| Brontosaurus | |
|---|---|
 | |
| Holotype specimen ofB. excelsus (YPM 1980),Peabody Museum of Natural History, as remounted in 2020 | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | †Sauropodomorpha |
| Clade: | †Sauropoda |
| Superfamily: | †Diplodocoidea |
| Family: | †Diplodocidae |
| Subfamily: | †Apatosaurinae |
| Genus: | †Brontosaurus Marsh, 1879 |
| Type species | |
| †Brontosaurus excelsus Marsh, 1879 | |
| Referred species | |
| Synonyms | |
Synonyms ofB. excelsus
Synonyms ofB. parvus
Synonyms ofB. yahnahpin
| |
Brontosaurus (/ˌbrɒntəˈsɔːrəs/;[1][2] meaning "thunder lizard" from theGreek wordsβροντή,brontē "thunder" andσαῦρος,sauros "lizard") is agenus ofherbivoroussauropoddinosaur that lived in present-dayUnited States during theLate Jurassic period. It was described by AmericanpaleontologistOthniel Charles Marsh in 1879, thetype species being dubbedB. excelsus, based on a partial skeleton lacking askull found inComo Bluff,Wyoming. In subsequent years, two morespecies ofBrontosaurus were named:B. parvus in 1902 andB. yahnahpin in 1994.Brontosaurus lived about 156 to 146 million years ago (mya) during theKimmeridgian andTithonian ages in theMorrison Formation of what is nowUtah and Wyoming. For decades, the animal was thought to have been ataxonomic synonym of its close relativeApatosaurus, but a 2015 study by Emmanuel Tschopp and colleagues found it to be distinct.[3] It has seen widespread representation in popular culture, being the archetypal "long-necked" dinosaur in general media.
Theanatomy ofBrontosaurus is well known, with fossils demonstrating that it was large, long-necked, andquadrupedal with a long tail terminating in a whip-like structure. Thecervical vertebrae are notably extremely robust and heavily-built, in contrast to its lightly built relativesDiplodocus andBarosaurus. The forelimbs were short and stout whereas the hindlimbs were elongated and thick, supported respectively by a heavily builtshoulder girdle andpelvis. Several size estimates have been made, with the largest speciesB. excelsus reaching up to 21–22 m (69–72 ft) from head to tail and weighing in at 15–17 t (17–19 short tons), whereas the smallerB. parvus only got up to 19 m (62 ft) long. Juvenile specimens ofBrontosaurus are known, with younger individuals growing rapidly to adult size in as little as 15 years.
Brontosaurus has been classified within the familyDiplodocidae, which was a group of sauropods that had shorter necks and longer tails compared to other families likebrachiosaurs andmamenchisaurs. Diplodocids first evolved in theMiddle Jurassic but peaked in diversity during the Late Jurassic with forms likeBrontosaurus before becoming extinct in the Early Cretaceous.Brontosaurus is a genus in the subfamilyApatosaurinae, which includes only it andApatosaurus, which are distinguished by their firm builds and thick necks. Although Apatosaurinae was named in 1929, the group was not usedvalidly until an extensive 2015 paper, which foundBrontosaurus to be valid. However, the status ofBrontosaurus is still uncertain, with some paleontologists still considering it a synonym ofApatosaurus.
Being from the Morrison Formation,Brontosaurus coexisted with a menagerie of other taxa such as the sauropodsDiplodocus, Barosaurus, andBrachiosaurus; herbivorousornithischiansStegosaurus,Dryosaurus, andNanosaurus; as well as the carnivoroustheropodsAllosaurus,Marshosaurus andCeratosaurus. This formation was a hotspot of sauropod biodiversity, with over 16 recognized genera, which resulted in niche partitioning between different sauropods.
