The genus 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, with most specimens being found in rocks dated between about 151.88 and 149.1 million years ago,[6][7] during the latestKimmeridgian Age,[8] although it may have made it into the Tithonian,[9] with at least one specimen (AMNH FR 223) being potentially from among the youngest deposits of the formation.[6] The Morrison Formation records an environment and time dominated by gigantic sauropod dinosaurs, such asApatosaurus,Barosaurus,Brachiosaurus,Brontosaurus, andCamarasaurus.[10] Its great size may have been a deterrent to the predatorsAllosaurus andCeratosaurus: their remains have been found in the samestrata, which suggests that they coexisted withDiplodocus.
Diplodocus is 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.
Sizes ofDiplodocus carnegii (orange) andD. hallorum (green) compared with a human (blue)
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 withcantilever bridges.[11] In fact,D. carnegii is currently one of the longest dinosaurs known from a complete skeleton,[11] with a total length of 24–26 meters (79–85 ft).[12][13] Modern mass estimates forD. carnegii have tended to be in the 12–14.8-metric-ton (13.2–16.3-short-ton) range.[12][14][13]
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 thesize of these animals.Diplodocus had small, 'peg'-like teeth that pointed forward and were only present in theanterior sections of the jaws.[15] Its braincase was small, and the neck was composed of at least 15vertebrae.[16]
Reconstruction ofD. carnegii with horizontal neck, flexible whip tail, keratinous spines and nostrils low on the snout
D. hallorum, known from partial remains, was even larger, and is estimated to have been the size of fourelephants.[17] When first described in 1991, discovererDavid Gillette calculated it to be 33 metres (108 feet) long based on isometric scaling withD. carnegii. However, he later stated that this was unlikely and estimated it to be 39–45 meters (128–148 ft) long, suggesting that some individuals may have been up to 52 metres (171 feet) long and weighed 80 to 100 metric tons,[18] making it the longest known dinosaur (excluding those known from exceedingly poor remains, such asAmphicoelias orMaraapunisaurus). 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)[19][20][21][13][12] 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)[19] although more recently, and according to Gregory S. Paul, a 29 m (95 ft) longD. hallorum was estimated to weigh 23 metric tons (25 short tons) in body mass.[12][22] A study in 2024 later found the mass of a 33 m (108 ft)D. hallorum to be only 21 metric tons (23 short tons), though the study suggested this only represents the average adult size and not the above average or maximum body size.[23] The nearly completeD. carnegii skeleton at theCarnegie Museum of Natural History inPittsburgh, Pennsylvania, on which size estimates ofD. hallorum are mainly based, also was found to have had its 13th tail vertebra come from another dinosaur, throwing off size estimates forD. hallorum even further. While dinosaurs such asSupersaurus were probably longer, fossil remains of these animals are only fragmentary andD. hallorum still remains among the longest known dinosaurs.[19][24][23]
Caudal vertebrae ofD. carnegii showing the double-beamed chevron bones to which the genus name refers,Natural History Museum, London
The estimated tail length ofDiplodocus makes up approximately 55% of the total body length, with the tail sometimes hypothesized to be capable of functioning like a very long, taperingbullwhip.[25] This extremely long tail is composed of about 80caudal vertebrae,[26] which are almost double the number some of the earlier sauropods had in their tails (such asShunosaurus with 43), and far more than contemporaneousmacronarians had (such asCamarasaurus with 53). Some speculation exists as to whether it may have had a defensive[27] or noisemaking (by cracking it like acoachwhip)[28] or, as more recently suggested, tactile function.[25] 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 gaveDiplodocus 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 toDiplodocus; since then they have been discovered in other members of thediplodocid family as well as in non-diplodocid sauropods, such asMamenchisaurus.[29]
Like other sauropods, the manus (front "feet") ofDiplodocus 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.[30]
Diplodocus sp. scale shapes. These scale shapes include (1) rectangular, (2) ovoid and dome, (3) arching scale rows, (4) globular.
