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Diplodocus

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Not to be confused withDiplocaulusorDiplococcus.

Diplodocus
Temporal range:Late Jurassic(Kimmeridgian),154–152Ma
↓
MountedD. carnegii(or "Dippy") skeleton at theCarnegie Museum of Natural History;considered the most famous single dinosaur skeleton in the world.[1][2]
Scientific classificationEdit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Saurischia
Clade: †Sauropodomorpha
Clade: †Sauropoda
Superfamily: †Diplodocoidea
Family: †Diplodocidae
Subfamily: †Diplodocinae
Genus: †Diplodocus
Marsh,1878
Type species
†Diplodocus longus
(nomen dubium)
Marsh,1878
Other species
  • †D. carnegii
    Hatcher,1901
  • †D. hallorum
    (Gillette,1991) (originallySeismosaurus)
Synonyms
  • Seismosaurus
    Gillette, 1991

Diplodocus(/dɪˈplɒdəkəs/,[3][4]/daɪˈplɒdəkəs/,[4]or/ˌdɪploʊˈdoʊkəs/[3]) was agenusofdiplodocidsauropoddinosaurs,whosefossilswere first discovered in 1877 byS. W. Williston.The generic name, coined byOthniel Charles Marshin 1878, is aNeo-Latinterm derived fromGreekδιπλός (diplos) "double" and δοκός (dokos) "beam",[3][5]in reference to the double-beamedchevron boneslocated in the underside of the tail, which were then considered unique.

The genus of dinosaurs lived in what is now mid-western North America, at the end of theJurassicperiod.It is one of the more common dinosaur fossils found in the middle to upperMorrison Formation,between about 154 and 152 million years ago, during the lateKimmeridgian Age.[6]The Morrison Formation records an environment and time dominated by gigantic sauropod dinosaurs, such asApatosaurus,Barosaurus,Brachiosaurus,Brontosaurus,andCamarasaurus.[7]Its great size may have been a deterrent to the predatorsAllosaurusandCeratosaurus:their remains have been found in the samestrata,which suggests that they coexisted withDiplodocus.

Diplodocusis among the most easily identifiable dinosaurs, with its typical sauropod shape, long neck and tail, and four sturdy legs. For many years, it was the longest dinosaur known.

Description[edit]

Sizes ofDiplodocus carnegii(orange) andD. hallorum(green) compared with a human.

Among the best-known sauropods,Diplodocuswere very large, long-necked,quadrupedalanimals, 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 withcantilever bridges.[8]In fact,D. carnegiiis currently one of the longest dinosaurs known from a complete skeleton,[8]with a total length of 24–26 meters (79–85 ft).[9][10]Modern mass estimates forD. carnegiihave tended to be in the 12–14.8-metric-ton (13.2–16.3-short-ton) range.[9][11][10]

Diplodocus hallorum,known from partial remains, was even larger, and is estimated to have been the size of fourelephants.[12]When first described in 1991, discovererDavid Gillettecalculated it to be 33 m (110 ft) long based on isometric scaling withD. carnegii.However, he later stated that this was unlikely and estimated it to be 39 – 45 meters (130 – 150 ft) long, suggesting that some individuals may have been up to 52 m (171 ft) long and weighed 80 to 100 metric tons,[13]making it the longest known dinosaur (excluding those known from exceedingly poor remains, such asAmphicoeliasorMaraapunisaurus). The estimated length was later revised downward to 30.5–35 m (100–115 ft) and later on to 29–33.5 m (95–110 ft)[14][15][16][10][9]based on findings that show that Gillette had originally misplaced vertebrae 12–19 as vertebrae 20–27. Weight estimates based on the revised length are as high as 38 metric tons (42 short tons)[14]although more recently, and according to Gregory S. Paul, a 29 m (95 ft) longD. hallorumwas estimated to weigh 23 metric tons (25 short tons) in body mass.[9]The nearly completeD. carnegiiskeleton at theCarnegie Museum of Natural HistoryinPittsburgh, Pennsylvania,on which size estimates ofD. hallorumare mainly based, also was found to have had its 13th tail vertebra come from another dinosaur, throwing off size estimates forD. hallorumeven further. While dinosaurs such asSupersauruswere probably longer, fossil remains of these animals are only fragmentary andD. hallorumstill remains among the longest known dinosaurs.[14][17]