The discovery of a large and fairly completesauropod skeleton was announced in 1879 byOthniel Charles Marsh, a professor of paleontology atYale University. The specimen was collected fromMorrison Formation rocks atComo Bluff,Wyoming byWilliam Harlow Reed. He identified it as belonging to an entirely new genus and species, which he namedBrontosaurus excelsus,[4] meaning "thunder lizard", from the Greekbrontē/βροντη meaning "thunder" andsauros/σαυρος meaning "lizard",[5] and from theLatinexcelsus, "noble" or "high".[6] By this time, the Morrison Formation had become the center of theBone Wars, a fossil-collecting rivalry between Marsh and another early paleontologist,Edward Drinker Cope. Because of this, the publications and descriptions of taxa by Marsh and Cope were rushed at the time.[7]Brontosaurus excelsus' type specimen (YPM 1980) was one of the most complete sauropod skeletons known at the time, preserving many of the characteristic but fragile cervical vertebrae.[8] Marsh believed thatBrontosaurus was a member of theAtlantosauridae, a clade of sauropod dinosaurs he named in 1877 that also includedAtlantosaurus andApatosaurus.[8] A year later in 1880, another partial postcranialBrontosaurus skeleton was collected near Como Bluff by Reed,[9][10] including well-preserved limb elements.[3] Marsh named this second skeletonBrontosaurus amplus ("large thunder lizard") in 1881,[10] but it was considered a synonym ofB. excelsus in 2015.[3]
In August 1883,Marshall P. Felch collected a disarticulated partialskull (USNM V 5730) of a sauropod further south in the Felch Quarry atGarden Park,Colorado and sent the specimen to Yale.[11][12] Marsh referred the skull toB. excelsus,[11][13] later featuring it in a skeletal reconstruction of theB. excelsus type specimen in 1891[13] and the illustration was featured again in Marsh's landmark publication,The Dinosaurs of North America, in 1896.[8] At theYale Peabody Museum, the skeleton ofBrontosaurus excelsus was mounted in 1931 with a skull based on the Marsh reconstruction of the Felch Quarry skull.[14] While at the time most museums were usingCamarasaurus casts for skulls, the Peabody Museum sculpted a completely different skull based on Marsh's recon.[14][11] Marsh's skull was inaccurate for several other reasons: it included forward-pointing nasals, something truly different to any other dinosaur, and fenestrae differing from the drawing and other skulls. The mandible was based on aCamarasaurus'.[14] In 1998, the Felch Quarry skull that Marsh included in his 1896 skeletal restoration was suggested to belong toBrachiosaurus instead[11] and this was supported in 2020 with a redescription of thebrachiosaurid material found at the Felch Quarry.[12]
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During aCarnegie Museum expedition to Wyoming in 1901, William Harlow Reed collected anotherBrontosaurus skeleton, a partial postcranial skeleton of a young juvenile (CM 566), including partial limbs. However, this individual was found intermingled with a fairly complete skeleton of an adult (UW 15556).[15] The adult skeleton specifically was very well-preserved, bearing many cervical (neck) and caudal (tail) vertebrae, and is the most complete definite specimen of the species.[3] The skeletons were granted a new genus and species name,Elosaurus parvus ("little field lizard"), by Olof A. Peterson andCharles Gilmore in 1902.[15] Both of the specimens came from the Brushy Basin Member of the Morrison Formation. The species was later transferred toApatosaurus by several authors[16][17] In 2008, a nearly complete postcranial skeleton of anapatosaurine was collected in Utah by crews working forBrigham Young University (BYU 1252-18531) where some of the remains are currently on display.[3] The skeleton is undescribed, but many of the features of the skeleton are shared withA. parvus.[3] The species was placed inBrontosaurus Tschoppet al. in 2015 during their comprehensive study ofDiplodocidae.[18][3]
In the 1903 edition ofGeological Series of the Field Columbian Museum,Elmer Riggs argued thatBrontosaurus was not different enough fromApatosaurus to warrant a separate genus, so he created the new combinationApatosaurus excelsus for it. Riggs stated that "In view of these facts the two genera may be regarded as synonymous. As the term 'Apatosaurus' has priority, 'Brontosaurus' will be regarded as a synonym".[19] Nonetheless, before the mounting of the American Museum of Natural History specimen,Henry Fairfield Osborn chose to label the skeleton "Brontosaurus", though he was a strong opponent of Marsh and his taxa.[14][20]
In 1905, theAmerican Museum of Natural History (AMNH) unveiled the first-ever mounted skeleton of a sauropod, a composite specimen (mainly made of bones from AMNH 460) that they referred to asBrontosaurus excelsus. The AMNH specimen was very complete, only missing the feet, from the specimen AMNH 592 were added to the mount, lower leg and shoulder bones, added from AMNH 222, and tail bones, added from AMNH 339.[21] To finish the mount, the rest of the tail was fashioned to appear as Marsh believed it should, which meant it had too few vertebrae. In addition, a sculpted model of what the museum felt the skull of this massive creature might have looked like was placed on the skeleton. This was not a delicate skull like that ofDiplodocus, which would later turn out to be more accurate, but was based on "the biggest, thickest, strongest skull bones, lower jaws, and tooth crowns from three different quarries".[22][19][23][24] These skulls were likely those ofCamarasaurus, the only other sauropod of which good skull material was known at the time. The mount construction was overseen by Adam Hermann, who failed to findBrontosaurus skulls. Hermann was forced to sculpt a stand-in skull by hand.Henry Fairfield Osborn noted in a publication that the skull was "largely conjectural and based on that ofMorosaurus" (nowCamarasaurus).[14]
