Diplodocus

D. hallorum, known from partial remains, was even larger, and is estimated to have been the size of four

Diplodocus had an extremely long tail, composed of about 80

The discovery of partial diplodocid skin impressions in 1990 showed that some species had narrow, pointed,

The Carnegie Museum of Natural History made another landmark discovery in 1909 when Earl Douglass unearthed several caudal vertebrae from Apatosaurus in what is now Dinosaur National Monument on the border region between Colorado and Utah, with the sandstone dating to the Kimmeridgian of the Morrison 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 by William Jacob Holland in detail in 1924, who referred the specimens to D. longus.^[47] 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 to Diplodocus, but few have been properly described.^[6] A nearly complete skull of a juvenile Diplodocus was collected by Douglass in 1921, and it is the first known from a Diplodocus.^[48]

Another Diplodocus skeleton was collected at the Carnegie Quarry in Dinosaur National Monument, Utah, by the National Museum of Natural History in 1923. The skeleton (USNM V 10865) is one of the most complete known from Diplodocus, consisting of a semi-articulated partial postcranial skeleton, including a well preserved dorsal column. The skeleton was briefly described by Charles Gilmore in 1932, who also referred it to D. longus, and it was mounted in the fossil hall at the National Museum of Natural History the same year. In Emmanuel Tschopp et al.'s phylogenetic analysis of Diplodocidae, USNM V 10865 was also found to be an individual of D. hallorum.^[6][49] The Denver Museum of Nature and Science obtained a Diplodocus 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 to D. hallorum.^[6]

Few Diplodocus finds came for many years until 1979, when three hikers came across several vertebrae stuck in elevated stone next to several petroglyphs in a canyon west of San Ysidro, New Mexico. The find was reported to the New Mexican Museum of Natural History, who dispatched an expedition led by David D. Gillette in 1985, that collected the specimen after several visits from 1985 to 1990. The specimen was preserved in semi-articulation, including 230 gastroliths, 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 the Journal of Paleontology, where Gillette named it Seismosaurus halli (Jim and Ruth Hall's seismic lizard), though in 1994, Gillette published an amendment changing the name to S. hallorum.^[16][50] In 2004 and later 2006, Seismosaurus was synonymized with Diplodocus and even suggested to be synonymous with the dubious D. longus and later Tschopp et al.'s phylogenetic analysis in 2015 supported the idea that many specimens referred to D. longus actually belonged to D. hallorum.^[6]

In 1994, the

A cladogram of the Diplodocidae after Tschopp, Mateus, and Benson (2015) below:^[6]

• Diplodocus carnegii (also spelled incorrectly D. carnegiei), named after
  Pittsburgh, Pennsylvania, and described and named by John Bell Hatcher in 1901.^[58]
• Diplodocus hallorum, first described in 1991 by Gillette as Seismosaurus halli from a partial skeleton comprising vertebrae, pelvis and ribs (specimen NMMNH P-3690).
  junior synonym of Diplodocus.^[61] This was followed by a much more detailed publication in 2006, which not only renamed the species Diplodocus hallorum, but also speculated that it could prove to be the same as D. longus.^[62] The position that D. hallorum should be regarded as a specimen of D. longus was also taken by the authors of a redescription of Supersaurus, refuting a previous hypothesis that Seismosaurus and Supersaurus were the same.^[63] A 2015 analysis of diplodocid relationships noted that these opinions are based on the more complete referred specimens of Diplodocus longus. The authors of this analysis concluded that those specimens were indeed the same species as D. hallorum, but that D. longus itself was a nomen dubium^[6]
  but a position that was rejected by the International Commission on Zoological Nomenclature as discussed above.

• 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 to D. longus,^[37] detailed analysis has suggested that the original fossil lacks the necessary features to allow comparison with other specimens. For this reason, it has been considered a nomen dubium, which Tschopp et al. regarded as not an ideal situation for the type species of a well-known genus like Diplodocus. A petition to the International Commission on Zoological Nomenclature (ICZN) was being considered, which proposed to make D. carnegii the new type species.^[6][38] The proposal was rejected by the ICZN and D. longus has been maintained as the type species.^[39] However, in comments responding to the petition, some authors regarded D. longus as potentially valid after all.^[64][65]
• Diplodocus lacustris ("of the lake") is a nomen dubium named by Marsh in 1884 based on specimen YPM 1922 found by Arthur Lakes, consisting of the snout and upper jaw of a smaller animal from Morrison, Colorado.^[40] The remains are now believed to have been from an immature animal, rather than from a separate species.^[66] Mossbrucker et al., 2013 surmised that the dentary and teeth of Diplodocus lacustris was actually from Apatosaurus ajax.^[67] Later in 2015, it was concluded that the snout of the specimen actually belonged to Camarasaurus.^[6]

• Diplodocus hayi was named by William 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 near Sheridan, Wyoming.^[6][47] D. hayi remained a species of Diplodocus 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 not Diplodocus either and actually referred specimens of Galeamopus.^[6]

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.