Caudal vertebrae ofD. carnegiishowing the double-beamed chevron bones to which the genus name refers,Natural History Museum, London

Diplodocushad an extremely long tail, composed of about 80caudal vertebrae,[18]which are almost double the number some of the earlier sauropods had in their tails (such asShunosauruswith 43), and far more than contemporaneousmacronarianshad (such asCamarasauruswith 53). Some speculation exists as to whether it may have had a defensive[19]or noisemaking (by cracking it like acoachwhip)[20]or, as more recently suggested, tactile function.[21]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 gaveDiplodocusits 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 toDiplodocus;since then they have been discovered in other members of thediplodocidfamily as well as in non-diplodocid sauropods, such asMamenchisaurus.[22]

Reconstruction ofD. carnegiiwith horizontal neck, flexible whip tail, keratinous spines and nostrils low on the snout

Like other sauropods, the manus (front "feet" ) ofDiplodocuswere highly modified, with the finger and hand bones arranged into a vertical column,horseshoe-shapedin cross section.Diplodocuslacked 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.[23]

No skull has ever been found that can be confidently said to belong toDiplodocus,though skulls of other diplodocids closely related toDiplodocus(such asGaleamopus) are well known. The skulls of diplodocids were very small compared with thesizeof these animals.Diplodocushad small, 'peg'-like teeth that pointed forward and were only present in theanteriorsections of the jaws.[24]Its braincase was small, and the neck was composed of at least 15vertebrae.[25]

Diplodocussp. scale shapes. These scale shapes include (1) rectangular, (2) ovoid and dome, (3) arching scale rows, (4) globular.

Skin[edit]

The discovery of partial diplodocid skin impressions in 1990 showed that some species had narrow, pointed,keratinousspines, much like those on aniguana.The spines could be up to 18 centimeters (7.1 in) long, on the "whiplash" portion of their tails, and possibly along the back and neck as well, similarly tohadrosaurids.[26][27]The spines have been incorporated into many recent reconstructions ofDiplodocus,notablyWalking with Dinosaurs.[28]The original description of the spines noted that the specimens in the Howe Quarry nearShell, Wyomingwere associated with skeletal remains of an undescribed diplodocid "resemblingDiplodocusandBarosaurus."[26]Specimens from this quarry have since been referred toKaatedocus siberiandBarosaurussp., rather thanDiplodocus.[6][29]

Fossilized skin ofDiplodocussp., discovered at theMother'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 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 the arching scale rows look similar to the scale orientations seen aroundcrocodilianlimbs, suggesting that this area may have also originated from around a limb on theDiplodocus.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.[30]

Discovery and history[edit]

Bone Wars andDiplodocus longus[edit]

The first record ofDiplodocuscomes from Marshall P. Felch’s quarry atGarden ParknearCañon City,Colorado,when several fossils were collected byBenjamin MudgeandSamuel Wendell Willistonin 1877. The first specimen (YPM VP 1920) was very incomplete, consisting only of two complete caudal vertebrae, a chevron, and several other fragmentary caudal vertebrae. The specimen was sent to theYale Peabody Museumand was namedDiplodocus longus('long double-beam') bypaleontologistOthniel Charles Marshin 1878.[31]Marsh namedDiplodocusduring theBone Wars,his competition with Philadelphian paleontologistEdward Drinker Copeto collect and describe as many fossil taxa as possible.[32]Though several more complete specimens have been attributed toD. longus,[33][34]detailed analysis has discovered that this type specimen is actually dubious, which is not an ideal situation for the type species of a well-known genus likeDiplodocus.A petition to theInternational Commission on Zoological Nomenclaturewas being considered which proposed makingD. carnegiithe new type species.[6][35]This proposal was rejected by the ICZN andD. longushas been maintained as the type species.[36]