In 1909, anApatosaurus skull was found, during the first expedition to what would become the Carnegie Quarry atDinosaur National Monument, led by Earl Douglass. The skull was found a few meters away from a skeleton (specimen CM 3018) identified as the new speciesApatosaurus louisae. The skull was designated CM 11162 and was very similar to the skull ofDiplodocus. It was accepted as belonging to theApatosaurus specimen by Douglass and Carnegie Museum directorWilliam J. Holland, although other scientists, most notably Osborn, rejected this identification. Holland defended his view in 1914 in an address to thePaleontological Society of America, yet he left the Carnegie Museum mount headless. While some thought Holland was attempting to avoid conflict with Osborn, others suspected that Holland was waiting until an articulated skull and neck were found to confirm the association of the skull and skeleton.[14] After Holland's death in 1934, a cast of aCamarasaurus skull was placed on the mount by museum staff.[20]
No apatosaurine skull was mentioned in the literature until the 1970s when John Stanton McIntosh and David Berman redescribed the skulls ofDiplodocus andApatosaurus in 1975.[24] They found that though he never published his opinion, Holland was almost certainly correct in thatApatosaurus andBrontosaurus had aDiplodocus-like skull.[24] According to them, many skulls long thought to belong toDiplodocus might instead be those ofApatosaurus.[24] They reassigned multiple skulls toApatosaurus based on associated and closely associated vertebrae.[24] Though they supported Holland,Apatosaurus was falsely theorized to possibly have possessed aCamarasaurus-like skull, based on a disarticulatedCamarasaurus-like tooth found at the precise site where anApatosaurus specimen was found years before.[24] However, this tooth does not come fromApatosaurus.[25] On October 20, 1979, after the publications by McIntosh and Berman, the first skull of anApatosaurus was mounted on a skeleton in a museum, that of the Carnegie.[20] In 1995, the American Museum of Natural History followed suit, and unveiled their remounted skeleton (now labelledApatosaurus excelsus) with a corrected tail and a new skull cast fromA. louisae.[21] In 1998,Robert T. Bakker referred a skull and mandible of an apatosaurine from Como Bluff toBrontosaurus excelsus (TATE 099-01), though the skull is still undescribed.[26] In 2011, the first specimen ofApatosaurus where a skull was found articulated with its cervical vertebrae was described. This specimen,CMC VP 7180, was found to differ in both skull and neck features fromA. louisae, and the specimen was found to have a majority of features related to those ofA. ajax.[27]
Another specimen of an Apatosaurine now referred toBrontosaurus was discovered in 1993 by theTate Geological Museum, also from the Morrison Formation of central Wyoming. The specimen consisted of a partial postcranial skeleton, including a complete manus and multiple vertebrae, and was described by James Filla and Pat Redman a year later.[26] Filla and Redman named the specimenApatosaurus yahnahpin ("yahnahpin-wearing deceptive lizard"), butRobert T. Bakker gave it the genus nameEobrontosaurus in 1998.[26] Bakker believed thatEobrontosaurus was the direct predecessor toBrontosaurus,[26] although Tschoppet al.'s phylogenetic analysis placedB. yahnahpin as the basalmost species ofBrontosaurus.[3]
Almost all 20th-century paleontologists agreed with Riggs that allApatosaurus andBrontosaurus species should be classified in a single genus. According to the rules of theICZN, which governs the scientific names of animals, the nameApatosaurus, having been published first, had priority;Brontosaurus was considered ajunior synonym and was therefore discarded from formal use.[28][29][30][31] Despite this, at least one paleontologist—Robert T. Bakker—argued in the 1990s thatA. ajax andA. excelsus are sufficiently distinct that the latter continues to merit a separate genus.[26] In 2015, an extensive study of diplodocid relationships by Emanuel Tschopp, Octavio Mateus, and Roger Benson concluded thatBrontosaurus was indeed a valid genus of sauropod distinct fromApatosaurus. The scientists developed a statistical method to more objectively assess differences between fossil genera and species and concluded thatBrontosaurus could be "resurrected" as a valid name. They assigned two formerApatosaurus species,A. parvus, andA. yahnahpin, toBrontosaurus, as well as the type speciesB. excelsus.[3] The publication was met with some criticism from other paleontologists, including Michael D'Emic,[32]Donald Prothero, who criticized the mass media reaction to this study as superficial and premature,[33] and many othersbelow. Some paleontologists, such asJohn andRebecca Foster, continue to considerBrontosaurus as a synonym ofApatosaurus.[34][35]
