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I know that Diplodocus is marked by the feature of having a double row of or "double-beamed" chevron bones in the tail, but how diagnostic is this feature if several other sauropods have it? I mean, if there are other genera with the feature, which ones are they, so I know not to confuse them with Diplodocus?
It's fairly common. It is believed to have evolved two times independently, basically in both groups presumed to use their tails as weapons. Both Diplodocoidea and Euhelopodidae have species with forked chevrons and evolved it independently. It is fairly diagnostic since it is not seen outside these groups.
Independent half chevrons (two rows of individual elongated splints of bone, one right, one left) pop up in many groups but double beamed chevrons are something different: the ends of the chevrons are joined, creating a single solid structure. In some parts of the tail they are separated into right and left halves (these are not very unique), but the joined ones are taxonomically significant. These are not chevrons dwindling into nothing along the tail but changing structure in a specific structurally significant way.
Opisthocoelicaudia / ɒ ˌ p ɪ s θ oʊ s ɪ l ɪ ˈ k ɔː d i ə / is a genus of sauropod dinosaur of the Late Cretaceous Period discovered in the Gobi Desert of Mongolia. The type species is Opisthocoelicaudia skarzynskii. A well-preserved skeleton lacking only the head and neck was unearthed in 1965 by Polish and Mongolian scientists, making Opisthocoelicaudia one of the best known sauropods from the Late Cretaceous. Tooth marks on this skeleton indicate that large carnivorous dinosaurs had fed on the carcass and possibly had carried away the now-missing parts. To date, only two additional, much less complete specimens are known, including part of a shoulder and a fragmentary tail. A relatively small sauropod, Opisthocoelicaudia measured about 11.4–13 m (37–43 ft) in length. Like other sauropods, it would have been characterised by a small head sitting on a very long neck and a barrel shaped trunk carried by four column-like legs. The name Opisthocoelicaudia means "posterior cavity tail", alluding to the unusual, opisthocoel condition of the anterior tail vertebrae that were concave on their posterior sides. This and other skeletal features lead researchers to propose that Opisthocoelicaudia was able to rear on its hindlegs.
Named and described by Polish paleontologist Maria Magdalena Borsuk-Białynicka in 1977, Opisthocoelicaudia was first thought to be a new member of the Camarasauridae, but is currently considered a derived member of the Titanosauria. Its exact relationships within Titanosauria are contentious, but it may have been close to the North American Alamosaurus. All Opisthocoelicaudia fossils stem from the Nemegt Formation. Despite being rich in dinosaur fossils, the only other sauropod from this rock unit is Nemegtosaurus, which is known from a single skull. Since the skull of Opisthocoelicaudia remains unknown, several researchers have suggested that Nemegtosaurus and Opisthocoelicaudia may represent the same species. Sauropod footprints from the Nemegt Formation, which include skin impressions, can probably be referred to either Nemegtosaurus or Opisthocoelicaudia as these are the only known sauropods from this formation.
One of the best-known sauropods, Diplodocus was a large long-necked four-legged animal, with a long, whip-like tail. Its front limbs were a bit shorter than its hind limbs, which forms a horizontal stance for the most part. The long-necked, long-tailed animal with four sturdy legs has been mechanically compared with a suspension bridge. In fact, Diplodocus is the longest dinosaur known from a complete skeleton. ΐ] Diplodocus species ranged from 80–115 ft (26-35 m) and weighed 10-16 metric tons. Α] Β] Γ] Δ]
The skull of Diplodocus was very small, compared with the size of the animal, which could reach up to 115 ft, Ε] of which over 20 ft was neck. Ζ] Diplodocus had small, 'peg'-like teeth that pointed forward and were only found in the front of the jaws. Η] The neck was formed by at least 15 vertebrae and is now believed to have been held parallel to the ground most of the time and unable to have been raised much past horizontal. ⎖]
Diplodocus had an 8 m long neck and a short 6 ft head. Its 14 m long tail had 80 vertebrae, ⎗] and might have been used like a whip either to attack predators ⎘] or to make whip-cracking noises. ⎙] The tail may have served as a counterbalance for the neck. The tail vertebrae had double beams (hence the name Diplodocus: double beam) that may have protected the blood vessels from being crushed if the tail pressed against the ground.
Like most sauropods, the front "feet" of Diplodocus were highly modified, with the finger and hand bones arranged upright, horseshoe-shaped in cross section. Diplodocus lacked claws on all but one toe of the front limb, and this claw was strangely large compared to other sauropods, flat from side to side, and detached from the bones of the hand. The role of this odd skilled claw is not known. ⎚]
Among the best-known sauropods, Diplodocus were very large, long-necked, quadrupedal animals, with long, whip-like tails. Their forelimbs were slightly shorter than their hind limbs, resulting in a largely horizontal posture. The skeletal structure of these long-necked, long-tailed animals supported by four sturdy legs have been compared with suspension bridges.  In fact, Diplodocus carnegii is currently one of the longest dinosaurs known from a complete skeleton,  with a total length of 24 meters (79 ft).  Modern mass estimates for Diplodocus carnegii have tended to be in the 11–14.8-metric-ton (12.1–16.3-short-ton) range.   
Diplodocus hallorum, known from partial remains, was even larger, and is estimated to have been the size of four elephants.  When first described in 1991, discoverer David Gillette calculated it may have been up to 52 m (171 ft) long,  making it the longest known dinosaur (excluding those known from exceedingly poor remains, such as Amphicoelias). Some weight estimates of this time ranged as high as 113 metric tons (125 short tons). The estimated length was later revised downward to 33–33.5 m (108–110 ft) and later on to 32 m (105 ft)     based on findings that show that Gillette had originally misplaced vertebrae 12–19 as vertebrae 20–27. The nearly complete Diplodocus carnegii skeleton at the Carnegie Museum of Natural History in Pittsburgh, Pennsylvania, on which size estimates of D. hallorum are mainly based, also was found to have had its 13th tail vertebra come from another dinosaur, throwing off size estimates for D. hallorum even further. While dinosaurs such as Supersaurus were probably longer, fossil remains of these animals are only fragmentary. 
Diplodocus had an extremely long tail, composed of about 80 caudal vertebrae,  which are almost double the number some of the earlier sauropods had in their tails (such as Shunosaurus with 43), and far more than contemporaneous macronarians had (such as Camarasaurus with 53). Some speculation exists as to whether it may have had a defensive  or noisemaking (by cracking it like a coachwhip) function.  The tail may have served as a counterbalance for the neck. The middle part of the tail had "double beams" (oddly shaped chevron bones on the underside, which gave Diplodocus its name). They may have provided support for the vertebrae, or perhaps prevented the blood vessels from being crushed if the animal's heavy tail pressed against the ground. These "double beams" are also seen in some related dinosaurs. Chevron bones of this particular form were initially believed to be unique to Diplodocus since then they have been discovered in other members of the diplodocid family as well as in non-diplodocid sauropods, such as Mamenchisaurus. 
Like other sauropods, the manus (front "feet") of Diplodocus were highly modified, with the finger and hand bones arranged into a vertical column, horseshoe-shaped in cross section. Diplodocus lacked claws on all but one digit of the front limb, and this claw was unusually large relative to other sauropods, flattened from side to side, and detached from the bones of the hand. The function of this unusually specialized claw is unknown. 
No skull has ever been found that can be confidently said to belong to Diplodocus, though skulls of other diplodocids closely related to Diplodocus (such as Galeamopus) are well known. The skulls of diplodocids were very small compared with the size of these animals. Diplodocus had small, 'peg'-like teeth that pointed forward and were only present in the anterior sections of the jaws.  Its braincase was small. The neck was composed of at least 15 vertebrae and may have been held parallel to the ground and unable to be elevated much past horizontal. 
The discovery of partial diplodocid skin impressions in 1990 showed that some species had narrow, pointed keratinous spines, much like those on an iguana and up to 18 centimeters (7.1 in) long, on the "whiplash" portion of their tails, and possibly along the back and neck as well, as in hadrosaurids.   The spines have been incorporated into many recent reconstructions of Diplodocus, notably Walking with Dinosaurs.  The original description of the spines noted that the specimens in the Howe Quarry near Shell, Wyoming were associated with skeletal remains of an undescribed diplodocid "resembling Diplodocus and Barosaurus."  Specimens from this quarry have since been referred to Kaatedocus siberi and Barosaurus sp., rather than Diplodocus.  
Fossilized skin of Diplodocus sp., discovered at the Mother's Day Quarry, exhibits several different types of scale shapes including rectangular, polygonal, pebble, ovoid, dome, and globular. These scales range in size and shape depending upon their location on the integument, the smallest of which reach about 1mm while the largest 10 mm. Some of these scales show orientations that may indicate where they belonged on the body. For instance, the ovoid scales are oriented closely clustered together and look similar to scales in modern reptiles that are located dorsally. Another orientation on the fossil consists of arching rows of square scales that interrupts nearby polygonal scale patterning. It is noted that these arching scale rows look similar to the scale orientations seen around crocodilian limbs, suggesting that this area may have also originated from around a limb on the Diplodocus. The skin fossil itself is small in size, reaching less than 70 cm in length. Due to the vast amount of scale diversity seen within such a small area, as well as the scales being smaller in comparison to other diplodocid scale fossils, and the presence of small and potentially “juvenile” material at the Mother’s Day Quarry, it is hypothesized that the skin originated from a small or even “juvenile” Diplodocus. 