Although the type specimen was very fragmentary, several additional diplodocid fossils were collected at Felch’s quarry from 1877 to 1884 and sent to Marsh, who then referred them toD. longus.One specimen (USNMV 2672), an articulated complete skull, mandibles, and partial atlas was collected in 1883, and was the first complete Diplodocid skull to be reported.[37][38]Tschoppet al.’s analysis placed it as an indeterminate diplodocine in 2015 due to the lack of overlap with any diagnosticDiplodocuspostcranial material, as was the fate with all skulls assigned toDiplodocus.[6]

Second Dinosaur Rush andDiplodocus carnegii[edit]

Barnum Brown (left) and Henry Osborn (right) excavating a femur ofDiplodocus hallorum(AMNH 223), 1897.
Several elements referred toDiplodocus longus,including atypecaudal at the bottom, as figured in Marsh, 1896.[39]

After the end of the Bone Wars, many major institutions in the eastern United States were inspired by the depictions and finds by Marsh and Cope to assemble their own dinosaur fossil collections.[32]The competition to mount the first sauropod skeleton specifically was the most intense, with theAmerican Museum of Natural History,Carnegie Museum of Natural History,andField Museum of Natural Historyall sending expeditions to the west to find the most complete sauropod specimen, bring it back to the home institution, and mount it in their fossil halls.[32]The American Museum of Natural History was the first to launch an expedition, finding a semi-articulated partial postcranial skeleton containing many vertebrae ofDiplodocusin atComo Bluffin 1897. The skeleton (AMNH FR 223) was collected byBarnum BrownandHenry Osborn,who shipped the specimen to the AMNH and it was briefly described in 1899 by Osborn, who referred it toD. longus.It was later mounted—the firstDiplodocusmount made—and was the first well preserved individual skeleton ofDiplodocusdiscovered.[6][33]In Emmanuel Tschoppet al.'s phylogenetic analysis ofDiplodocidae,AMNH FR 223 was found to be not a skeleton ofD. longus,but the later named speciesD. hallorum.[6]

The most notableDiplodocusfind also came in 1899, when crew members from theCarnegie Museum of Natural Historywere collecting fossils in theMorrison FormationofSheep Creek,Wyoming,with funding from Scottish-American steel tycoonAndrew Carnegie,they discovered a massive and well preserved skeleton ofDiplodocus.[40]The skeleton was collected that year by Jacob L. Wortman and several other crewmen under his direction along with several specimens ofStegosaurus,Brontosaurus parvus,andCamarasauruspreserved alongside the skeleton.[40]The skeleton (CM 84) was preserved in semi articulation and was very complete, including 41 well preserved vertebrae from the midcaudalsto the anteriorcervicals,18 ribs, 2 sternal ribs, a partial pelvis, rightscapulocoracoid,and right femur. In 1900, Carnegie crews returned to Sheep Creek, this expedition led byJohn Bell Hatcher,William Jacob Holland,andCharles Gilmore,and discovered another well preserved skeleton ofDiplodocusadjacent to the specimen collected in 1899.[6][40]The second skeleton (CM 94) was from a smaller individual and had preserved fewer vertebrae, but preserved more caudal vertebrae and appendicular remains than CM 84.[40][6]Both of the skeletons were named and described in great detail by John Bell Hatcher in 1901, with Hatcher making CM 84 the type specimen of a new species ofDiplodocus,Diplodocus carnegii( "Andrew Carnegie's double beam "),[6][40]with CM 94 becoming the paratype.[40]

It wasn't until 1907, that the Carnegie Museum of Natural History created a composite mount ofDiplodocus carnegiithat incorporated CM 84 and CM 94 along with several other specimens and even other taxa were used to complete the mount, including a skull molded based on USNM 2673, a skull assigned toGaleamopus pabsti.[41][6]The Carnegie Museum mount became very popular, being nicknamed "Dippy"by the populace, eventually being cast and sent to museums inLondon,Berlin,Paris,Vienna,Bologna,St. Petersburg,Buenos Aires,Madrid,andMexico Cityfrom 1905 to 1928.[42]TheLondon castspecifically became very popular; its casting was requested byKing Edward VIIand it was the first sauropod mount put on display outside of the United States.[42]The goal of Carnegie in sending these casts overseas was apparently to bring international unity and mutual interest around the discovery of the dinosaur.[43]