Brontosaurus was a large, long-necked,quadrupedal animal with a long, whip-like tail, and forelimbs that were slightly shorter than its hindlimbs. The largest species,B. excelsus, measured up to 21–22 m (69–72 ft) long from head to tail and weighed up to 15–17 t (17–19 short tons); other species were smaller, measuring 19 m (62 ft) long and weighing 14 t (15 short tons).[36][37] The skull ofBrontosaurus has not been found but was probably similar to the skull of the closely relatedApatosaurus. Several skulls ofApatosaurus have been found, all of which are very small in proportion to the body. Their snouts were squared off and low, in contrast tomacronarians'.[38] Jaws ofApatosaurus and other diplodocids were lined with spatulate (chisel-like) teeth which were adapted for herbivory.[25][27]
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Like those of otherdiplodocids, the vertebrae of the neck were deeply bifurcated on the dorsal side; that is, they carried paired spines, resulting in a wide and deep neck.[39] The spine and tail consisted of 15 cervicals, ten dorsals, five sacrals, and about 82 caudals, based onApatosaurus. The number of caudal vertebrae has been noted to vary, even within a species. Vertebrae in the neck, torso, and sacrum of sauropods bore largepneumatic foramina on their lateral sides.[10] These are used to lighten the bones which aided in keeping the animal lighter. Within the vertebrae as well, smooth bone walls in addition todiverticula would make pockets of air to keep the bones light.[40] Similar structures are observable in birds and large mammals.[41] The cervical vertebrae were stouter than those of other diplodocids, as inApatosaurus. On the lateral sides of the cervicals, apatosaurines had well-developed and thickparapophyses (extensions on the lateral sides of the vertebrae that attached to cervical ribs) which would point ventrally under thecentrum. These parapophyses in conjunction with densediapophyses andcervical ribs were strong anchors for neck muscles, which could sustain extreme force.[42] The cervicals were also more boxy than in other sauropods due to their truncatedzygapophyses and tall build.[43][3] These vertebrae are triangular in anterior view, whereas they most often are rounded or square in genera likeCamarasaurus. Despite its pneumaticy, the neck ofBrontosaurus is thought to have been double the mass of that of other diplodocids due to the former’s sturdiness.[42]Brontosaurus differs fromApatosaurus in that the base of the posterior dorsal vertebrae'sneural spines are longer than they are wide. The cervicals of species withinBrontosaurus also vary, such as the lack oftubercules on the neural spines ofB. excelsus and the lateral expansion of unbifurcated neural spines inB. parvus.[3]
Its dorsal vertebrae had short centra with largefossae (shallow excavations) on their lateral sides, though not as extensively as the cervicals’.[44] Neural canals, which contain thespinal cord of the vertebral column, are ovate and large in the dorsals. The diapophyses protrude outward and curve downward in a hook-shape. Neural spines are thick in anterior-posterior view with a bifurcate top.[3] The neural spines of the dorsals would increase in height further towards the tail, creating an arched back. Apatosaurine neural spines compose more than half the height of the vertebrae. Medial surfaces of neural spines are gently rounded inB. yahnahpin, whereas in otherB. spp. they are not.[3] The dorsal ribs are not fused or tightly attached to their vertebrae, instead being loosely articulated.[22] Tendorsal ribs are on either side of the body.[19] Expanded excavations within thesacrum are present making it into a hollow cylinder-shape. Sacral neural spines are fused together into a thin plate. The posteriormost caudal vertebra was lightly fused to the sacral vertebrae, becoming part of the plate. Internally, theneural canal was enlarged.[45][46][19] The shape of the tail was typical of diplodocids, being comparatively slender, due to the vertebral spines rapidly decreasing in height the farther they are from the hips. As in other diplodocids, the last portion of the tail ofBrontosaurus possessed a whip-like structure.[22] The tail also bears an extensive air-sac system to lighten its weight, as observed in specimens ofB. parvus.[47][48]
Severalscapulae are known fromBrontosaurus, all of which are long and thin with relatively elongated shafts.[45] One of traits that distinguishesBrontosaurus andApatosaurus is the presence of a depression on the posterior face of the scapula, which the latter lacks. The scapula ofBrontosaurus also has a rounded extension off of its edge, a characteristic unique toBrontosaurus among Apatosaurinae.[3] Thecoracoid anatomy is closely akin to that ofApatosaurus, with a quadratic outline in dorsal view.Sterna have been preserved in some specimens ofBrontosaurus, which display an oval outline.[10] The hip bones include robustilia and the fusedpubes andischia. The limb bones were also very robust,[49] with thehumerus resembling that ofCamarasaurus, and those ofB. excelsus being nearly identical to those ofApatosaurus ajax. The humerus had a thinbone shaft and larger transverse ends. Its anterior end bears a largedeltopectoral crest, which was on the extremities of the bone.