaurus altithorax can be distinguished by a plethora of characters, many to be found on the dorsal vertebrae. 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). The cladogram of Brachiosauridae below follows that published by Michael D. D'Emic in 2012.
It was believed throughout the 19th and early 20th centuries that sauropods like Brachiosaurus were too massive to support their own weight on dry land. It was theorized that they lived partly submerged in water. Riggs however, concluded that Brachiosaurus was a fully terrestrial animal and more recent findings have supported this. It is estimated that sauropods could not have breathed through their nostrils when the rest of the body was submerged, as the water pressure on the chest wall would be too great. In addition, the hollowness of the bones would have made the sauropods buoyant.
Like all sauropods, Brachiosaurus was probably 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. In the past, Brachiosaurus has been used as 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. 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. The large nasal arch has been postulated as an adaptation for cooling the brain, as a surface for evaporative cooling of the blood.
It has been proposed that sauropods, including Brachiosaurus, may have had proboscises based on the position of the bony narial orifice. Fabien Knoll and colleagues disputed this for Diplodocus and Camarasaurus in 2006, finding that the infraorbital foramen (reconstructed from an endocranial cast) was too small. However, they also noted that the facial nerve for Giraffatitan was larger.
Neck posture and movement
Historically, reconstructions of the neck positions of Brachiosaurus have varied from fairly low to nearly vertical. More recent studies have favored an upward posture. Unlike other sauropods like Diplodocus and Apatosaurus, which likely held their heads horizontally, Brachiosaurus and its kin had front limbs which were longer than the hind limbs; elevating the shoulder above the level of the pelvis and giving them a vertebral column that slopes upward. 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 more vertically with its center of mass located above the base of the neck. The angle between the horizontal plane and the middle part of the neck was estimated to have been 60–70 degrees. In addition, the neck likely formed an S-shape most of the time. Brachiosaurids could have adopted a more horizontal posture but only for short periods of time.
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). 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. In addition, the head and neck may have been lowered during locomotion. The flexibility of the neck of sauropods has been debated. Mobility was reconstructed as quite low by Stevens and Parrish. while other researchers like Paul and Christian and Dzemski argued for more flexible necks. In studying the inner ear of Giraffatitan, Gunga & Kirsch (2001) concluded that brachiosaurids would have moved their necks in lateral directions more often than in dorsal-ventral directions.
Feeding and diet
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. 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. 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. 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, so Brachiosaurus may have required only about 120 kilograms (260 lb) of fodder a day. Brachiosaurid 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. As the teeth were not spoon-shaped as with earlier sauropods but of the compressed cone-chisel type, a precision-shear bite was employed. Such teeth are optimized for non-selective nipping. The relatively broad jaws could crop large amounts of plant material. Even if a Brachiosaurus of forty tonnes would have needed half a tonne of fodder, its dietary needs could have been met by a normal cropping action of the head. If it ate during sixteen hours per day, biting off between a tenth and two-thirds of a kilogramme, taking between one and six bites per minute, its daily food intake would have roughly equalled 1.5% of its body mass, similar to the requirement of a modern warm-blooded elephant.
As Brachiosaurus shared its habitat, the Morrison, with many other sauropod species, its specialization of eating tall vegetation, would have been part of a system of niche partitioning, the various taxa thus avoiding competition with each other. A typical food tree might have resembled Sequoiadendron. The fact that such tall conifers were relatively rare in the Morrison might explain why Brachiosaurus was much less common in its ecosystem than the related Giraffatitan, which seems to have been one of the most abundant sauropods in the Tendaguru. Brachiosaurus, with its shorter arm and lower shoulder, was not as well-adapted to high-browsing as Giraffatitan.
It has been suggested that Brachiosaurus could rear into a bipedal or tripodal (with tail support) pose to feed. However, a detailed physical modelling-based analysis of sauropod rearing capabilities by Heinrich Mallison showed that while many sauropods could rear, the unusual body shape and limb length ratio of brachiosaurids 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. A bipedal stance might have been adopted by Brachiosaurus in exceptional situations, like male dominance fights.
The downward mobility of the neck of Brachiosaurus would have allowed it to reach open water at the level of its feet, while standing upright. Modern giraffes spread their forelimbs to lower the mouth in a relatively horizontal position, in order to more easily gulp down the water. It is unlikely that Brachiosaurus could have attained a stable posture this way, forcing the animal to plunge the snout almost vertically into the surface of a lake or stream. This would have submerged its fleshy nostrils if they were located at the tip of the snout and it is possible that they were in fact placed at the top of the head, above the bony nostrils that might have evolved their retracted position for precisely this reason.
The ontogeny of Brachiosaurus has been reconstructed by Carballido and colleagues in 2012 based on SMA 0009, a postcranial skeleton. This specimen represents a quite young juvenile with an estimated total body length of just 2 meters (6.6 ft). It shares some unique traits with the B. altithorax holotype, indicating it is referable to this species. These include an elevation on the rear blade of the ilium; the lack of a postspinal lamina; vertical neural spines on the back; an ilium with a subtle notch between the appendage for the ischium and the rear blade; and the lack of a side bulge on the upper thighbone. However, there are also differences. These might indicate that the juvenile is not a B. altithorax individual after all, but belongs to a new species. Alternatively, they might be explained as juvenile traits that would have changed when the animal matured.