Dinosaur National Monument[edit]

The Carnegie Museum of Natural History made another landmark discovery in 1909 whenEarl Douglassunearthed several caudal vertebrae fromApatosaurusin what is nowDinosaur National Monumenton the border region between Colorado and Utah, with the sandstone dating to theKimmeridgianof theMorrison Formation.From 1909 to 1922, with the Carnegie Museum excavating the quarry, eventually unearthing over 120 dinosaur individuals and 1,600+ bones, many of the associated skeletons being very complete and are on display in several American museums. In 1912, Douglass found a semi articulated skull of a diplodocine with mandibles (CM 11161) in the Monument. Another skull (CM 3452) was found by Carnegie crews in 1915, bearing 6 articulated cervical vertebrae and mandibles, and another skull with mandibles (CM 1155) was found in 1923. All of the skulls found at Dinosaur National Monument were shipped back to Pittsburgh and described byWilliam Jacob Hollandin detail in 1924, who referred the specimens toD. longus.[44]This assignment was also questioned by Tschopp, who stated that all of the aforementioned skulls could not be referred to any specific diplodocine. Hundreds of assorted postcranial elements were found in the Monument that have been referred toDiplodocus,but few have been properly described.[6]A nearly complete skull of a juvenileDiplodocuswas collected by Douglass in 1921, and it is the first known from aDiplodocus.[45]

AnotherDiplodocusskeleton was collected at the Carnegie Quarry in Dinosaur National Monument, Utah, by theNational Museum of Natural Historyin 1923. The skeleton (USNM V 10865) is one of the most complete known fromDiplodocus,consisting of a semi-articulated partial postcranial skeleton, including a well preserved dorsal column. The skeleton was briefly described byCharles Gilmorein 1932, who also referred it toD. longus,and it was mounted in the fossil hall at the National Museum of Natural History the same year. In Emmanuel Tschoppet al.'s phylogenetic analysis of Diplodocidae, USNM V 10865 was also found to be an individual ofD. hallorum.[6][46]

Hatcher's original composite skeletal reconstruction ofDiplodocus carnegii,1901.

TheDenver Museum of Nature and Sciencealso collected aDiplodocusspecimen in Dinosaur National Monument, a partial postcranial skeleton including cervical vertebrae, that was later mounted in the museum. Although not described in detail, Tschopp and colleagues determined that this skeleton also belonged toD. hallorum.[6]

Recent discoveries andDiplodocus hallorum[edit]

FewDiplodocusfinds came for many years until 1979, when three hikers came across several vertebrae stuck in elevated stone next to severalpetroglyphsin a canyon west ofSan Ysidro,New Mexico.The find was reported to theNew Mexican Museum of Natural History,who dispatched an expedition led byDavid D. Gillettein 1985, that collected the specimen after several visits from 1985 to 1990. The specimen was preserved in semi-articulation, including 230gastroliths,with several vertebrae, partial pelvis, and right femur and was prepared and deposited at the New Mexican Museum of Natural History under NMMNH P-3690. The specimen was not described until 1991 in theJournal of Paleontology,where Gillette named itSeismosaurus halli(Jim and Ruth Hall's seismic lizard),though in 1994, Gillette published an amendment changing the name toS. hallorum.[13][47]In 2004 and later 2006,Seismosauruswas synonymized withDiplodocusand even suggested to be synonymous with the dubiousD. longusand later Tschoppet al.'s phylogenetic analysis in 2015 supported the idea that many specimens referred toD. longusactually belonged toD. hallorum.[6]