[50] Charles Gilmore in 1936 noted that previous reconstructions erroneously proposed that theradius andulna could cross, when in life they would have remained parallel.[22]Brontosaurus had a single large claw on each forelimb which faced towards the body, whereas the rest of thephalanges lackedunguals.[51] Even by 1936, it was recognized that no sauropod had more than one hand claw preserved, and this one claw is now accepted as the maximum number throughout the entire group.[22][52] The metacarpals are elongated and thinner than the phalanges, bearing boxy articular ends on its proximal and distal faces.[8] The single front claw bone is slightly curved and squarely shortened on the front end. The phalangeal formula is 2-1-1-1-1, meaning the innermost finger (phalanx) on the forelimb has two bones and the next has one. The single manual claw bone (ungual) is slightly curved and squarely truncated on the anterior end. Proportions of the manus bones vary within Apatosaurinae as well, withB. yahnahpin's ratio of longest metacarpal to radius length around 0.40 or greater compared to a lower value inApatosaurus louisae.[3] The femora ofBrontosaurus are very stout and represent some of the most robust femora of any member of Sauropoda. Thetibia andfibula bones are different from the slender bones ofDiplodocus but are nearly indistinguishable from those ofCamarasaurus. The fibula is longer and slenderer than the tibia. The foot ofBrontosaurus has three claws on the innermost digits; the digit formula is 3-4-5-3-2. The first metatarsal is the stoutest, a feature shared among diplodocids.[22]B. excelsus'astragalus differs from other species in that it lacks a laterally directed ventral shelf.[3]
Brontosaurus is a member of thefamily Diplodocidae, aclade of gigantic sauropoddinosaurs. The family includes some of the longest and largest creatures ever to walk the earth, includingDiplodocus,Supersaurus, andBarosaurus. Diplodocids first evolved during theMiddle Jurassic in what is nowGeorgia, spreading toNorth America during the Late Jurassic.[53]Brontosaurus is classified in the subfamily Apatosaurinae, which also includesApatosaurus and possibly one or more unnamed genera.[3] Othniel Charles Marsh describedBrontosaurus as being allied toAtlantosaurus, within the now defunct groupAtlantosauridae.[19][54] In 1878, Marsh raised his family to the rank of suborder, includingApatosaurus,Brontosaurus,Atlantosaurus,Morosaurus (=Camarasaurus), andDiplodocus. He classified this group within Sauropoda. In 1903,Elmer S. Riggs mentioned that the name Sauropoda would be a junior synonym of earlier names, and groupedApatosaurus withinOpisthocoelia.[19] Most authors still use Sauropoda as the group name.[17]
Originally named by its discoverer Othniel Charles Marsh in 1879,Brontosaurus had long been considered ajunior synonym ofApatosaurus; its type species,Brontosaurus excelsus, was reclassified asA. excelsus in 1903. However, an extensive study published in 2015 by a joint British-Portuguese research team concluded thatBrontosaurus was a valid genus of sauropod distinct fromApatosaurus.[3][55][56] Nevertheless, not all paleontologists agree with this division.[57][33] The same study classified two additional species that had once been consideredApatosaurus andEobrontosaurus asBrontosaurus parvus andBrontosaurus yahnahpin respectively.[3]
Cladogram of the Diplodocidae after Tschopp,Mateus, and Benson (2015):[3]
| Diplodocidae |
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Thecladogram below is the result of an analysis by Tschopp, Mateus, and Benson (2015). The authors analyzed most diplodocid type specimens separately to deduce which specimen belonged to which species and genus.[3]
| Apatosaurinae |
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WhenBrontosaurus was described in 1879, the widespread notion in the scientific community was that sauropods weresemi-aquatic, lethargic reptiles that were inactive.[62][4][8] In Othniel Marsh's publicationThe Dinosaurs of North America, he described the dinosaur as "more or less amphibious, and its food was probably aquatic plants or other succulent vegetation".[8] This is unsupported by fossil evidence. Instead, sauropods were active and had adaptations for dwelling on land.[28] Marsh also noted the animal's supposed lack of intellect based on the smallbraincase of the Felch Quarry skull and slenderneural cord. Recent research has found signs of intelligence in dinosaurs, akin to modern birds, though sauropods had relatively small brains.[63]
Various uses for the single claw on the forelimb of sauropods have been proposed. One suggestion is that they were used for defense, but their shape and size make this unlikely. It was also possible they were for foraging, but the most probable use for the claw was grasping objects such as tree trunks when rearing.[52]
Trackways of sauropods likeBrontosaurus show that the average range for them was around 20–40 km (10–25 mi) per day, and they could potentially reach a top speed of 20–30 km/h (12–19 mph).[64] The slow locomotion of sauropods may be due to the minimal muscling or recoil after strides.[65] A possible bipedal trackway of a juvenileApatosaurus is known, but it is disputed if it was possible for the sauropod.[66]