Several species of Diplodocus were described between 1878 and 1924. The first skeleton was found at Cañon City, Colorado, by Benjamin Mudge and Samuel Wendell Williston in 1877, and was named Diplodocus longus ('long double-beam') by paleontologist Othniel Charles Marsh in 1878.  Although not the type species, D. carnegii is the most completely known and most famous species due to the large number of casts of its skeleton in museums around the world.  Diplodocus remains have since been found in the Morrison Formation of the western U.S. states of Colorado, Utah, Montana, and Wyoming. Fossils of this animal are common, except for the skull, which has never been found with otherwise complete skeletons. D. hayi, known from a partial skeleton and skull discovered by William H. Utterback in 1902 near Sheridan, Wyoming, was described in 1924.  In 2015, it was renamed as the separate genus Galeamopus, and several other Diplodocus specimens were referred to that genus, leaving no definite Diplodocus skulls known. 
The two Morrison Formation sauropod genera Diplodocus and Barosaurus had very similar limb bones. In the past, many isolated limb bones were automatically attributed to Diplodocus, but may, in fact, have belonged to Barosaurus.  Fossil remains of Diplodocus have been recovered from stratigraphic zone 5 of the Morrison Formation. 
Valid species Edit
- D. carnegii (also spelled D. carnegiei), named after Andrew Carnegie, is the best known, mainly due to a near-complete skeleton known as Dippy (specimen CM 84) collected by Jacob Wortman, of the Carnegie Museum of Natural History in Pittsburgh, Pennsylvania and described and named by John Bell Hatcher in 1901.  This was reconsidered as type-species for Diplodocus. 
- D. hallorum, first described in 1991 by Gillette as Seismosaurus halli from a partial skeleton comprising vertebrae, pelvis and ribs, specimen NMMNH P-3690, was found in 1979.  As the specific name honours two people, Jim and Ruth Hall, George Olshevsky later suggested to emend the name as S. hallorum, using the mandatory genitive plural Gillette then emended the name,  which usage has been followed by others, including Carpenter (2006).  In 2004, a presentation at the annual conference of the Geological Society of America made a case for Seismosaurus being a junior synonym of Diplodocus.  This was followed by a much more detailed publication in 2006, which not only renamed the species Diplodocus hallorum, but also speculated that it could prove to be the same as D. longus.  The position that D. hallorum should be regarded as a specimen of D. longus was also taken by the authors of a redescription of Supersaurus, refuting a previous hypothesis that Seismosaurus and Supersaurus were the same.  A 2015 analysis of diplodocid relationships noted that these opinions are based on the more complete referred specimens of D. longus. The authors of this analysis concluded that those specimens were indeed the same species as D. hallorum, but that D. longus itself was a nomen dubium. 
Nomina dubia (doubtful species) Edit
- D. longus, the type species, is known from two complete and several fragmentary caudal vertebrae from the Morrison Formation (Felch Quarry) of Colorado. Though several more complete specimens have been attributed to D. longus,  detailed analysis has suggested that the original fossil lacks the necessary features to allow comparison with other specimens. For this reason, it has been considered a nomen dubium, which is not an ideal situation for the type species of a well-known genus like Diplodocus. A petition to the International Commission on Zoological Nomenclature was being considered which proposed to make D. carnegii the new type species.  This proposal was rejected by the ICZN and D. longus has been maintained as the type species. 
- D. lacustris ("of the lake") is a nomen dubium, named by Marsh in 1884 based on specimen YPM 1922 found by Arthur Lakes, consisting of the snout and upper jaw of a smaller animal from Morrison, Colorado.  These remains are now believed to have been from an immature animal, rather than from a separate species.  In 2015, it was concluded that the specimen actually belonged to Camarasaurus. 
Diplodocus is both the type genus of, and gives its name to, the Diplodocidae, the family to which it belongs.  Members of this family, while still massive, are of a markedly more slender build than other sauropods, such as the titanosaurs and brachiosaurs. All are characterised by long necks and tails and a horizontal posture, with fore limbs shorter than hind limbs. Diplodocids flourished in the Late Jurassic of North America and possibly Africa. 
A subfamily, the Diplodocinae, was erected to include Diplodocus and its closest relatives, including Barosaurus. More distantly related is the contemporaneous Apatosaurus, which is still considered a diplodocid, although not a diplodocine, as it is a member of the sister subfamily Apatosaurinae.   The Portuguese Dinheirosaurus and the African Tornieria have also been identified as close relatives of Diplodocus by some authors.   The Diplodocoidea comprise the diplodocids, as well as dicraeosaurids, rebbachisaurids, Suuwassea,   Amphicoelias  and possibly Haplocanthosaurus,  and/or the nemegtosaurids.  This clade is the sister group to Macronaria (camarasaurids, brachiosaurids and titanosaurians).  
Cladogram of the Diplodocidae after Tschopp, Mateus, and Benson (2015) below: 
Due to a wealth of skeletal remains, Diplodocus is one of the best-studied dinosaurs. Many aspects of its lifestyle have been subjects of various theories over the years.  Comparisons between the scleral rings of diplodocines and modern birds and reptiles suggest that they may have been cathemeral, active throughout the day at short intervals. 
Marsh and then Hatcher  assumed that the animal was aquatic, because of the position of its nasal openings at the apex of the cranium. Similar aquatic behavior was commonly depicted for other large sauropods, such as Brachiosaurus and Apatosaurus. A 1951 study by Kenneth A. Kermack indicates that sauropods probably 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.  Since the 1970s, general consensus has the sauropods as firmly terrestrial animals, browsing on trees, ferns, and bushes. 
Scientists have debated as to how sauropods were able to breathe with their large body sizes and long necks, which would have increased the amount of dead space. They likely had an avian respiratory system, which is more efficient than a mammalian and reptilian system. Reconstructions of the neck and thorax of Diplodocus show great pneumaticity, which could have played a role in respiration as it does in birds. 
The depiction of Diplodocus posture has changed considerably over the years. For instance, a classic 1910 reconstruction by Oliver P. Hay depicts two Diplodocus with splayed lizard-like limbs on the banks of a river. Hay argued that Diplodocus had a sprawling, lizard-like gait with widely splayed legs,  and was supported by Gustav Tornier. This hypothesis was contested by William Jacob Holland, who demonstrated that a sprawling Diplodocus would have needed a trench through which to pull its belly.  Finds of sauropod footprints in the 1930s eventually put Hay's theory to rest. 
Later, diplodocids were often portrayed with their necks held high up in the air, allowing them to graze from tall trees. Studies looking at the morphology of sauropod necks have concluded that the neutral posture of Diplodocus neck was close to horizontal, rather than vertical, and scientists such as Kent Stevens have used this to argue that sauropods including Diplodocus did not raise their heads much above shoulder level.   A nuchal ligament may have held the neck in this position.  A 2009 study found that all tetrapods appear to hold the base of their necks at the maximum possible vertical extension when in a normal, alert posture, and argued that the same would hold true for sauropods barring any unknown, unique characteristics that set the soft tissue anatomy of their necks apart from other animals. The study found faults with Stevens' assumptions regarding the potential range of motion in sauropod necks, and based on comparing skeletons to living animals the study also argued that soft tissues could have increased flexibility more than the bones alone suggest. For these reasons they argued that Diplodocus would have held its neck at a more elevated angle than previous studies have concluded. 
As with the related genus Barosaurus, the very long neck of Diplodocus is the source of much controversy among scientists. A 1992 Columbia University study of diplodocid neck structure indicated that the longest necks would have required a 1.6-ton heart – a tenth of the animal's body weight. The study proposed that animals like these would have had rudimentary auxiliary "hearts" in their necks, whose only purpose was to pump blood up to the next "heart".  Some argue that the near-horizontal posture of the head and neck would have eliminated the problem of supplying blood to the brain, as it would not be elevated. 
Diet and feeding Edit
Diplodocines have highly unusual teeth compared to other sauropods. The crowns are long and slender, and elliptical in cross-section, while the apex forms a blunt, triangular point.  The most prominent wear facet is on the apex, though unlike all other wear patterns observed within sauropods, diplodocine wear patterns are on the labial (cheek) side of both the upper and lower teeth.  This implies that the feeding mechanism of Diplodocus and other diplodocids was radically different from that of other sauropods. Unilateral branch stripping is the most likely feeding behavior of Diplodocus,    as it explains the unusual wear patterns of the teeth (coming from tooth–food contact). In unilateral branch stripping, one tooth row would have been used to strip foliage from the stem, while the other would act as a guide and stabilizer. With the elongated preorbital (in front of the eyes) region of the skull, longer portions of stems could be stripped in a single action.  Also, the palinal (backwards) motion of the lower jaws could have contributed two significant roles to feeding behavior: (1) an increased gape, and (2) allowed fine adjustments of the relative positions of the tooth rows, creating a smooth stripping action. 