The depiction of Diplodocus posture has changed considerably over the years. For instance, a classic 1910 reconstruction by Oliver P. Hay depicts two Diplodocus with splayed lizard-like limbs on the banks of a river. Hay argued that Diplodocus had a sprawling, lizard-like gait with widely splayed legs,^[74] and was supported by Gustav Tornier. This hypothesis was contested by William Jacob Holland, who demonstrated that a sprawling Diplodocus would have needed a trench through which to pull its belly.^[75] Finds of sauropod footprints in the 1930s eventually put Hay's theory to rest.^[71]

Later, diplodocids were often portrayed with their necks held high up in the air, allowing them to graze from tall trees. Studies looking at the morphology of sauropod necks have concluded that the neutral posture of Diplodocus neck was close to horizontal, rather than vertical, and scientists such as Kent Stevens have used this to argue that sauropods including Diplodocus did not raise their heads much above shoulder level.^[77][78] A nuchal ligament may have held the neck in this position.^[77] 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 like Parasaurolophus.^[79] 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.^[80][81] Another hypothesized neck-supporting ligament is an avian-like elastic ligament, such as that seen in Struthio camelus.^[82][83] 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 all tetrapods appear to hold the base of their necks at the maximum possible vertical extension when in a normal, alert posture, and argued that the same would hold true for sauropods barring any unknown, unique characteristics that set the soft tissue anatomy of their necks apart from other animals. The study found faults with Stevens' assumptions regarding the potential range of motion in sauropod necks, and based on comparing skeletons to living animals the study also argued that soft tissues could have increased flexibility more than the bones alone suggest. For these reasons they argued that Diplodocus would have held its neck at a more elevated angle than previous studies have concluded.^[84] 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.^[85]

As with the related genus Barosaurus, the very long neck of Diplodocus is the source of much controversy among scientists. A 1992 Columbia University study of diplodocid neck structure indicated that the longest necks would have required a 1.6-ton heart – a tenth of the animal's body weight. The study proposed that animals like these would have had rudimentary auxiliary "hearts" in their necks, whose only purpose was to pump blood up to the next "heart".^[9] 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.^[14]

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.^[13] This implies that the feeding mechanism of Diplodocus and other diplodocids was radically different from that of other sauropods. Unilateral branch stripping is the most likely feeding behavior of Diplodocus,^[86][87][88] 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.^[13]

Young et 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.^[89] Diplodocine teeth were also continually replaced throughout their lives, usually in less than 35 days, as was discovered by Michael D'Emic et al. Within each tooth socket, as many as five replacement teeth were developing to replace the next one. Studies of the teeth also reveal that it preferred different vegetation from the other sauropods of the Morrison, such as Camarasaurus. This may have better allowed the various species of sauropods to exist without competition.^[90]

The flexibility of Diplodocus neck is debated but it should have been able to browse from low levels to about 4 metres (13 feet) when on all fours.^[14][77] However, studies have shown that the center of mass of Diplodocus was very close to the hip socket;^[91][92] this means that Diplodocus could rear up into a bipedal posture with relatively little effort. It also had the advantage of using its large tail as a 'prop' which would allow for a very stable tripodal posture. In a tripodal posture Diplodocus could potentially increase its feeding height up to about 11 m (36 ft).^[92][93]

The neck's range of movement would have also allowed the head to graze below the level of the body, leading some scientists to speculate on whether Diplodocus grazed on submerged water plants, from riverbanks. This concept of the feeding posture is supported by the relative lengths of front and hind limbs. Furthermore, its peg-like teeth may have been used for eating soft water plants.^[77] Matthew Cobley et al. (2013) disputed this, finding that large muscles and cartilage would have limited neck movements. They state that the feeding ranges for sauropods like Diplodocus were smaller than previously believed and the animals may have had to move their whole bodies around to better access areas where they could browse vegetation. As such, they might have spent more time foraging to meet their minimum energy needs.^[94][95] The conclusions of Cobley et 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 of Diplodocus and Apatosaurus. Taylor found that the neck of Diplodocus was very flexible, and that Cobley et al. was incorrect, in that flexibility as implied by bones is less than in reality.^[96]