Being a diplodocid sauropod,Brontosaurus was herbivorous and fed onferns,cycadeoids,seed ferns, andhorsetails, eating at ground height as anonselective browser.[38] The replacement method and physiology ofApatosaurus' teeth is unique, with the entire tooth row being replaced at once and up to 60% more often thanDiplodocus. The teeth ofApatosaurus are thick, lack denticles, and are strongly cylindrical in cross-section whereas they are long, slender, and elliptical in cross-section inDiplodocus. These characteristics imply thatApatosaurus, and likelyBrontosaurus, consumed tougher vegetation thanDiplodocus.[25] Diplodocids in general also have shorter necks than the long-necked, vertically inclined macronarians. This would result inniche partitioning, the various taxa thus avoiding direct competition with each other due to feeding on different plants and at different heights.[67] Hypotheses of the food requirements ofBrontosaurus have been made, though predicting this is difficult due to the lack of modern analogues.[68]Endotherms (mammals) andectotherms (reptiles) require a specific amount ofnutrition to survive which correlates with theirmetabolism as well as body size. Estimations of the dietary necessities ofBrontosaurus were made in 2010, with a guess of 2•10^4 to 50•10^4kilojoules needed daily. This led to hypotheses on the distributions ofBrontosaurus to meet this requirement, though they varied on whether it was an ectotherm or endotherm. IfBrontosaurus was an endotherm, fewer adult individuals could be sustained than if it were an ectotherm, which could have tens of animals per square kilometer.[69][70] Due to this, it has been theorized thatBrontosaurus and other sauropods living within the arid environment of the Morrison Formation participated in migrations between feeding sites.[68] James Farlow (1987) calculates that aBrontosaurus-sized dinosaur about 35 t (34 long tons; 39 short tons) would have possessed 5.7 t (5.6 long tons; 6.3 short tons) of fermentation contents.[71] AssumingApatosaurus had an avian respiratory system and a reptilian resting-metabolism, Frank Paladinoet al. (1997) estimate the animal would have needed to consume only about 262 liters (58 imp gal; 69 U.S. gal) of water per day.[72]
Historically, sauropods likeBrontosaurus were believed to have been too massive to support their weight on dry land, so theoretically, they must have lived partly submerged in water, perhaps in swamps. Recent findings do not support this, and sauropods are thought to have been fully terrestrial animals.[73] Diplodocids likeBrontosaurus are often portrayed with their necks held high up in the air, allowing them to browse on tall trees. Though some studies have suggested that diplodocid necks were less flexible than previously believed,[74] other studies have found that alltetrapods appear to hold their necks at the maximum possible vertical extension when in a normal, alert posture, and argue that the same would hold true for sauropods barring any unknown, unique characteristics that set the soft tissue anatomy of their necks apart from that of other animals.[75]
James Spotilaet al. (1991) suggest that the large body size ofBrontosaurus and other sauropods would have made them unable to maintain high metabolic rates, as they would not be able to release enough heat. However, temperatures in the Jurassic were 3 degrees Celsius higher than present.[76] Furthermore, they assumed that the animals had a reptilian respiratory system. Matt Wedel found that an avian system would have allowed them to dump more heat.[77] Some scientists have also argued that the heart would have had trouble sustaining sufficient blood pressure to oxygenate the brain.[73]
Given the large body mass and long neck of sauropods likeBrontosaurus, physiologists have encountered problems determining how these animals breathed. Beginning with the assumption that, likecrocodilians,Brontosaurus did not have adiaphragm, thedead-space volume (the amount of unused air remaining in the mouth, trachea, and air tubes after each breath) has been estimated at 0.184 m3 (184 L) for a 30 t (30 long tons; 33 short tons) specimen. Paladino calculates itstidal volume (the amount of air moved in or out during a single breath) at 0.904 m3 (904 L) with an avian respiratory system, 0.225 m3 (225 L) if mammalian, and 0.019 m3 (19 L) if reptilian.[72]
Based on this, its respiratory system would likely have consisted ofparabronchi, with multiple pulmonary air sacs as inavian lungs, and a flow-through lung. An avian respiratory system would need a lung volume of about 0.60 m3 (600 L) compared with a mammalian requirement of 2.95 m3 (2,950 L), which would exceed the space available. The overall thoracic volume of the same-sizedApatosaurus has been estimated at 1.7 m3 (1,700 L), allowing for a 0.50 m3 (500 L), four-chambered heart and a 0.90 m3 (900 L) lung capacity. That would allow about 0.30 m3 (300 L) for the necessary tissue.[72] Evidence for the avian system inBrontosaurus and other sauropods is also present in the pneumaticity of the vertebrae. Though this plays a role in reducing the weight of the animal, Wedel (2003) states they are also likely connected to air sacs, as in birds.[77]