Such changes are especially to be expected in the proportions of an organism. The middle neck vertebrae of SMA 0009 are remarkably short for a sauropod, being just 1.8 times longer than high, compared with a ratio of 4.5 in Giraffatitan. This suggests that the necks of brachiosaurids became proportionally much longer while their backs, to the contrary, experienced relative negative growth. The humerus of SMA 0009 is relatively robust: more slender than that of most basal titanosauriforms but thicker than the upper arm bone of B. altithorax. This suggests that it was already lengthening in an early juvenile stage and became even more slender during growth. This is in contrast to diplodocoids and basal macronarians, whose slender humeri are not due to such allometric growth. Brachiosaurus also appears to have experienced an elongation of the metacarpals, which in juveniles were shorter compared to the length of the radius. SMA 0009 shows a ratio of just 0.33, the lowest known in the entire Neosauropoda.
Another plausible ontogenetic development is the increased pneumatization of the vertebrae. During growth, the diverticula of the air sacs invaded the bones and hollowed them out. SMA 0009 already has pleurocoels, pneumatic excavations, at the sides of its neck vertebrae. These are divided by a ridge but are otherwise still very simple in structure, compared with the extremely complex ridge systems typically shown by adult derived sauropods. Its back vertebrae still completely lack such pleurocoels.
Two traits are not so obviously linked to ontogeny. The neural spines of the rear back vertebrae and the front sacral vertebrae are extremely transversely compressed, being eight times longer from front to rear than wide from side to side. The spinodiapophyseal lamina or "SPOL", the ridge normally running from each side of the neural spine towards each diapophysis, the transverse process bearing the contact facet for the upper rib head, is totally lacking. Both traits could be autapomorphies, unique derived characters proving that SMA 0009 represents a distinct species. However, there are indications that these traits are growth-related as well. Of the basal sauropod Tazoudasaurus a young juvenile is known that also lacks the spinodiapophyseal lamina, whereas the adult form has an incipient ridge. A very young juvenile of Europasaurus shows a weak SPOL but it is well developed in mature individuals. These two cases represent the only finds in which the condition can be checked; they suggest that the SPOL developed during growth. As this very ridge widens the neural spine, its transverse compression is not an independent trait and the development of the SPOL plausibly precedes the thickening of the neural spine with more mature animals.
Sauropods were likely able to sexually reproduce before they attained their maximum individual size. The maturation rate differed between species. Its bone structure indicates that Brachiosaurus was able to reproduce when it reached 40% of its maximal size.
Brachiosaurus is known only from the Morrison Formation of western North America (following the reassignment of the African species). The Morrison Formation is interpreted as a semiarid environment with distinct wet and dry seasons, and flat floodplains. Several other sauropod genera were present in the Morrison Formation, with differing body proportions and feeding adaptations. Among these were Apatosaurus, Barosaurus, Camarasaurus, Diplodocus, Haplocanthosaurus, and Supersaurus. Brachiosaurus was one of the less abundant Morrison Formation sauropods. In a 2003 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). 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, unlike many other types of sauropod which have been found throughout the formation. If the large foot reported from Wyoming (the nothernmost occurrence of a brachiosaurid in North America) did belong to Brachiosaurus, the genus would have covered a wide range of latitudes. Brachiosaurids could process tough vegetation with their broad-crowned teeth, and might therefore have covered a wider range of vegetational zones than for example diplodocids. Camarasaurids, which have a similar tooth morphology to brachiosaurids, were also widespread and are known to have migrated seasonally, so this might have also been true for brachiosaurids as well.
Other dinosaurs known from the Morrison Formation include the predatory theropods Koparion, Stokesosaurus, Ornitholestes, Ceratosaurus, Allosaurus and Torvosaurus, the herbivorous ornithischians Camptosaurus, Dryosaurus, Othnielia, Gargoyleosaurus and Stegosaurus. Allosaurus accounted for 70 to 75% of theropod specimens and was at the top trophic level of the Morrison food web. Ceratosaurus might have specialized in attacking large sauropods, including smaller individuals of Brachiosaurus. 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 in otherwise treeless settings (gallery forests) with tree ferns, and ferns, to fern savannas with occasional trees such as the Araucaria-like conifer Brachyphyllum.
Brachiosaurus has been called one of the most iconic dinosaurs, but most popular depictions are based on the African species B. brancai which has since been moved to its own genus, Giraffatitan. A main belt asteroid, 1991 GX7, was named 9954 Brachiosaurus in honor of the genus in 1991. Brachiosaurus was featured in the 1993 movie Jurassic Park, as the first computer generated dinosaur shown. These effects were considered ground-breaking at the time, and the awe of the movie's characters upon seeing the dinosaur for the first time was mirrored by audiences. The movements of the movie's Brachiosaurus were based on the gait of a giraffe combined with the mass of an elephant. A scene later in the movie used an animatronic head and neck, for when a Brachiosaurus interacts with human characters. The digital model of Brachiosaurus used in Jurassic Park later became the starting point for the ronto models in the 1997 special edition of the film Star Wars Episode IV: A New Hope.
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