In 2010, Whitlock et al. described a juvenile skull at the time referred to Diplodocus (CM 11255) that differed greatly from adult skulls of the same genus: its snout was not blunt, and the teeth were not confined to the front of the snout. These differences suggest that adults and juveniles were feeding differently. Such an ecological difference between adults and juveniles had not been previously observed in sauropodomorphs.^[97]

While the long neck has traditionally been interpreted as a feeding adaptation, it was also suggested^[98] that the oversized neck of Diplodocus and its relatives may have been primarily a sexual display, with any other feeding benefits coming second. A 2011 study refuted this idea in detail.^[99]

While no evidence indicates Diplodocus nesting habits, other sauropods, such as the titanosaurian Saltasaurus, have been associated with nesting sites.^[100][101] The titanosaurian nesting sites indicate that they may have laid their eggs communally over a large area in many shallow pits, each covered with vegetation. Diplodocus may have done the same. The documentary Walking with Dinosaurs portrayed a mother Diplodocus using an ovipositor to lay eggs, but it was pure speculation on the part of the documentary author.^[30] For Diplodocus and other sauropods, the size of clutches and individual eggs were surprisingly small for such large animals. This appears to have been an adaptation to predation pressures, as large eggs would require greater incubation time and thus would be at greater risk.^[102]

Based on bone histology studies in the early 2000s, it was suggested that Diplodocus and other sauropods grew at a very fast rate, reaching sexual maturity at just over a decade, and continuing to grow throughout their lives.^{[103][104][105]} However, a 2024 study estimated that the holotype of D. 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 that D. hallorum may have had a relatively slower and more prolonged rate of growth than D. carnegii, as the latter reached maturity within just 24 to 34 years of age.^[20]

The Morrison Formation is a sequence of shallow marine and alluvial sediments which, according to

Museo de La Plata

Diplodocus has been a famous and much-depicted dinosaur as it has been on display in more places than any other

sauropod dinosaur.^[114]

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^[115] did much to familiarize it to people worldwide. Casts of Diplodocus skeletons are still displayed in many museums worldwide, including D. carnegii in a number of institutions.^[71]

The project, along with its association with 'big science',

philanthropism, and capitalism, drew much public attention in Europe. The German satirical weekly Kladderadatsch

devoted a poem to the dinosaur:

Auch ein viel älterer Herr noch muß Den Wanderburschen spielen Er ist genannt Diplodocus und zählt zu den Fossilen Herr Carnegie verpackt ihn froh In riesengroße Archen Und schickt als Geschenk ihn so An mehrere Monarchen[116]

But even a much older gent Sees itself forced to wander He goes by the name Diplodocus And belongs among the fossils Mr. Carnegie packs him joyfully Into giant arks And sends him as gift To several monarchs

"Le diplodocus" became a generic term for sauropods in French, much as "brontosaur" is in English.[117]

D. longus is displayed the

Senckenberg Museum in Frankfurt (a skeleton made up of several specimens, donated in 1907 by the American Museum of Natural History), Germany.^[118][119] A mounted and more complete skeleton of D. longus is at the Smithsonian National Museum of Natural History in Washington, DC,^[120] while a mounted skeleton of D. hallorum (formerly Seismosaurus), which may be the same as D. longus, can be found at the New Mexico Museum of Natural History and Science.^[121]

A war machine (landship) from WW1 named Boirault machine was designed in 1915, later deemed impractical and hence given the nickname "Diplodocus militaris".^[122]

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External links

Wikimedia Commons has media related to Diplodocus.

Wikispecies has information related to Diplodocus.

• Diplodocus in the Dino Directory
• Museo Nacional de Ciencias Naturales, Madrid
• Diplodocus Marsh, by J.B. Hatcher 1901 – Its Osteology, Taxonomy, and Probable Habits, with a Restoration of the Skeleton. Memoirs of the Carnegie Museum, Volume 1, Number 1, 1901. Full text, Free to read.
• Skeletal restorations of diplodocids including D. carnegii, D. longus, and D. hallorum, from Scott Hartman's Skeletal Drawing website.