The discovery of partial diplodocid skin impressions in 1990 showed that some species had narrow, pointed,keratinous spines, 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.[31][32] The spines have been incorporated into many recent reconstructions ofDiplodocus, notablyWalking with Dinosaurs.[33] The original description of the spines noted that the specimens in the Howe Quarry nearShell, Wyoming were associated with skeletal remains of an undescribed diplodocid "resemblingDiplodocus andBarosaurus."[31] Specimens from this quarry have since been referred toKaatedocus siberi andBarosaurus sp., rather thanDiplodocus.[8][34]
Fossilized skin ofDiplodocus sp., 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 aroundcrocodilian limbs, 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.[35]
Several elements referred toDiplodocus longus, including atype caudal at the bottom, as figured in Marsh, 1896[36]
The first record ofDiplodocus comes from Marshall P. Felch's quarry atGarden Park nearCañon City,Colorado, when several fossils were collected byBenjamin Mudge andSamuel Wendell Williston in 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 Museum and was namedDiplodocus longus ('long double-beam') bypaleontologistOthniel Charles Marsh in 1878.[37] Marsh namedDiplodocus during theBone Wars, his competition with Philadelphian paleontologistEdward Drinker Cope to collect and describe as many fossil taxa as possible.[38] Though several more complete specimens have been attributed toD. longus,[39][40] 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 Nomenclature was being considered which proposed makingD. carnegii the new type species.[8][41] This proposal was rejected by the ICZN andD. longus has been maintained as the type species, because Hatcher did not demonstrate why the specimen he calledDiplodocus carnegii was not actually just a more complete specimen ofDiplodocus longus.[42]
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 (USNM V 2672), an articulated complete skull, mandibles, and partial atlas was collected in 1883, and was the first complete diplodocid skull to be reported.[43][44] Tschopp et al.'s analysis placed it as an indeterminate diplodocine in 2015 due to the lack of overlap with any diagnosticDiplodocus postcranial material, as was the fate with all skulls assigned toDiplodocus.[8]
Barnum Brown (left) and Henry Osborn (right) excavating a femur of specimen AMNH 223, 1897
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.[38] 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 History all 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.[38] The American Museum of Natural History was the first to launch an expedition, finding a semi-articulated partial postcranial skeleton containing many vertebrae ofDiplodocus in atComo Bluff in 1897. The skeleton (AMNH FR 223) was collected byBarnum Brown andHenry 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 firstDiplodocus mount made—and was the first well preserved individual skeleton ofDiplodocus discovered.[8][39] 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.[8] As seen in the supplementary work done by Suzannah Maidment (2024), AMNH FR 223 also appears to be the geologically youngest specimen ofD. hallorum, as the quarry it was found in is within systems tract 6 (C6), which contains the youngest deposits in the Morrison Formation, as opposed to the other specimens of the taxon which were found in the older systems tract 4 (B4, which dates range from 151.88 Ma to 149.1 Ma).[6][45]
The most notableDiplodocus find also came in 1899, when crew members from theCarnegie Museum of Natural History were collecting fossils in theMorrison Formation ofSheep Creek,Wyoming, with funding from Scottish-American steel tycoonAndrew Carnegie, they discovered a massive and well preserved skeleton ofDiplodocus.[46] The skeleton was collected that year by Jacob L. Wortman and several other crewmen under his direction along with several specimens ofStegosaurus,Brontosaurus parvus, andCamarasaurus preserved alongside the skeleton.[46] The skeleton (CM 84) was preserved in semi articulation and was very complete, including 41 well preserved vertebrae from the midcaudals to 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 ofDiplodocus adjacent to the specimen collected in 1899.[8][46] 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.[46][8] 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"),[8][46] with CM 94 becoming the paratype.[46] There were political reasons rather than scientific for naming the first dinosaur collected by the Carnegie Museum for their patron, Andrew Carnegie.
Hatcher's original composite skeletal reconstruction ofDiplodocus carnegii, 1901
It was not until 1907, that the Carnegie Museum of Natural History created a composite mount ofDiplodocus carnegii that 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.[47][8] 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 City from 1905 to 1928.[48] TheLondon cast specifically became very popular; its casting was requested byKing Edward VII and it was the first sauropod mount put on display outside of the United States.[48] The goal of Carnegie in sending these casts overseas was apparently to bring international unity and mutual interest around the discovery of the dinosaur.[49]
The Carnegie Museum of Natural History made another landmark discovery in 1909 whenEarl Douglass unearthed several caudal vertebrae fromApatosaurus in what is nowDinosaur National Monument on the border region between Colorado and Utah, with the sandstone dating to theKimmeridgian of 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 Holland in detail in 1924, who referred the specimens toD. longus.[50] 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.[8] A nearly complete skull of a juvenileDiplodocus was collected by Douglass in 1921, and it is the first known from aDiplodocus.[51]