Young et al. (2012) used biomechanical modelling to examine the performance of the diplodocine skull. It was concluded that the proposal that its dentition was used for bark-stripping was not supported by the data, which showed that under that scenario, the skull and teeth would undergo extreme stresses. The hypotheses of branch-stripping and/or precision biting were both shown to be biomechanically plausible feeding behaviors.  Diplodocine teeth were also continually replaced throughout their lives, usually in less than 35 days, as was discovered by Michael D'Emic et al. Within each tooth socket, as many as five replacement teeth were developing to replace the next one. Studies of the teeth also reveal that it preferred different vegetation from the other sauropods of the Morrison, such as Camarasaurus. This may have better allowed the various species of sauropods to exist without competition. 
The flexibility of Diplodocus neck is debated but it should have been able to browse from low levels to about 4 m (13 ft) when on all fours.   However, studies have shown that the center of mass of Diplodocus was very close to the hip socket   this means that Diplodocus could rear up into a bipedal posture with relatively little effort. It also had the advantage of using its large tail as a 'prop' which would allow for a very stable tripodal posture. In a tripodal posture Diplodocus could potentially increase its feeding height up to about 11 m (36 ft).  
The neck's range of movement would have also allowed the head to graze below the level of the body, leading some scientists to speculate on whether Diplodocus grazed on submerged water plants, from riverbanks. This concept of the feeding posture is supported by the relative lengths of front and hind limbs. Furthermore, its peg-like teeth may have been used for eating soft water plants.  Matthew Cobley et al. (2013) dispute this, finding that large muscles and cartilage would have limited neck movements. They state that the feeding ranges for sauropods like Diplodocus were smaller than previously believed and the animals may have had to move their whole bodies around to better access areas where they could browse vegetation. As such, they might have spent more time foraging to meet their minimum energy needs.   The conclusions of Cobley et al. were disputed in 2013 and 2014 by Mike Taylor, who analysed the amount and positioning of intervertebral cartilage to determine the flexibility of the neck of Diplodocus and Apatosaurus. Taylor found that the neck of Diplodocus was very flexible, and that Cobley et al. were incorrect, in that flexibility as implied by bones is less than in reality. 
In 2010, Whitlock et al. described a juvenile skull at the time referred to Diplodocus (CM 11255) that differed greatly from adult skulls of the same genus: its snout was not blunt, and the teeth were not confined to the front of the snout. These differences suggest that adults and juveniles were feeding differently. Such an ecological difference between adults and juveniles had not been previously observed in sauropodomorphs. 
Reproduction and growth Edit
While the long neck has traditionally been interpreted as a feeding adaptation, it was also suggested  that the oversized neck of Diplodocus and its relatives may have been primarily a sexual display, with any other feeding benefits coming second. A 2011 study refuted this idea in detail. 
While no evidence indicates Diplodocus nesting habits, other sauropods, such as the titanosaurian Saltasaurus, have been associated with nesting sites.   The titanosaurian nesting sites indicate that they may have laid their eggs communally over a large area in many shallow pits, each covered with vegetation. Diplodocus may have done the same. The documentary Walking with Dinosaurs portrayed a mother Diplodocus using an ovipositor to lay eggs, but it was pure speculation on the part of the documentary author.  For Diplodocus and other sauropods, the size of clutches and individual eggs were surprisingly small for such large animals. This appears to have been an adaptation to predation pressures, as large eggs would require greater incubation time and thus would be at greater risk. 
Based on a number of bone histology studies, Diplodocus, along with other sauropods, grew at a very fast rate, reaching sexual maturity at just over a decade, and continued to grow throughout their lives.   
The Morrison Formation is a sequence of shallow marine and alluvial sediments which, according to radiometric dating, ranges between 156.3 million years old (Ma) at its base,  and 146.8 million years old at the top,  which places it in the late Oxfordian, Kimmeridgian, and early Tithonian stages of the Late Jurassic period. This formation is interpreted as a semiarid environment with distinct wet and dry seasons. The Morrison Basin, where dinosaurs lived, stretched from New Mexico to Alberta and Saskatchewan, and was formed when the precursors to the Front Range of the Rocky Mountains started pushing up to the west. The deposits from their east-facing drainage basins were carried by streams and rivers and deposited in swampy lowlands, lakes, river channels, and floodplains.  This formation is similar in age to the Lourinha Formation in Portugal and the Tendaguru Formation in Tanzania. 
The Morrison Formation records an environment and time dominated by gigantic sauropod dinosaurs.  Dinosaurs known from the Morrison include the theropods Ceratosaurus, Koparion, Stokesosaurus, Ornitholestes, Allosaurus and Torvosaurus, the sauropods Apatosaurus, Brachiosaurus, Camarasaurus, and Diplodocus, and the ornithischians Camptosaurus, Dryosaurus, Othnielia, Gargoyleosaurus and Stegosaurus.  Diplodocus is commonly found at the same sites as Apatosaurus, Allosaurus, Camarasaurus, and Stegosaurus.  Allosaurus accounted for 70 to 75% of theropod specimens and was at the top trophic level of the Morrison food web.  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).  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. 
Diplodocus has been a famous and much-depicted dinosaur as it has been on display in more places than any other sauropod dinosaur.  Much of this has probably been due to its wealth of skeletal remains and former status as the longest dinosaur.
The donation of many mounted skeletal casts of "Dippy" by industrialist Andrew Carnegie to potentates around the world at the beginning of the 20th century  did much to familiarize it to people worldwide. Casts of Diplodocus skeletons are still displayed in many museums worldwide, including D. carnegii in a number of institutions. 
This project, along with its association with 'big science', philanthropism, and capitalism, drew much public attention in Europe. The German satirical weekly Kladderadatsch devoted a poem to the dinosaur:
|Auch ein viel älterer Herr noch muß |
Den Wanderburschen spielen
Er ist genannt Diplodocus
und zählt zu den Fossilen
Herr Carnegie verpackt ihn froh
In riesengroße Archen
Und schickt als Geschenk ihn so
An mehrere Monarchen 
|But even a much older gent |
Sees itself forced to wander
He goes by the name Diplodocus
And belongs among the fossils
Mr. Carnegie packs him joyfully
Into giant arks
And sends him as gift
To several monarchs
"Le diplodocus" became a generic term for sauropods in French, much as "brontosaur" is in English. 
D. longus is displayed the Senckenberg Museum in Frankfurt (a skeleton made up of several specimens, donated in 1907 by the American Museum of Natural History), Germany.   A mounted and more complete skeleton of D. longus is at the Smithsonian National Museum of Natural History in Washington, DC,  while a mounted skeleton of D. hallorum (formerly Seismosaurus), which may be the same as D. longus, can be found at the New Mexico Museum of Natural History and Science. 
Dance musician Diplo derived his name from the dinosaur. 
A war machine (landship) from WW1 named Boirault machine was designed in 1915, later deemed impractical and hence given a nickname "Diplodocus militaris". 
- ^ Ulrich Merkl (November 25, 2015). Dinomania: The Lost Art of Winsor McCay, The Secret Origins of King Kong, and the Urge to Destroy New York. Fantagraphics Books. ISBN978-1-60699-840-3 . Although it narrowly failed to win the race with the New York Museum of Natural History in 1905, the Diplodocus carnegii is the most famous dinosaur skeleton today, due to the large number of casts in museums around the world
- ^ Breithaupt, Brent H, The discovery and loss of the “colossal” Brontosaurus giganteus from the fossil fields of Wyoming (USA) and the events that led to the discovery of Diplodocus carnegii: the first mounted dinosaur on the Iberian Peninsula, VI Jornadas Internacionales sobre Paleontología de Dinosaurios y su Entorno, September 5–7, 2013, p.49: "“Dippy" was and still is the most widely seen and best-known dinosaur ever found."