In 1994, theMuseum of the Rockiesdiscovered a very productive fossil site atMother's Day QuarryinCarbon County, Montanafrom the Salt Wash member of theMorrison Formationthat was later excavated by theCincinnati Museum of Natural History and Sciencein 1996, and after that theBighorn Basin Paleontological Institutein 2017. The quarry was very productive, having mostly isolatedDiplodocusbones from juveniles to adults in pristine preservation. The quarry notably had a great disparity between the amount of juveniles and adults in the quarry, as well as the frequent preservation of skin impressions,pathologies,and some articulated specimens fromDiplodocus.[47][30]One specimen, a nearly complete skull of a juvenileDiplodocus,was found at the quarry and is one of few known and highlighted ontogenetic dietary changes in the genus.[48]

Classification and species[edit]

Phylogeny[edit]

Diplodocusis both thetype genusof, and gives its name to, the Diplodocidae, the family in which it belongs.[37]Members of this family, while still massive, have a markedly more slender build than other sauropods, such as thetitanosaursandbrachiosaurs.All are characterized by long necks and tails and a horizontal posture, with forelimbs shorter than hind limbs. Diplodocids flourished in the Late Jurassic of North America and possibly Africa.[18]

A subfamily, theDiplodocinae,was erected to includeDiplodocusand its closest relatives, includingBarosaurus.More distantly related is the contemporaneousApatosaurus,which is still considered a diplodocid, although not a diplodocine, as it is a member of the sister subfamilyApatosaurinae.[49][50]The PortugueseDinheirosaurusand the AfricanTornieriahave also been identified as close relatives ofDiplodocusby some authors.[51][52]Diplodocoideacomprises the diplodocids, as well as thedicraeosaurids,rebbachisaurids,Suuwassea,[49][50]Amphicoelias[52]possiblyHaplocanthosaurus,[53]and/or thenemegtosaurids.[54]Thecladeis the sister group toMacronaria(camarasaurids,brachiosauridsand titanosaurians).[53][54]

Acladogramof the Diplodocidae after Tschopp, Mateus, and Benson (2015) below:[6]

Diplodocussp. skeleton nicknamed "Misty",Zoological Museum of Copenhagen
Diplodocidae

Valid species[edit]

  • Diplodocus carnegii(also spelledD. carnegiei), named afterAndrew Carnegie,is the best known, mainly due to a near-complete skeleton known asDippy(specimen CM 84) collected by Jacob Wortman, of theCarnegie Museum of Natural HistoryinPittsburgh, Pennsylvania,and described and named byJohn Bell Hatcherin 1901.[55]It was reconsidered as thetype speciesforDiplodocus.[35]
  • Diplodocus hallorum,first described in 1991 by Gillette asSeismosaurus hallifrom a partial skeleton comprising vertebrae, pelvis and ribs (specimen NMMNH P-3690).[56]As the specific name honors two people, Jim and Ruth Hall (ofGhost Ranch[57]),George Olshevskylater suggested to emend the name asS. hallorum,using the mandatorygenitiveplural; Gillette then emended the name,[13]which usage has been followed by others, including Carpenter (2006).[14]In 2004, a presentation at the annual conference of theGeological Society of Americamade a case forSeismosaurusbeing ajunior synonymofDiplodocus.[58]This was followed by a much more detailed publication in 2006, which not only renamed the speciesDiplodocus hallorum,but also speculated that it could prove to be the same asD. longus.[59]The position thatD. hallorumshould be regarded as a specimen ofD. longuswas also taken by the authors of a redescription ofSupersaurus,refuting a previous hypothesis thatSeismosaurusandSupersauruswere the same.[60]A 2015 analysis of diplodocid relationships noted that these opinions are based on the more complete referred specimens ofDiplodocus longus.The authors of this analysis concluded that those specimens were indeed the same species asD. hallorum,but thatD. longusitself was anomen dubium.[6]
    Skeletal reconstruction ofD. carnegiispecimens CM 84 and CM 94, with missing portions reconstructed after other diplodocids

Nomina dubia(doubtful species)[edit]