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A 1999 microscopic study ofApatosaurus andBrontosaurus bones concluded the animals grew rapidly when young and reached near-adult sizes in about 10 years.[78] In 2008, a study on the growth rates of sauropods was published by biologists Thomas Lehman andHolly Woodward. They said that by using growth lines and length-to-mass ratios,Apatosaurus would have grown to 25 t (25 long tons; 28 short tons) in 15 years, with growth peaking at 5,000 kg (11,000 lb) in a single year. An alternative method, using limb length and body mass, foundBrontosaurus andApatosaurus grew 520 kg (1,150 lb) per year, and reached their full mass before it was about 70 years old.[79] These estimates have been called unreliable because the calculation methods are not sound; old growth lines would have been obliterated by bone remodeling.[80] One of the first identified growth factors ofApatosaurus was the number of sacral vertebrae, which increased to five by the time of the creature's maturity. This was first noted in 1903 and again in 1936.[22][19]
JuvenileBrontosaurus material is known based on the type specimen ofB. parvus. The material of this specimen, CM 566, includes vertebrae from various regions, one pelvic bone, and some bones of the hindlimb.[17] When describingB. parvus, Peterson and Gilmore noted that the neural spines were sutured, the sacral vertebrae were unfused, and the coracoid was missing. All of these features are signs of immaturity in other archosaurs, showing that sauropods had these traits too.[15] Peterson and Gilmore also theorized that sauropods never stopped growing, which supposedly helped in attaining their massive size, a concept unsupported by fossils.[81]
An article that appeared in the November 1997 issue ofDiscover magazine reported research into the mechanics of diplodocid tails byNathan Myhrvold, acomputer scientist fromMicrosoft. Myhrvold carried out acomputer simulation of the tail, which in diplodocids likeBrontosaurus was a very long, tapering structure resembling abullwhip. This computer modeling suggested that sauropods were capable of producing a whip-like cracking sound of over 200decibels, comparable to the volume of acannon.[82] There is some circumstantial evidence supporting this as well: a number of diplodocids have been found with fused or damaged tail vertebrae, which may be a symptom of cracking their tails: these are particularly common between the 18th and the 25th caudal vertebra, a region the authors consider a transitional zone between the stiff muscular base and the flexible whiplike section.[83] However, Rega (2012) notes thatCamarasaurus while lacking a tailwhip, displays a similar level of caudal co-ossification and thatMamenchisaurus while having the same pattern of vertebral metrics, lacks a tailwhip and does not display fusion in any "transitional region". Also, the crush fractures which would be expected if the tail was used as a whip have never been found in diplodocids.[84] More recently, Baron (2020) has considered the use of the tail as a bullwhip unlikely because of the potentially catastrophic muscle and skeletal damage such speeds could cause on the large and heavy tail. Instead, he proposes that the tails might have been used as a tactile organ to keep in touch with the individuals behind and to the sides of the animal in a group, which could have augmented cohesion and allowed communication among individuals while limiting more energetically demanding activities like stopping to search for dispersed individuals, turning to visually check on others behind, or communicating vocally.[85]
The cervical vertebrae ofBrontosaurus andApatosaurus are robust, which has led to speculation on the use of these structures. These structures had expensive energy requirements, so the reason for their evolution must have been important to the animal. Notable features include dense cervical ribs and diapophyses, ribs that are angled ventrally, and an overall subtriangular cross-section. These traits are in contrast to the more fragile cervicals of diplodocines.[86] Cervical ribs acted as anchors for thelongus colli ventralis andflexer colli lateralis muscles, which are used in the downward motion of the neck. Stronger muscles for ventral motions allowed more force to be exerted downward. The cervical ribs formed a "V"-shape, which could be used to shelter the softer underlying tissues of the neck from damage. Ventral sides of the cervical ribs were capped by round, protrudingprocesses. These have been suggested to have been attachment points forbosses orkeratinous spikes. Apreprint by Wedelet al (2015) thought that due to the combination of these traits,Brontosaurus would use its neck for combat between individuals through the use of striking necks.[42][87] Behavior like this has been observed in other animals like giraffes and large tortoises.[88][89]
The Morrison Formation is a sequence of shallow marine and alluvial sediments which, according toradiometric dating, ranges between 156.3 million years old (Mya) at its base,[90] and 146.8 Mya at the top,[91] which places it in the lateOxfordian, Kimmeridgian, and early Tithonianstages of the Late Jurassic period. This formation is interpreted as asemi-arid environment with distinctwet anddry seasons. The Morrison Basin, where dinosaurs lived, stretched from New Mexico to Alberta and Saskatchewan and was formed when the precursors to theFront Range of the Rocky Mountains started pushing up to the west. The deposits from their east-facingdrainage basins were carried by streams andrivers and deposited inswampy lowlands, lakes, river channels, andfloodplains.[92] This formation is similar in age to theLourinhã Formation inPortugal and theTendaguru Formation inTanzania.[93]