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The genus Brachiosaurus is based on a partial postcranial skeleton discovered in 1900 in the valley of the Colorado River near Fruita, Colorado.  This specimen, which was later declared the holotype, comes from rocks of the Brushy Basin Member of the Morrison Formation, and therefore is late Kimmeridgian in age, about 154 to 153 million years old.  Discovered 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 skeptical 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 June 20, 1900 they set camp at the abandoned Goat Ranch.  During a prospecting trip on horseback, Riggs' field assistant Harold William Menke found the humerus of FMNH P 25107,  on July 4,  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 July 26 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, is located on a small hill later known as Riggs Hill it is today marked by a plaque. More 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 this seemed to be confirmed when an equally-sized, well-preserved real 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 August 17, 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 5,700 kilograms (12,500 lb).  On September 10, 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 several 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 downward. 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 embedded in fine-grained clay, indicating low-energy conditions at the time of deposition, it was cut off at the seventh presacral 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.  In 1903, he named the type species Brachiosaurus altithorax.  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 specific epithet was chosen because of the unusually deep and wide chest cavity, from Latin altus "deep" and Greek thorax/θώραξ, "breastplate, cuirass, corslet".  Latin thorax was derived from the Greek and had become a usual scientific designation for the chest of the body. The titles of Riggs' 1901 and 1903 articles emphasized that the specimen was the "largest known dinosaur".   Riggs followed his 1903 publication 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. First the limb elements were processed. In the winter of 1904, the badly weathered vertebrae of the back and hip were prepared by James B. Abbott and C.T. Kline.  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, the Field Museum's first location. 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.  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 material of the related Brachiosaurus brancai (now Giraffatitan) in Museum für Naturkunde, 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) which is on display outside the museum on the NW terrace.  Another outdoor cast was sent to Disney's Animal Kingdom to serve as a gateway icon for the "DinoLand, U.S.A." area, known as the "Oldengate Bridge" that connects the two halves of the fossil quarry themed Boneyard play area. 
Further discoveries of Brachiosaurus material in North America have been uncommon and consist of a few bones. To date, material can only be unambiguously ascribed to the genus when overlapping with the holotype material, and any referrals of elements form the skull, neck, anterior dorsal region, or distal limbs or feet remain tentative. Nevertheless, material has been described from Colorado,     Oklahoma,   Utah,   and Wyoming,   and undescribed material has been mentioned from several other sites.  
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-long (3 ft 3 + 1 ⁄ 2 in) cervical vertebra, which was destroyed during an attempt to collect it. The skull was cataloged 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 dentaries, and a possible partial pterygoid. The bones were roughly prepared for Marsh, which led 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 cataloged 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 describe 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 Brachiosaurus sp. (of uncertain species), since it is impossible to determine whether it belonged to the species B. altithorax itself (as there is no overlapping material between the two specimens). They based the skull's assignment to Brachiosaurus on its similarity to that of B. brancai, later known as Giraffatitan.   In 2019, American paleontologists Michael D. D'Emic and Matthew T. Carrano re-examined the Felch Quarry skull after having it further prepared and CT-scanned (while consulting historical illustrations that showed earlier states of the bones), and concluded that a quadrate bone and dentary tooth considered part of the skull by Carpenter and Tidwell did not belong to it. The quadrate is too large to articulate with the squamosal, is preserved differently from the other bones, and was found several meters away. The tooth does not resemble those within the jaws (as revealed by CT data), is larger, and was therefore assigned to Camarasaurus sp. (other teeth assignable to that genus are known from the quarry). They also found it most parsimonious to assign the skull to B. altithorax itself rather than an unspecified species, as there is no evidence of other brachiosaurid taxa in the Morrison Formation (and adding this and other possible elements to a phylogenetic analysis did not change the position of B. altithorax). 
A shoulder blade with coracoid 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 exceptionally large taxa, including the new genera Supersaurus and Ultrasaurus,  the latter renamed Ultrasauros shortly thereafter because another sauropod had already received the name.  Later study showed that the "ultrasaur" material mostly belonged to Supersaurus, though the shoulder blade did not. Because the holotype of Ultrasauros, a dorsal 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), was in 1996 assigned to a Brachiosaurus sp. (of uncertain species) by Brian Curtice and colleagues in 2009 Michael P. Taylor concluded that it could not be referred to B. altithorax.   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. 
In 2012, José Carballido and colleagues reported a nearly complete postcranial skeleton of a small juvenile approximately 2 meters (6 ft 7 in) in length. This specimen, nicknamed "Toni" and cataloged as SMA 0009, stems from the Morrison Formation of the Bighorn Basin in north-central Wyoming. Although originally thought to belong to a diplodocid, it was later reinterpreted as a brachiosaurid, probably belonging to B. altithorax.  In 2018, the largest sauropod foot ever found was reported from the Black Hills of Weston County, Wyoming. The femur is not preserved but comparisons suggest that it was about 2% longer than that of the B. altithorax holotype. Though possibly belonging to Brachiosaurus, the authors cautiously classified it as an indeterminate brachiosaurid. 
Formerly assigned species
Brachiosaurus brancai and Brachiosaurus 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 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 shared characters between Brachiosaurus brancai (which he now considered to include B. fraasi) and B. altithorax.  Taylor, in 2009, considered only four of these characters as valid six pertain to groups more inclusive 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 in 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 material was collected by the British Museum of Natural History's Tendaguru expedition, including a nearly complete skeleton (BMNH R5937) collected by F.W.H. Migeod in 1930. This specimen is now believed to represent a new species, awaiting description.  
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 ulnae 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, Gregory S. Paul published a new reconstruction of the skeleton of B. brancai, highlighting differences in proportion between it and B. altithorax. Chief among them was a distinction in the way the trunk vertebrae vary: they are fairly uniform in length in the African material, but vary widely in B. altithorax. Paul believed that the limb and girdle elements of both species were very similar, and therefore suggested they be separated not at genus, but only at subgenus level, as Brachiosaurus (Brachiosaurus) altithorax and Brachiosaurus (Giraffatitan) brancai.  Giraffatitan was raised to full genus level by George Olshevsky in 1991, while referring to the vertebral variation.  Between 1991 and 2009, the name Giraffatitan was almost completely disregarded by other researchers. 
A detailed 2009 study by Taylor of all material, including the limb and girdle bones, found that there are significant divergences 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 between Diplodocus and Barosaurus, and therefore argued that the African material should indeed be placed in its own genus—Giraffatitan—as Giraffatitan brancai.  An important contrast between the two genera is their overall body shape, with Brachiosaurus having a 23% longer dorsal vertebral series and a 20 to 25% longer and also taller tail.  The split was rejected by Daniel Chure in 2010,  but from 2012 onward most studies recognized the name Giraffatitan. 
In 1947, at Atalaia in Portugal, brachiosaurid remains were found in layers dating from the Tithonian. Albert-Félix de Lapparent and Georges Zbyszewski named them as the species Brachiosaurus atalaiensis in 1957.  Its referral to Brachiosaurus was doubted in the 2004 edition of The Dinosauria by Paul Upchurch, Barret, and Peter Dodson who listed it as an as yet unnamed brachiosaurid genus.  Shortly before the publication of the 2004 book, the species had been placed in its own genus Lusotitan by Miguel Telles Antunes and Octávio Mateus in 2003.  De Lapparent and Zbyszewski had 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 the lectotype this specimen includes twenty-eight 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 tilting upward indicate that Lusotitan is a brachiosaurid,  which was confirmed by some later studies, such as an analysis in 2013. 
In 1958, the French petroleum geologist F. Nougarède reported to have discovered fragmentary brachiosaurid remains in eastern Algeria, in the Sahara Desert.  Based on these, Albert-Félix de Lapparent described and named the species Brachiosaurus nougaredi in 1960. He indicated the discovery locality as being in the Late Jurassic–age Taouratine Series. He assigned the rocks to this age in part because of the presumed presence of Brachiosaurus.  A more recent review placed it in the "Continental intercalaire," which is considered to belong to the Albian age of the late Early Cretaceous, significantly younger. 
The type material moved to Paris consisted of a sacrum, weathered out at the desert surface, 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. 
"B." nougaredi was in 2004 considered to represent a distinct, unnamed brachiosaurid genus,  but a 2013 analysis by Philip D. Mannion and colleagues found that the remains possibly belong to more than one species, as they were collected far apart.  The metacarpals were concluded to belong to some indeterminate titanosauriform. The sacrum was reported lost in 2013. It was not analyzed and provisionally considered to represent an indeterminate sauropod, until such time that it could be relocated in the collections of the Muséum national d'histoire naturelle. Only four out of the five sacral vertebrae are preserved. The total original length was in 1960 estimated at 1.3 meters (4 ft 3 in), compared to 0.91 meters (3 ft 0 in) with B. altithorax.  This would make it larger than any other sauropod sacrum ever found, except those of Argentinosaurus and Apatosaurus. 
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 was somewhat lighter than the Brachiosaurus specimen given its proportional differences. In studies including estimates for both genera, Giraffatitan was estimated at 31.5 metric tons (34.7 short tons),  39.5 metric tons (43.5 short tons),  38.0 metric tons (41.9 short tons),  23.3 metric tons (25.7 short tons),  and 34.0 metric tons (37.5 short tons).   As with the main Brachiosaurus specimen, Giraffatitan specimen MB.R.2181 likely does not reflect the maximum size of the genus, as a fibula (specimen HM XV2) is 13% longer than that of MB.R.2181. 