AnotherDiplodocus skeleton was collected at the Carnegie Quarry in Dinosaur National Monument, Utah, by theNational Museum of Natural History in 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 Gilmore in 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.[8][52] TheDenver Museum of Nature and Science obtained aDiplodocus specimen through exchange from the Carnegie Museum that had been collected at Dinosaur National Monument. The specimen (DMNH 1494) was nearly as complete as the Smithsonian specimen. It consists of the vertebral column complete from cervical 8 to caudal 20, right scapula-coracoid, complete pelvis, and both hind limbs without feet. It was mounted in the museum during the late 1930s and remounted in the early 1990s. Although not described in detail, Tschopp and colleagues determined that this skeleton also belonged toD. hallorum.[8]
FewDiplodocus finds came for many years until 1979, when three hikers came across several vertebrae stuck in elevated stone next to severalpetroglyphs in 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. Gillette in 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.[18][53] In 2004 and later 2006,Seismosaurus was synonymized withDiplodocus and even suggested to be synonymous with the dubiousD. longus and later Tschoppet al.'s phylogenetic analysis in 2015 supported the idea that many specimens referred toD. longus actually belonged toD. hallorum.[8]
In 1994, theMuseum of the Rockies discovered a very productive fossil site atMother's Day Quarry inCarbon County, Montana from the Salt Wash member of theMorrison Formation that was later excavated by theCincinnati Museum of Natural History and Science in 1996, and after that theBighorn Basin Paleontological Institute in 2017. The quarry was very productive, having mostly isolatedDiplodocus bones 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.[53][35] 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.[54]
Diplodocus is both thetype genus of, and gives its name to, the Diplodocidae, the family in which it belongs.[43] Members of this family, while still massive, have a markedly more slender build than other sauropods, such as thetitanosaurs andbrachiosaurs. 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.[26]
Diplodocus hallorum, first described in 1991 by Gillette asSeismosaurus halli from a partial skeleton comprising vertebrae, pelvis and ribs (specimen NMMNH P-3690).[62] As the specific name honors two people, Jim and Ruth Hall (ofGhost Ranch[63]),George Olshevsky later suggested to emend the name asS. hallorum, using the mandatorygenitive plural; Gillette then emended the name,[18] which usage has been followed by others, including Carpenter (2006).[19] In 2004, a presentation at the annual conference of theGeological Society of America made a case forSeismosaurus being ajunior synonym ofDiplodocus.[64] 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.[65] The position thatD. hallorum should be regarded as a specimen ofD. longus was also taken by the authors of a redescription ofSupersaurus, refuting a previous hypothesis thatSeismosaurus andSupersaurus were the same.[66] 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. longus itself was anomen dubium[8] but a position that was rejected by the International Commission on Zoological Nomenclature as discussed above.
USNM 2672, a skull formerly thought to have belonged to theholotype ofD. 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,[40] 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. carnegii the new type species.[8][41] The proposal was rejected by the ICZN andD. longus has been maintained as the type species.[42] However, in comments responding to the petition, some authors regardedD. longus as potentially valid after all.[67][68]
Diplodocus lacustris ("of the lake") is anomen dubium named 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.[43] The remains are now believed to have been from an immature animal, rather than from a separate species.[69] Mossbruckeret al., 2013 surmised that the dentary and teeth ofDiplodocus lacustris was actually fromApatosaurus ajax.[70] Later in 2015, it was concluded that the snout of the specimen actually belonged toCamarasaurus.[8]
Diplodocus hayi was named byWilliam Jacob Holland in 1924 based on a braincase and partial postcranial skeleton (HMNS 175), including a nearly complete vertebral column, found in the Morrison Formation strata nearSheridan, Wyoming.[8][50]D. hayi remained a species ofDiplodocus until 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 notDiplodocus either and actually referred specimens ofGaleamopus.[8]
Leg bones of young specimens that appear to have become stuck in mud and died,Museum of the Rockies
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.[29] Comparisons between thescleral rings of diplodocines and modern birds and reptiles suggest that they may have beencathemeral, active throughout the day at short intervals.[71]Diplodocus is estimated to have walked at a speed of 1.24 meters per second (4.5 km/h; 2.8 mph).[72]
Marsh and then Hatcher[46] 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 asBrachiosaurus andApatosaurus. A 1951 study byKenneth 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.[73] Since the 1970s, general consensus has the sauropods as firmly terrestrial animals, browsing on trees, ferns, and bushes.[74]
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 amammalian and reptilian system. Reconstructions of the neck and thorax ofDiplodocus show greatpneumaticity, which could have played a role in respiration as it does in birds.[75]
An outdated depiction by Oliver P. Hay (1910), with sprawled limbs[76]
The depiction ofDiplodocus posture has changed considerably over the years. For instance, a classic 1910 reconstruction byOliver P. Hay depicts twoDiplodocus with splayed lizard-like limbs on the banks of a river. Hay argued thatDiplodocus had a sprawling, lizard-like gait with widely splayed legs,[77] and was supported byGustav Tornier. This hypothesis was contested byWilliam Jacob Holland, who demonstrated that a sprawlingDiplodocus would have needed a trench through which to pull its belly.[78] Finds of sauropod footprints in the 1930s eventually put Hay's theory to rest.[74]
Upright neck pose forD. carnegii based on Tayloret al. (2009)