Brontosaurus may have been a more solitary animal than other Morrison Formation dinosaurs.[94] As a genus,Brontosaurus existed for a long interval, and was found in most levels of the Morrison.B. excelsus fossils have been reported from only the Brushy Basin Member, dating to the late Kimmeridgian age, about 151 Mya.[59] OlderBrontosaurus remains have also been identified from the middle Kimmeridgian, and are assigned toB. parvus.[17] Fossils of these animals have been found inNine Mile Quarry andBone Cabin Quarry in Wyoming and at sites in Colorado, Oklahoma, and Utah, present in stratigraphic zones 2–6 according to John Foster’s model.[95]
The Morrison Formation records an environment and time dominated by gigantic sauropod dinosaurs.[95] Dinosaurs known from the Morrison include the theropodsCeratosaurus,Ornitholestes, andAllosaurus, the sauropodsApatosaurus,Brachiosaurus,Camarasaurus, andDiplodocus, and theornithischiansCamptosaurus,Dryosaurus, andStegosaurus.[96] Other vertebrates that shared this paleoenvironment includedray-finned fishes,frogs,salamanders,turtles,sphenodonts,lizards, terrestrial and aquaticcrocodylomorphs, and several species ofpterosaurs. Shells ofbivalves and aquaticsnails, are also common. The flora of the period has been revealed by fossils ofgreen algae,mosses,horsetails,cycads,ginkgoes, and several families ofconifers. Vegetation varied from river-lining forests oftree ferns and ferns (gallery forests), to fernsavannas with occasional trees such as theAraucaria-like coniferBrachyphyllum.[97]
The length of time taken for Riggs's 1903 reclassification ofBrontosaurus asApatosaurus to be brought to public notice, as well as Osborn's insistence that theBrontosaurus name be retained despite Riggs's paper, meant thatBrontosaurus became one of the most famous dinosaurs.Brontosaurus has often been depicted in cinema, beginning withWinsor McCay's 1914 classicGertie the Dinosaur, one of the first animated films.[98] McCay based his unidentified dinosaur on the apatosaurine skeleton in the American Museum of Natural History.[99] The 1925 silent filmThe Lost World featured a battle between aBrontosaurus and anAllosaurus, usingspecial effects byWillis O'Brien.[100] The 1933 filmKing Kong featured aBrontosaurus chasing Carl Denham, Jack Driscoll and the terrified sailors on Skull Island. In 1938 the assembling of aBrontosaurus skeleton was a major plot point in theKatharine Hepburn andCary Grant filmBringing Up Baby. These, and other early uses of the animal as a major representative of the group, helped cementBrontosaurus as a quintessential dinosaur in the public consciousness.[101]
Sinclair Oil Corporation has long been a fixture of American roads (and briefly in other countries) with its green dinosaur logo and mascot, aBrontosaurus. While Sinclair's early advertising included a number of different dinosaurs, eventually onlyBrontosaurus was used as the official logo, due to its popular appeal.[102]
As late as 1989, theU.S. Postal Service faced controversy when it issued four "dinosaur" stamps:Tyrannosaurus,Stegosaurus,Pteranodon, andBrontosaurus. The use of the termBrontosaurus in place ofApatosaurus led to complaints of "fostering scientific illiteracy."[103] The Postal Service defended itself (in Postal Bulletin 21742)[104] by saying, "Although now recognized by the scientific community asApatosaurus, the nameBrontosaurus was used for the stamp because it is more familiar to the general population." Indeed, the Postal Service even implicitly rebuked the somewhat inconsistent complaints by adding that "[s]imilarly, the term 'dinosaur' has been used generically to describe all the animals [i.e., all four of the animals represented in the given stamp set], even though thePteranodon was a flying reptile [rather than a true 'dinosaur']," a distinction left unmentioned in the numerous correspondence regarding theBrontosaurus/Apatosaurus issue.[105] PalaeontologistStephen Jay Gould supported this position. In the essay from which the title of the 1991 collectionBully for Brontosaurus is taken, Gould wrote: "Touché and right on; no one bitched aboutPteranodon, and that's a real error."[101] His position, however, was not one suggesting the exclusive use of the popular name; he echoed Riggs' original argument thatBrontosaurus is a synonym forApatosaurus. Nevertheless, he noted that the former has developed and continues to maintain an independent existence in the popular imagination.[101]
The more vociferous denunciations of the usage have elicited sharply defensive statements from those who would not wish to see the name be struck from official usage.[101] Tschopp's study[3] has generated a very high number of responses from many, often opposed,groups — of editorial,[106] news staff,[55][107] and personal blog nature (both related[108][109] and not[110]), from both[111] sides of the debate, from related[18] and unrelated contexts, and from all over the world.[112]
Since Wedelet al's 2015 preprint,[42] various reconstructions ofBrontosaurus individuals engaging in intraspecific combat based on their study have been made. The art typically depicts the neck-battling hypothesis stipulated by their research. Many of these works are published online under the hashtag "#BrontoSmash".[113][114]
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