Like all sauropod dinosaurs, Brachiosaurus was a quadruped 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 by bone resorption, greatly reducing the overall density of the body.   The neck is not preserved in the holotype specimen, but was very long even by sauropod standards in the closely related Giraffatitan, consisting of thirteen elongated cervical (neck) vertebrae.  The neck was held in a slight S-curve, with the lower and upper sections bent and a straight middle section.  Brachiosaurus likely shared with Giraffatitan the very elongated neck ribs, which ran down the underside of the neck, overlapping several preceding 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 trunk, lightening the distal neck portions.  
Brachiosaurus and Giraffatitan probably had a small shoulder hump between the third and fifth dorsal (back) vertebra, where the sideward- and upward-directed vertebral processes were longer, providing additional surface for neck muscle attachment.  The ribcage was deep compared to other sauropods.  Though 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 of other brachiosaurids.  This resulted in an inclined trunk with the shoulder much higher than the hips, and the neck exiting the trunk at a steep angle. The overall build of Brachiosaurus resembles a giraffe more than any other living animal.  In contrast, most other sauropods had a shorter forelimb than hindlimb the forelimb is especially short in contemporaneous diplodocoids. 
Brachiosaurus differed in its body proportions from the closely related Giraffatitan. The trunk was about 25–30% longer, resulting in a dorsal vertebral column longer than the humerus. Only a single complete caudal (tail) vertebra has been discovered, but its great height suggests that the tail was larger than in Giraffatitan. This vertebra had a much greater area for ligament attachment due to a broadened neural spine, indicating that the tail was also longer than in Giraffatitan, possibly by 20–25%.  In 1988, paleontologist Gregory S. Paul suggested that the neck of Brachiosaurus was shorter than that of Giraffatitan, but in 2009, paleontologist Mike P. Taylor pointed out that two cervical vertebrae likely belonging to Brachiosaurus had identical proportions.   Unlike Giraffatitan and other sauropods, which had vertically oriented forelimbs, the arms of Brachiosaurus appear to have been slightly sprawled at the shoulder joints, as indicated by the sideward orientation of the joint surfaces of the coracoids.  The humerus was less slender than that of Giraffatitan, while the femur had similar proportions. This might indicate that the forelimbs of Brachiosaurus supported a greater fraction of the body weight than is the case for Giraffatitan. 
Though the vertebral column of the trunk or torso is incompletely known, the back of Brachiosaurus most likely comprised twelve dorsal vertebrae this can be inferred from the complete dorsal vertebral column preserved in 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 much taller but only slightly longer. The centra (vertebral bodies), the lower part of the vertebrae, were more elongated and roughly circular in cross-section, while those of Giraffatitan were broader than tall. 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 upward. At their ends, these projections articulated with the ribs the articular surface was not distinctly triangular as in Giraffatitan. In side view, the upward-projecting neural spines stood vertically and were twice as wide at the base than at the top those of Giraffatitan tilted backward and did not broaden at their base. When seen in front or back view, the neural spines widened toward 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 back sides, the neural spines featured large, triangular and rugose surfaces, which in Giraffatitan were semicircular and much smaller. The various vertebral processes were connected by thin sheets or ridges of bone, which are 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, were conflated with the spinopostzygapophyseal laminae, which stretched between the neural spines and the articular processes at the back of the vertebrae, and therefore terminated at mid-height of the neural spines. In Giraffatitan, both laminae were not conflated, and the spinodiapophyseal laminae reached up to the top of the neural spines. Brachiosaurus is further distinguished from Giraffatitan in lacking three details in the laminae of the dorsal vertebrae that are unique to the latter genus. 
Air sacs not only invaded 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 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 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 had a short neural spine that was rectangular and tilted backward. In contrast to the second caudal vertebra of Giraffatitan, that of Brachiosaurus had a proportionally taller neural arch, making the vertebra around 30% taller. The centrum lacked depressions on its sides, in contrast to Giraffatitan. In front or back view, the neural spine broadened toward its tip to approximately three times its minimum width, but no broadening is apparent in Giraffatitan. The neural spines were also inclined backward by about 30°, more than in Giraffatitan (20°). The caudal ribs projected laterally and were not tilted backward as in Giraffatitan. The articular facets of the articular processes at the back of the vertebra were directed downward, while those of Giraffatitan faced more toward 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. 
Distinguishing features can also be found in the ilium of the pelvis. In Brachiosaurus, the ischiadic peduncle, a downward projecting extension connecting to the ischium, reaches farther downward than in Giraffatitan. While the latter genus had 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 ilium, Brachiosaurus had a pronounced tubercle that is absent in other sauropods. Of the hindlimb, the femur was very similar to that of Giraffatitan although slightly more robust, and measured 203 centimeters (80 in) long.  As in Giraffatitan, it was strongly elliptical in cross-section, being more than twice as wide in front or back view than in side view.  The fourth trochanter, a prominent bulge on the back side of the femoral shaft, was more prominent and located further downward. This bulge served as anchor point for the most important locomotory muscle, the caudofemoralis, which was situated in the tail and pulled the upper thigh backward when contracted. At the lower end of the femur, the pair of condyles did not extend backward as strongly as in Giraffatitan the two condyles were similar in width in Brachiosaurus but unequal in Giraffatitan. 
The dorsal and lateral temporal fenestrae (openings at the upper rear and sides of the skull) were large, perhaps due to the force imparted there by the massive jaw adductor musculature. The frontal bones on top of the skull were short and wide (similar to Giraffatitan), fused and connected by a suture to the parietal bones, which were also fused together. The surface of the parietals between the dorsal fenestrae was wider than that of Giraffatitan, but narrower than that of Camarasaurus. The skull differed from that of Giraffatitan in its U-shaped (instead of W-shaped) suture between frontal and nasal bones, a shape which appears more pronounced by the frontal bones extending forward 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 toward 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 upward. 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, relatively shallow, and less developed than that of Giraffatitan. It 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 trough.  
Each maxilla had space for about 14 or 15 teeth, whereas Giraffatitan had 11 and Camarasaurus 8 to 10. The maxillae contained replacement teeth that had 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 had larger teeth. The replacement teeth in the premaxilla had crinkled enamel, and the most complete of these teeth did not have denticles. It was somewhat spatulate (spoon-shaped), and had a longitudinal ridge. Each dentary had space for about 14 teeth. 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 in front of and below the fenestra in Camarasaurus and Shunosaurus.  
Riggs, in his preliminary 1903 description of the not yet fully prepared holotype specimen, considered Brachiosaurus to be an obvious member of the Sauropoda. To determine the validity of the genus, he compared it to the previously named genera Camarasaurus, Apatosaurus, Atlantosaurus, and Amphicoelias, whose validity he questioned given the lack of overlapping fossil material. Because of the uncertain relationships of these genera, little could be said about the relationships of Brachiosaurus itself.  In 1904, Riggs described the holotype material of Brachiosaurus in more detail, especially the vertebrae. He admitted that he originally had assumed a close affinity with Camarasaurus, but now decided that Brachiosaurus was more closely related to Haplocanthosaurus. Both genera shared a single line of neural spines on the back and had wide hips. Riggs considered the differences from other taxa significant enough to name a separate family, Brachiosauridae, of which Brachiosaurus is the namesake genus. According to Riggs, Haplocanthosaurus was the more primitive genus of the family while Brachiosaurus was a specialized form. 
When describing Brachiosaurus brancai and B. fraasi in 1914, Janensch observed that the unique elongation of the humerus was shared by all three Brachiosaurus species as well as the British Pelorosaurus. He also noted this feature in Cetiosaurus, where it was not as strongly pronounced as in Brachiosaurus and Pelorosaurus.  Janensch concluded that the four genera must have been closely related to each other, and in 1929 assigned them to a subfamily Brachiosaurinae within the family Bothrosauropodidae. 
During the twentieth century, several sauropods were assigned to Brachiosauridae, including Astrodon, Bothriospondylus, Pelorosaurus, Pleurocoelus, and Ultrasauros.  These assignments were often based on broad similarities rather than unambiguous synapomorphies, shared new traits, and most of these genera are currently regarded as dubious.   In 1969, in a study by R.F. Kingham, B. 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 not been accepted by many other authors.  Since the 1990s, computer-based cladistic analyses allow for postulating detailed hypotheses on the relationships between species, by calculating those trees that require the fewest evolutionary changes and thus are the most likely to be correct. Such cladistic analyses have cast doubt on the validity of the Brachiosauridae. In 1993, Leonardo Salgado suggested that they were an unnatural group into which all kinds of unrelated sauropods had been combined.  In 1997, he published an analysis in which species traditionally considered brachiosaurids were subsequent offshoots of the stem of a larger grouping, the Titanosauriformes, and not a separate branch of their own. This study also pointed out that B. altithorax and B. brancai did not have any synapomorphies, so that there was no evidence to assume they were particularly closely related. 