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 ofDiplodocus neck was close to horizontal, rather than vertical, and scientists such as Kent Stevens have used this to argue that sauropods includingDiplodocus did not raise their heads much above shoulder level.[79][80] Anuchal ligament may have held the neck in this position.[79] 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.[81] 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.[82][83]
A reconstruction of the neck ligament structure ofDiplodocus. 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[84]
Another hypothesized neck-supporting ligament is an avian-like elastic ligament, such as that seen inStruthio camelus.[85][86] 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 alltetrapods 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 thatDiplodocus would have held its neck at a more elevated angle than previous studies have concluded.[87] However, this idea might be contradicted due to the inner ear of diplodocoids actually being in alignment for a horizontal neck pose. Also, it is not necessarily accurate to say that the alert pose is the osteologically normal position.[88]
As with the related genusBarosaurus, the very long neck ofDiplodocus is the source of much controversy among scientists. A 1992Columbia 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".[11] 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.[16]
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.[15] This implies that the feeding mechanism ofDiplodocus and other diplodocids was radically different from that of other sauropods. Unilateral branch stripping is the most likely feeding behavior ofDiplodocus,[89][90][91] 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.[15]
Teeth from the Dinosaur National Monument
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.[92] 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.[93]
The flexibility ofDiplodocus neck is debated but it should have been able to browse from low levels to about 4 metres (13 feet) when on all fours.[16][79] However, studies have shown that thecenter of mass ofDiplodocus was very close to thehip socket;[94][95] this means thatDiplodocus 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 postureDiplodocus could potentially increase its feeding height up to about 11 m (36 ft).[95][96]
Diplodocus (dark green) and various sauropods in a tripodal posture, with the white dots showing the approximate center of mass, as estimated in studies
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 whetherDiplodocus 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.[79] 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 likeDiplodocus 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.[97][98] 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 ofDiplodocus andApatosaurus. Taylor found that the neck ofDiplodocus was very flexible, and that Cobley et al. was incorrect, in that flexibility as implied by bones is less than in reality.[99]
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.[100]
Dental microwear patterns ofDiplodocus suggest that it partitioned its resources withCamarasaurus; the former ate softer foods than the latter. However, juvenileCamarasaurus had similar microwear to adultDiplodocus, suggesting that adultDiplodocus may have competed with juvenileCamarasaurus for food.[101]
Diagrams and skull of juvenile specimenCMC VP14128 (left), and diagram showing cranialontogeny
While the long neck has traditionally been interpreted as a feeding adaptation, it was also suggested[102] that the oversized neck ofDiplodocus 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.[103]
While no evidence indicatesDiplodocus nesting habits, other sauropods, such as the titanosaurianSaltasaurus, have been associated with nesting sites.[104][105] 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 documentaryWalking with Dinosaurs portrayed a motherDiplodocus using anovipositor to lay eggs, but it was pure speculation on the part of the documentary author.[33] ForDiplodocus 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.[106]
Based on bonehistology studies in the early 2000s, it was suggested thatDiplodocus and other sauropods grew at a very fast rate, reachingsexual maturity at just over a decade, and continuing to grow throughout their lives.[107][108][109] However, a 2024 study estimated that the holotype ofD. hallorum was around 60 years old in maximum age of death, over 20 years older than the oldest known sauropod specimens, and that it "had 'recently' reached skeletal maturity before death". This would make it one of the oldest known dinosaur specimens. The study also suggested thatD. hallorum may have had a relatively slower and more prolonged rate of growth thanD. carnegii, as the latter reached maturity within just 24 to 34 years of age.[23]
Restoration of a narrow snouted juvenile (based on specimen CMC VP14128) feeding alongside broad snouted adults
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,[110] and 146.8 million years old at the top,[111] which places it in the lateOxfordian,Kimmeridgian, and earlyTithonianages of the Late Jurassic epoch. This formation is interpreted as asemi-arid environment with distinctwet anddry seasons. The Morrison Basin, where many dinosaurs lived, stretched from New Mexico to Alberta and Saskatchewan, and was formed when the precursors to theFront Range of theRocky 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.[112] This formation is similar in age to theLourinha Formation inPortugal and theTendaguru Formation inTanzania.[113]
Diplodocus has been a famous and much-depicted dinosaur as it has been on display in more places than any othersauropod dinosaur.[118]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[119] did much to familiarize it to people worldwide. Casts ofDiplodocus skeletons are still displayed in many museums worldwide, includingD. carnegii in a number of institutions.[74]
The project, along with its association with 'big science',philanthropism, and capitalism, drew much public attention in Europe. The German satirical weeklyKladderadatsch devoted a poem to the dinosaur:
A war machine (landship) fromWorld War I namedBoirault machine was designed in 1915, later deemed impractical and hence given the nickname "Diplodocus militaris".[126]
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