USNM 2672, a skull formerly thought to have belonged to theholotypeofD. longus
  • Diplodocus 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 toD. longus,[34]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 anomen dubium,which Tschopp et al. regarded as not an ideal situation for the type species of a well-known genus likeDiplodocus.A petition to theInternational Commission on Zoological Nomenclature(ICZN) was being considered, which proposed to makeD. carnegiithe new type species.[6][35]The proposal was rejected by the ICZN andD. longushas been maintained as the type species.[36]However, in comments responding to the petition, some authors regardedD. longusas potentially valid after all.[61][62]
  • Diplodocus lacustris( "of the lake" ) is anomen dubiumnamed by Marsh in 1884 based on specimen YPM 1922 found byArthur Lakes,consisting of the snout and upper jaw of a smaller animal fromMorrison, Colorado.[37]The remains are now believed to have been from an immature animal, rather than from a separate species.[63]Mossbruckeret al., 2013 surmised that the dentary and teeth ofDiplodocus lacustriswas actually fromApatosaurus ajax.[64]Later in 2015, it was concluded that the snout of the specimen actually belonged toCamarasaurus.[6]

Formerly assigned species[edit]

  • Diplodocus hayiwas named byWilliam Jacob Hollandin 1924 based on a braincase and partial postcranial skeleton (HMNS175), including a nearly complete vertebral column, found in the Morrison Formation strata nearSheridan, Wyoming.[6][44]D. hayiremained a species ofDiplodocusuntil reassessment by Emmanuel Tschopp and colleagues determined that it was its own genus,Galeamopus,in 2015. The reassessment also found that the skulls AMNH 969 and USNM 2673 were notDiplodocuseither and actually referred specimens ofGaleamopus.[6]

Paleobiology[edit]

Restoration ofD. hallorumin environment

Due to a wealth of skeletal remains,Diplodocusis one of the best-studied dinosaurs. Many aspects of its lifestyle have been subjects of various theories over the years.[22]Comparisons between thescleral ringsof diplodocines and modern birds and reptiles suggest that they may have beencathemeral,active throughout the day at short intervals.[65]

Marsh and then Hatcher[40]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 asBrachiosaurusandApatosaurus.A 1951 study byKenneth A. Kermackindicates 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.[66]Since the 1970s, general consensus has the sauropods as firmly terrestrial animals, browsing on trees, ferns, and bushes.[67]

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 ofdead space.They likely had anavian respiratory system,which is more efficient than amammalianand reptilian system. Reconstructions of the neck and thorax ofDiplodocusshow greatpneumaticity,which could have played a role in respiration as it does in birds.[68]

Posture[edit]

Further information:Sauropod neck posture
An outmoded depiction by Oliver P. Hay (1910), with sprawled limbs[69]

The depiction ofDiplodocusposture has changed considerably over the years. For instance, a classic 1910 reconstruction byOliver P. Haydepicts twoDiplodocuswith splayed lizard-like limbs on the banks of a river. Hay argued thatDiplodocushad a sprawling, lizard-like gait with widely splayed legs,[70]and was supported byGustav Tornier.This hypothesis was contested byWilliam Jacob Holland,who demonstrated that a sprawlingDiplodocuswould have needed a trench through which to pull its belly.[71]Finds of sauropod footprints in the 1930s eventually put Hay's theory to rest.[67]

Upright neck pose forD. carnegiibased on Tayloret al.(2009)
A reconstruction of the neck ligament structure from a Diplodocus. The depiction of the entire neck seen in C and D shows where the possible elastic and supraspinal ligaments in addition to muscle groups could have been located.[72]