Many cladistic analyses have since suggested that at least some genera can be assigned to the Brachiosauridae, and that this group is a basal branch within the Titanosauriformes.  The exact status of each potential brachiosaurid varies from study to study. For example, a 2010 study by Chure and colleagues recognized Abydosaurus as a brachiosaurid together with Brachiosaurus, which in this study included B. brancai.  In 2009, Taylor noted multiple anatomical differences between the two Brachiosaurus species, and consequently moved B. brancai into its own genus, Giraffatitan. In contrast to earlier studies, Taylor treated both genera as distinct units in a cladistic analysis, finding them to be sister groups. Another 2010 analysis focusing on possible Asian brachiosaurid material found a clade including Abydosaurus, Brachiosaurus, Cedarosaurus, Giraffatitan, and Paluxysaurus, but not Qiaowanlong, the putative Asian brachiosaurid.  Several subsequent analyses have found Brachiosaurus and Giraffatitan not to be sister groups, but instead located at different positions on the evolutionary tree. A 2012 study by D'Emic placed Giraffatitan in a more basal position, in an earlier branch, than Brachiosaurus,  while a 2013 study by Philip Mannion and colleagues had it the other way around. 
The cladogram of the Brachiosauridae below follows that published by Michael D. D'Emic in 2012: 
Cladistic analyses also allow scientists to determine which new traits the members of a group have in common, their synapomorphies. According to the 2009 study by Taylor, B. altithorax shares with other brachiosaurids the classic trait of having an upper arm bone that is at least nearly as long as the femur (ratio of humerus length to femur length of at least 0.9). Another shared character is the very flattened femur shaft, its transverse width being at least 1.85 times the width measured from front to rear. 
It was believed throughout the nineteenth and early twentieth centuries that sauropods like Brachiosaurus were too massive to support their own weight on dry land, and instead lived partly submerged in water.  Riggs, affirming observations by John Bell Hatcher, was the first to defend in length that most sauropods were fully terrestrial animals in his 1904 account on Brachiosaurus, pointing out that their hollow vertebrae have no analogue in living aquatic or semiaquatic animals, and their long limbs and compact feet indicate specialization for terrestrial locomotion. Brachiosaurus would have been better adapted than other sauropods to a fully terrestrial lifestyle through its slender limbs, high chest, wide hips, high ilia and short tail. In its dorsal vertebrae the zygapophyses were very reduced while the hyposphene-hypanthrum complex was extremely developed, resulting in a stiff torso incapable of bending sideways. The body was only fit for quadrupedal movement on land.  Though Riggs' ideas were gradually forgotten during the first half of the twentieth century, the notion of sauropods as terrestrial animals has gained support since the 1950s, and is now universally accepted among paleontologists.   In 1990 the paleontologist Stephen Czerkas stated that Brachiosaurus could have entered water occasionally to cool off (thermoregulate). 
Ongoing debate revolves around the neck posture of brachiosaurids, with estimates ranging from near-vertical to horizontal orientations.  The idea of near-vertical postures in sauropods in general was popular until 1999, when Stevens and Parrish argued that the sauropod neck was not flexible enough to be held in an upright, S-curved pose, and instead was held horizontally.   Reflecting this research, various newspapers ran stories criticizing the Field Museum Brachiosaurus mount for having an upward curving neck. Museum paleontologists Olivier Rieppel and Christopher Brochu defended the posture in 1999, noting the long forelimbs and upward sloping backbone. They also stated that the most developed neural spines for muscle attachment being positioned in the region of the shoulder girdle would have permitted the neck to be raised in a giraffe-like posture. Furthermore, such a pose would have required less energy than lowering its neck, and the inter-vertebral discs would not have been able to counter the pressure caused by a lowered head for extended periods of time (though lowering its neck to drink must have been possible).  Some recent studies also advocated a more upward directed neck. Christian and Dzemski (2007) estimated that the middle part of the neck in Giraffatitan was inclined by 60–70 degrees a horizontal posture could be maintained only for short periods of time. 
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 less inclined neck, its head height may still have been over 9 meters (30 ft) above the ground.   It probably fed mostly on foliage above 5 meters (16 ft). This does not preclude the possibility that it also fed lower at times, between 3 to 5 meters (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 in a 2007 study.  Brachiosaurid feeding involved simple up-and-down jaw motion.  As in other sauropods, animals would have swallowed plant matter without further oral processing, and relied on hindgut fermentation for food processing.  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,  and 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 fed sixteen hours per day, biting off between a tenth and two-thirds of a kilogram, taking between one and six bites per minute, its daily food intake would have equaled roughly 1.5% of its body mass, comparable to the requirement of a modern elephant. 
As Brachiosaurus shared its habitat, the Morrison, with many other sauropod species, its specialization for feeding at greater heights would have been part of a system of niche partitioning, the various taxa thus avoiding direct 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 arms and lower shoulders, was not as well-adapted to high-browsing as Giraffatitan. 
It has been suggested that Brachiosaurus could rear on its hind legs to feed, using its tail for extra ground support.  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 its 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 only 33% more feeding height, compared to other sauropods, for which rearing 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, 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 as Witmer hypothesized. Hallett and Wedel therefore in 2016 rejected his interpretation and suggested that they were in fact placed at the top of the head, above the bony nostrils, as traditionally thought. The nostrils might have evolved their retracted position to allow the animal to breathe while drinking. 
The bony nasal openings of neosauropods like Brachiosaurus were large and placed on the top of their skulls. Traditionally, the fleshy nostrils of sauropods were thought to have been placed likewise on top of the head, roughly at the rear of the bony nostril opening, because these animals were erroneously thought to have been amphibious, using their large nasal openings as snorkels when submerged. The American paleontologist Lawrence M. Witmer rejected this reconstruction in 2001, pointing out 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 in an even more forward position, at the front of the narial fossa, the depression which extended far in front of the bony nostril toward the snout tip. 
Czerkas speculated on the function of the peculiar brachiosaurid nose, and pointed out that there was no conclusive way to determine where the nostrils where located, unless a head with skin impressions was found. He suggested that the expanded nasal opening would have made room for tissue related to the animal's ability to smell, which would have helped smell proper vegetation. He also noted that in modern reptiles, the presence of bulbous, enlarged, and uplifted nasal bones can be correlated with fleshy horns and knobby protuberances, and that Brachiosaurus and other sauropods with large noses could have had ornamental nasal crests. 
It has been proposed that sauropods, including Brachiosaurus, may have had proboscises (trunks) based on the position of the bony narial orifice, to increase their upward reach. Fabien Knoll and colleagues disputed this for Diplodocus and Camarasaurus in 2006, finding that the opening for the facial nerve in the braincase was small. The facial nerve was thus not enlarged as in elephants, where it is involved in operating the sophisticated musculature of the proboscis. However, Knoll and colleagues also noted that the facial nerve for Giraffatitan was larger, and could therefore not discard the possibility of a proboscis in this genus. 
Like other sauropods, Brachiosaurus was probably homeothermic (maintaining a stable internal temperature) and endothermic (controlling body temperature through internal means) at least while growing, meaning that it could actively control its body temperature ("warm-blooded"), producing the necessary heat through a high basic metabolic rate of its cells.  Russel (1989) used Brachiosaurus 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.  Sander (2010) found that these calculations were based on incorrect body mass estimates and faulty assumptions on the available cooling surfaces, as the presence of large air sacs was unknown at the time of the study. 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. 
The respiration system of sauropods, like that of birds, made use of air sacs. There was not a bidirectional airflow as with mammals, in which the lungs function as bellows, first inhaling and then exhaling air. Instead the air was sucked from the trachea into an abdominal air sac in the belly which then pumped it forward through the parabranchi, air loops, of the stiff lung. Valves prevented the air from flowing backward when the abdominal air sac filled itself again at the same time a cervical air sac at the neck base sucked out the spent air from the lung. Both air sacs contracted simultaneously to pump the used air out of the trachea. This procedure guaranteed a unidirectional airflow, the air always moving in a single forward direction in the lung itself. This significantly improved the oxygen intake and the release of carbon dioxide. Not only was dead air removed quickly but also the blood flow in the lung was counterdirectional in relation to the airflow, leading to a far more effective gas exchange. 
In sauropods, the air sacs did not simply function as an aid for respiration by means of air channels they were connected to much of the skeleton. These branches, the diverticula, via pneumatic openings invaded many bones and strongly hollowed them out. It is not entirely clear what the evolutionary benefit of this phenomenon was but in any case it considerably lightened the skeleton. They might also have removed excess heat to aid thermoregulation. 
In 2016, Mark Hallett and Mathew Wedel for the first time reconstructed the entire air sac system of a sauropod, using B. altithorax as an example of how such a structure might have been formed. In their reconstruction a large abdominal air sac was located between the pelvis and the outer lung side. As with birds, three smaller sacs assisted the pumping process from the underside of the breast cavity: at the rear the posterior thoracic air sac, in the middle the anterior thoracic air sac and in front the clavicular air sac, in that order gradually diminishing in size. The cervical air sac was positioned under the shoulder blade, on top of the front lung. The air sacs were via tubes connected with the vertebrae. Diverticula filled the various fossae and that formed depressions in the vertebral bone walls. These were again connected with inflexible air cells inside the bones. 
The ontogeny of Brachiosaurus has been reconstructed by Carballido and colleagues in 2012 based on Toni (SMA 0009), a postcranial skeleton of a young juvenile with an estimated total body length of just 2 meters (6.6 ft). This skeleton shares some unique traits with the B. altithorax holotype, indicating it is referable to this species. These commonalities 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. 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 ontogenetic 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: it is 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 had a ratio of just 0.33, the lowest known in the entire Neosauropoda. 
Another plausible ontogenetic change 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 dorsal vertebrae still completely lack these. 
Two traits are not so obviously linked to ontogeny. The neural spines of the rear dorsal vertebrae and the front sacral vertebrae are extremely compressed transversely, 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 toward 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, but 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. Furthermore, a very young juvenile of Europasaurus had 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 northernmost 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 were similar in tooth morphology to brachiosaurids, were also widespread and are known to have migrated seasonally, so this might have also been true for brachiosaurids. 
Other dinosaurs known from the Morrison Formation include the predatory theropods Koparion, Stokesosaurus, Ornitholestes, Ceratosaurus, Allosaurus and Torvosaurus, as well as 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. 
Riggs in the first instance tried to limit public awareness of the find. When reading a lecture to the inhabitants of Grand Junction, illustrated by lantern slides, on July 27, 1901, he explained the general evolution of dinosaurs and the exploration methods of museum field crews but did not mention that he had just found a spectacular specimen.  He feared that teams of other institutions might soon learn of the discovery and take away the best of the remaining fossils. A week later, his host Bradbury published an article in the local Grand Junction News announcing the find of one of the largest dinosaurs ever. On August 14, The New York Times brought the story.  At the time sauropod dinosaurs appealed to the public because of their great size, often exaggerated by sensationalist newspapers.  Riggs in his publications played into this by emphasizing the enormous magnitude of Brachiosaurus. 
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. 
Vertebrate study guide 3
-Convective Heat Exchange (C):
"Special" case of conduction:
Hind foot elongated, no fifth toe, meta and distal tarsels are fused to form tarsometatarsus
From Your Inner Reptile (PBS): The first mammals inherited from reptile ancestors - or are really re-purposed reptiles. Changes in skin, teeth, jaw/ear. Small burrowing mammals might have better survived a changing climate and meteor by being fossorial and in underground burrows. First hair was for sensory - whiskers to help in nocturnal world.
Synapsid Lineage = single lower fenestra in skull
Often mis-labeled in children's books as a dinosaur
Neural spines of trunk elongated into sail - unlikely used in display, found on both sexes, connected by web of skin
Temperature-regulating devices - were vascularized
Probably mostly found in tropical habitats
Pelycosaurs did not have epid scales, prob naked glandular skin
Pelycosaurs - generalized amniotes, no increased locom capacity or metabolic rate, most were carnivores
Therapsids - more derived and found in S. Hemisphere (Gondwana)
Be able to recognize the 2 lineages of non-mammal synapsids (pelyco is more primitive than therapsids)
Both may have started out as insectivores and then radiated into carnivores and herbiovores
Pelycosaurs - generalized amniotes, no increased locom capacity or metabolic rate, most were carnivores
D is gorgonopsid about size of Labrador retriever and Inner Fish video
Indicative of higher sustained activity and metabolic rates
Earliest known mammals have anatomy to suggest hair/fur. Derived cynodonts might have had fur, but unlikely for the earlier forms or ones that were large body size.
Early mammals were quite a bit smaller than cynodonts (rat size versus shrew size)
Perhaps need to evolve fur as insulation was not important until the small size of first mammals subject to heat loss
Derived Cynodonts had turbinates and were likely endothermic
Importance of Cynodonts:
Had nearly all mammalian features
Closest relatives of mammals
1) Size of temporal fenestra
2) Widening of zygomatic arch: jaw musculature
3) Evolution of teeth (multicusped)
4) Decrease in number of jaw bones
5) Secondary palate
Derived Feature of Cynodonts:
Reduction in overall body size.
Move from ectothermy to endothermy
7) Enlarged infraorbital foramen - importance?
8) Evidence of turbinates
Cynodonts probably were oviparous.
Cynodonts may have had whiskers (based on channels in jaw to hold vessels), but not fur = explain body size
High metabolic rates - some cynodonts
In addition, the cynodonts began to develop tricuspid "cusps" on the occusal surface of "double rooted" teeth resulting in a much greater ability to chew food more efficiently
-Cloaca - single opening for reproduction and waste
-Lack teeth as adults
Leathery bill (echidna) or beak (platypus) for sensory
-One of the few venomous mammals: male platypus has venomous spur on hind leg echidnas have non-functional spurs.
-Only extant mammals that lay eggs
-Egg is retained for some time within mother
-Lactate, but no defined nipples. Excrete milk from mammary glands through skin openings.
-Low reproductive rate, long parental care
-Two primary divisions marsupials:
-American (100 spp.)
-Australian marsupials (>200 spp.)
Placentals" somewhat of a misnomer b/c marsupials have a placenta too
Placental mammals all bear live young, which are nourished before birth in the mother's uterus through a specialized embryonic organ attached to the uterus wall, the placenta. The placenta is derived from the same membranes that surround the embryos in the amniote eggs of reptiles, birds, and monotreme. mammals. The term "placental mammals" is somewhat of a misnomer because marsupials also have placentae. The difference is that the placenta of marsupials is very short-lived and does not make as much of a contribution to fetal nourishment as it does in eutherians, as "placental mammals" are known scientifically.
Mammary glands in monotremes, marsupials, and placentals
-Evolved from glands associated with hair follicles, probably evolved in early synapsids (before mammal) because have glandular skin and not scaly skin
-Monotremes don't have nipples, milk associated with hairs in skin
Males have nipples in placentals because sexual differentiation occurs during gestation but first sexes look similar until formation of gonads and hormone development
In Marsupials, males don't have pouches or nipples because those develop before gonad formation and hormones
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Vol 286, Issue 5443
12 November 1999
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By Paul C. Sereno , Allison L. Beck , Didier B. Dutheil , Hans C. E. Larsson , Gabrielle H. Lyon , Bourahima Moussa , Rudyard W. Sadleir , Christian A. Sidor , David J. Varricchio , Gregory P. Wilson , Jeffrey A. Wilson
Science 12 Nov 1999 : 1342-1347
How long was the torso of Dreadnoughtus?
September 15, 2014
In a comment on the last post, on the mass of Dreadnoughtus, Asier Larramendi wrote:
The body mass should be considerably lower because the reconstructed column don’t match with published vertebrae centra lengths. 3D reconstruction also leaves too much space between vertebrae. The reconstruction body trunk is probably 15-20% longer than it really was. Check the supplementary material: http://www.nature.com/srep/2014/140904/srep06196/extref/srep06196-s1.pdf
So I did. The table of measurements in the supplementary material is admirably complete. For all of the available dorsal vertebrae except D9, which I suppose must have been too poorly preserved to measure the difference, Lacovara et al. list both the total centrum length and the centrum length minus the anterior condyle. Centrum length minus the condyle is what in my disseration I referred to as “functional length”, since it’s the length that the vertebra actually contributes to the articulated series, assuming that the condyle of one vertebra sticks out about as far as the cotyle is recessed on the next vertebra. Here are total lengths/functional lengths/differences for the seven preserved dorsals, in mm:
- D4 – 400/305/95
- D5 – 470/320/150
- D6 – 200/180/20
- D7 – 300/260/40
- D8 – 350/270/80
- D9 – 410/ – / –
- D10 – 330/225/105
The average difference between functional length and total length is 82 mm. If we apply that to D9 to estimate it’s functional length, we get 330mm. The summed functional lengths of the seven preserved vertebrae are then 1890 mm. What about the missing D1-D3? Since the charge is that Lacovara et al. (2014) restored Dreadnoughtus with a too-long torso, we should be as generous as possible in estimating the lengths of the missing dorsals. In Malawisaurus the centrum lengths of D1-D3 are all less than or equal to that of D4, which is the longest vertebra in the series (Gomani 2005: table 3), so it seems simplest here to assign D1-D3 functional lengths of 320 mm. That brings the total functional length of the dorsal vertebral column to 2850 mm, or 2.85 m.
At this point on my first pass, I was thinking that Lacovara et al. (2014) were in trouble. In the skeletal reconstruction that I used for the GDI work in the last post, I measured the length of the dorsal vertebral column as 149 pixels. Divided by 36 px/m gives a summed dorsal length of 4.1 m. That’s more than 40% longer than the summed functional lengths of the vertebrae calculated above (4.1/2.85 = 1.44). Had Lacovara et al. really blown it that badly?