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 ofDiplodocusneck was close to horizontal, rather than vertical, and scientists such as Kent Stevens have used this to argue that sauropods includingDiplodocusdid not raise their heads much above shoulder level.[73][74]Anuchal ligamentmay have held the neck in this position.[73]One approach to understanding the possible ligament structure in ancient sauropods is to study the ligaments and their attachments to bones in extant animals to see if they resemble any bony structures in sauropods or other dinosaur species likeParasaurolophus.[75]If diplodocus relied on a mammal-like nuchal ligament, it would have been for passively sustaining the weight of its head and neck. This ligament is found in many hoofed mammals, such as bison and horses. In mammals, it typically consists of a funiculus cord that runs from the external occipital crest of the skull to elongate vertebral neural spines or “withers” in the shoulder region plus sheet-like extensions called laminae run from the cord to the neural spines on some or all of the cervical vertebrae. However, most sauropods do not have withers in the shoulders, so if they possessed a similar ligament, it would differ substantially, perhaps anchoring in the hip region.[76][77]Another hypothesized neck-supporting ligament is an avian-like elastic ligament, such as that seen inStruthio camelus.[78][79]This ligament acts similarly to the mammal-like nuchal ligament but comprises short segments of ligament that connect the bases of the neural spines, and therefore does not need a robust attachment zone like those seen in mammals. A 2009 study found that alltetrapodsappear 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 thatDiplodocuswould have held its neck at a more elevated angle than previous studies have concluded.[80]

As with the related genusBarosaurus,the very long neck ofDiplodocusis the source of much controversy among scientists. A 1992Columbia Universitystudy 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".[8]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.[25]

Diet and feeding[edit]

Cast of a diplodocid skull that may belong to a species ofDiplodocus(CM 11161)

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.[24]This implies that the feeding mechanism ofDiplodocusand other diplodocids was radically different from that of other sauropods. Unilateral branch stripping is the most likely feeding behavior ofDiplodocus,[81][82][83]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.[24]

Younget al.(2012) used biomechanical modeling 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.[84]Diplodocine teeth were also continually replaced throughout their lives, usually in less than 35 days, as was discovered by Michael D'Emicet 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 asCamarasaurus.This may have better allowed the various species of sauropods to exist without competition.[85]

Diplodocus(dark green) and various sauropods in a tripodal posture; The white dots showing the approximate center of mass, as estimated in studies.

The flexibility ofDiplodocusneck is debated but it should have been able to browse from low levels to about 4 m (13 ft) when on all fours.[25][73]However, studies have shown that thecenter of massofDiplodocuswas very close to thehip socket;[86][87]this means thatDiplodocuscould 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 postureDiplodocuscould potentially increase its feeding height up to about 11 m (36 ft).[87][88]

Cast of teeth of an unknownDiplodocusspecies

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 whetherDiplodocusgrazed 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.[73]Matthew Cobleyet al.(2013) disputed this, finding that large muscles and cartilage would have limited neck movements. They state that the feeding ranges for sauropods likeDiplodocuswere 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.[89][90]The conclusions of Cobleyet al.were disputed in 2013 and 2014 by Mike Taylor, who analyzed the amount and positioning of intervertebral cartilage to determine the flexibility of the neck ofDiplodocusandApatosaurus.Taylor found that the neck ofDiplodocuswas very flexible, and that Cobleyet al.was incorrect, in that flexibility as implied by bones is less than in reality.[91]

In 2010, Whitlocket al.described a juvenile skull at the time referred toDiplodocus(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.[92]

Reproduction and growth[edit]

Restoration of a narrow snouted juvenile (based on the "Andrew" specimenCMCVP14128) feeding alongside broad snouted adults

While the long neck has traditionally been interpreted as a feeding adaptation, it was also suggested[93]that the oversized neck ofDiplodocusand its relatives may have been primarily a sexual display, with any other feeding benefits coming second. A 2011 study refuted this idea in detail.[94]

While no evidence indicatesDiplodocusnesting habits, other sauropods, such as the titanosaurianSaltasaurus,have been associated with nesting sites.[95][96]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.Diplodocusmay have done the same. The documentaryWalking with Dinosaursportrayed a motherDiplodocususing anovipositorto lay eggs, but it was pure speculation on the part of the documentary author.[28]ForDiplodocusand 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.[97]

Based on a number of bonehistologystudies,Diplodocus,along with other sauropods, grew at a very fast rate, reachingsexual maturityat just over a decade, and continuing to grow throughout their lives.[98][99][100]

Paleoecology[edit]