Before we can rule on that, we have to estimate how much cartilage separated the dorsal vertebrae. This is a subject of more than passing interest here at SV-POW! Towers–the only applicable data I know of are the measurements of intervertebral spacing in two juvenile apatosaurs that Mike and I reported in our cartilage paper last year (Taylor and Wedel 2013: table 3, and see this post). We found that the invertebral cartilage thickness equaled 15-24% of the length of the centra.* For the estimated 2.85-meter dorsal column of Dreadnoughtus, that means 43-68 cm of cartilage (4.3-6.8 cm of cartilage per joint), for an in vivo dorsal column length of 3.28-3.53 meters. That’s still about 15-20% shorter than the 4.1 meters I measured from the skeletal recon–and, I must note, exactly what Asier stated in his comment. All my noodling has accomplished is to verify that his presumably off-the-cuff estimate was spot on. But is that a big deal?
Visually, a 20% shorter torso makes a small but noticeable difference. Check out the original reconstruction (top) with the 20%-shorter-torso version (bottom):
FWIW, the bottom version looks a lot more plausible to my eye–I hadn’t realized quite how weiner-dog-y the original recon is until I saw it next to the shortened version.
In terms of body mass, the difference is major. You’ll recall that I estimated the torso volume of Dreadnoughtus at 32 cubic meters. Lopping off 20% means losing 6.4 cubic meters–about the same volume as a big bull elephant, or all four of Dreadnoughtus‘s limbs put together. Even assuming a low whole-body density of 0.7 g/cm^3, that’s 4.5 metric tons off the estimated mass. So a
30-ton Dreadnoughtus is looking more plausible by the minute.
For more on how torso length can affect the visual appearance and estimated mass of an animal, see this post and Taylor (2009).
* I asked Mike to do a review pass on this post before I published, and regarding the intervertebral spacing derived from the juvenile apatosaurs, he wrote:
That 15-24% is for juveniles. For the cervicals of adult Sauroposeidon we got about 5%. Why the differences? Three reasons might be relevant: 1, taxonomic difference between Sauroposeidon and Apatosaurus 2, serial difference between neck and torso 3, ontogenetic difference between juvenile and adult. By applying the juvenile Apatosaurus dorsal measurement directly to the adult Dreadnoughtus dorsals, you’re implicitly assuming that the adult/juvenile axis is irrelevant (which seems unlikely to me), that the taxonomic axis is (I guess) unknowable, and that the cervical/dorsal distinction is the only one that matter.
That’s a solid point, and it deserves a post of its own, which I’m already working on. For now, it seems intuitively obvious to me that we got a low percentage on Sauroposeidon simply because the vertebrae are so long. If the length-to-diameter ratio was 2.5 instead of 5, we’d have gotten 10%, unless cartilage thickness scales with centrum length, which seems unlikely. For a dorsal with EI of 1.5, cartilage thickness would then be 20%, which is about what I figured above.
Now, admittedly that is arm-waving, not science (and really just a wordy restatement of his point #2). The obvious thing to do is take all of our data and see if intervertebral spacing is more closely correlated with centrum length or centrum diameter. Now that it’s occurred to me, it seems very silly not to have done that in the actual paper. And I will do that very thing in an upcoming post. For now I’ll just note three things:
- As you can see from figure 15 in our cartilage paper, in the opisthocoelous anterior dorsals of CM 3390, the condyle of the posterior vertebra is firmly engaged in the cotyle of the anterior one, and if anything the two vertebrae look jammed together, not drifted apart. But the intervertebral spacing as a fraction of centrum length is still huge (20+4%) because the centra are so short.
- Transferring these numbers to Dreadnoughtus only results in 4.3-6.8 cm of cartilage between adjacent vertebrae, which does not seem unreasonable for a 30- or 40-ton animal with dorsal centra averaging 35 cm in diameter. If you asked me off the cuff what I thought a reasonable intervertebral spacing was for such a large animal, I would have said 3 or 4 inches (7.5 to 10 cm), so the numbers I got through cross-scaling are actually lower than what I would have guessed.
- Finally, if I’ve overestimated the intervertebral spacing, then the actual torso length of Dreadnoughtus was even shorter than that illustrated above, and the volumetric mass estimate would be smaller still. So in going with relatively thick cartilage, I’m being as generous as possible to the Lacovara et al. (2014) skeletal reconstruction (and indirectly to their super-high allometry-derived mass estimate), which I think is only fair.
The sauropod Huabeisaurus allocotus was excavated from Upper Cretaceous sediments of northeast China in the 1990 s. The holotype of Huabeisaurus is a partially articulated individual composed of teeth, representative elements from all regions of the axial column (cervical, dorsal, sacral, and caudal vertebrae), ribs, complete pectoral and pelvic girdles, and nearly complete limbs. Due to its relative completeness, Huabeisaurus represents an important taxon for understanding sauropod evolution in Asia.
The original description of the species noted strong similarities between the osteology of Huabeisaurus and other Cretaceous East Asian sauropods, and in general, previous studies have pointed to some East Asian Cretaceous sauropod (e.g., Nemegtosaurus, Phuwiangosaurus) as the sister taxon of Huabeisaurus. In the 13 years since the original description of Huabeisaurus, 17 new sauropod species have been erected from the Cretaceous of East Asia (see lists in , ). Many authors have noted similarities among Cretaceous East Asian sauropods, often suggesting that several of these taxa belong to a clade grounded on a genus with well-known anatomy (e.g., Nemegtosauridae, – Opisthocoelicaudinae,  Euhelopodidae, ,  see  for further discussion). Cladistic support was recently presented for a Euhelopodidae that consisted of exclusively Cretaceous-aged members , in contrast with traditional studies and early cladistic analyses that posited the existence of a Euhelopodidae with Jurassic forms (see ,  for detailed discussion). Both earlier and later analyses suggest some degree of endemism in East Asia, though its temporal duration remains uncertain. On a broader scale, an interesting evolutionary pattern has been recognized wherein all pre-Jurassic Cretaceous Asian sauropods lie outside of Neosauropoda, whereas all Cretaceous Asian sauropods are titanosauriforms . Refining and explaining these paleobiogeographic patterns through time rests on detailed comparisons and comprehensive phylogenetic studies including East Asian sauropods, which are currently lacking.
With the aim of presenting comparative osteological data for Huabeisaurus, we examined the hypodigm firsthand at the Shijiazhuang University Museum. Below, we redescribe the anatomy of Huabeisaurus, highlighting similarities and differences with other Cretaceous East Asian sauropods. Based on synapomorphies recovered by existing cladistic datasets, we place Huabeisaurus in the wider context of sauropod evolution by exploring its lower level affinities. Finally, we compare the disparity of tooth shapes among derived sauropod clades, noting the exceptional range of shapes found within Euhelopodidae.
We thank Zhenhua Xiao and Dachun Wang of the Zhuzhou Land Resource Bureau, and Daohe Xi, Yalan Liu and Jun Lei of the Zhuzhou Museum, for their hospitality, and Paul Upchurch for his constructive comments on the possible affinities of the specimens described in this paper. We thank Philip Mannion and Stephen Poropat for their detailed reviews of a previous version of this paper and Graciela Piñeiro for her constructive suggestions. We thank the editor Hans-Dieter Sues, and the reviewers John Whitlock and Alexander Averianov, for their useful comments on the manuscript.
The authors declare there are no competing interests.
Fenglu Han conceived and designed the experiments, performed the experiments, analyzed the data, contributed reagents/materials/analysis tools, prepared figures and/or tables, authored or reviewed drafts of the paper, approved the final draft.
Xing Xu and Corwin Sullivan conceived and designed the experiments, authored or reviewed drafts of the paper, approved the final draft.
Leqing Huang conceived and designed the experiments, contributed reagents/materials/analysis tools, prepared figures and/or tables, approved the final draft.
Yu Guo performed the experiments, prepared figures and/or tables, approved the final draft.
Rui Wu analyzed the data, prepared figures and/or tables, approved the final draft.
The following information was supplied regarding data availability:
A small cervical vertebra ZGT002, a partial cervical centra ZGT012, two articulated cervical centra ZGT005, two partial cervical ribs ZGT044 and ZGT013, a caudal vertebra ZGT003, a partial large humerus ZGT056-060, and a small humerus ZGT089 are stored in the Bureau of Land and Resources of Zhuzhou City, Zhuzhou, Hunan Province, China.
A partial scapula ZMW143, a complete left ischium ZMW148, a complete fibula ZMW51-57, a complete pedal ungual ZMW013 are stored in the Zhuzhou Museum, Zhuzhou, Hunan Province, China.
This research was funded by the National Natural Science Foundation of China (No. 41502011) to Fenglu Han and (No. 41688103) Xing Xu, the International Partnership Program of Chinese Academy of Sciences (No. 132311KYSB20180016) to Xing Xu, the Regional Geological Survey of Chengbu-Nanxiong Area in Nanling-Geotectonic Framework and Resource Background Investigation of Hezhou-Chenzhou (No. DD20190811) to Fenglu Han, the Natural Science Foundation of Hunan Province (No. 2017JJ3139) to Leqing Huang, the Natural Sciences and Engineering Research Council of Canada (Discovery Grant RGPIN-2017-06246), and start-up funding awarded by the University of Alberta to Corwin Sullivan. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.