Restoration of twoD. longus

The Morrison Formation is a sequence of shallow marine and alluvial sediments which, according toradiometric dating,ranges between 156.3 million years old (Ma) at its base,[101]and 146.8 million years old at the top,[102]which places it in the lateOxfordian,Kimmeridgian,and earlyTithonianstagesof the Late Jurassic period. This formation is interpreted as asemi-aridenvironment with distinctwetanddry seasons.The Morrison Basin, where many dinosaurs lived, stretched from New Mexico to Alberta and Saskatchewan, and was formed when the precursors to theFront Rangeof theRocky Mountainsstarted pushing up to the west. The deposits from their east-facingdrainage basinswere carried by streams andriversand deposited inswampylowlands, lakes, river channels, andfloodplains.[103]This formation is similar in age to theLourinha FormationinPortugaland theTendaguru FormationinTanzania.[104]

SaurophaganaxandD. hallorum,New Mexico Museum of Natural History and Science

The Morrison Formation records an environment and time dominated by gigantic sauropod dinosaurs.[105]Dinosaurs known from the Morrison include the theropodsCeratosaurus,Koparion,Stokesosaurus,Ornitholestes,AllosaurusandTorvosaurus,the sauropodsBrontosaurus,Apatosaurus,Brachiosaurus,Camarasaurus,and theornithischiansCamptosaurus,Dryosaurus,Othnielia,GargoyleosaurusandStegosaurus.[106]Diplodocusis commonly found at the same sites asApatosaurus,Allosaurus,Camarasaurus,andStegosaurus.[107]Allosaurusaccounted for 70 to 75% of theropod specimens and was at the toptrophic levelof the Morrisonfood web.[108]Many of the dinosaurs of the Morrison Formation are the same genera as those seen in Portuguese rocks of theLourinha Formation(mainlyAllosaurus,Ceratosaurus,Torvosaurus,andStegosaurus), or have a close counterpart (BrachiosaurusandLusotitan;CamptosaurusandDraconyx).[104]Other vertebrates that shared the same paleoenvironment includedray-finned fishes,frogs,salamanders,turtleslikeDorsetochelys,sphenodonts,lizards,terrestrial and aquaticcrocodylomorphssuch asHoplosuchus,and several species ofpterosaurlikeHarpactognathusandMesadactylus.Shells ofbivalvesand aquaticsnailsare also common. The flora of the period wasgreen algae,fungi,mosses,horsetails,cycads,ginkgoes,and several families ofconifers.Vegetation varied from river-lining forests oftree fernsandferns(gallery forests), to fernsavannaswith occasional trees such as theAraucaria-like coniferBrachyphyllum.[14]

Cultural significance[edit]

"Dippy",the first replica ofD. carnegiiat theNatural History Museum
Holland'sD. carnegiicast in theFrench National Museum of Natural History,in Paris, much as it was in 1908
D. carnegiicast in Berlin, Germany, unveiled in 1908

Diplodocushas been a famous and much-depicted dinosaur as it has been on display in more places than any othersauropoddinosaur.[109] 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[110]did much to familiarize it to people worldwide. Casts ofDiplodocusskeletons are still displayed in many museums worldwide, includingD. carnegiiin a number of institutions.[67]

The project, along with its association with 'big science',philanthropism,and capitalism, drew much public attention in Europe. The German satirical weeklyKladderadatschdevoted 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[111]
But even a much older gent
Sees itself forced to wander
He goes by the nameDiplodocus
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.[112]

D. longusis displayed theSenckenberg MuseuminFrankfurt(a skeleton made up of several specimens, donated in 1907 by theAmerican Museum of Natural History), Germany.[113][114]A mounted and more complete skeleton ofD. longusis at the SmithsonianNational Museum of Natural Historyin Washington, DC,[115]while a mounted skeleton ofD. hallorum(formerlySeismosaurus), which may be the same asD. longus,can be found at theNew Mexico Museum of Natural History and Science.[116]

A war machine (landship) from WW1 namedBoirault machinewas designed in 1915, later deemed impractical and hence given a nickname "Diplodocus militaris".[117]

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