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Diplodocus
Temporal range: Late Jurassic
Diplo.jpg
An artist's illustration of Diplodocus longus
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Order: Saurischia
Family: Diplodocidae
Subfamily: Diplodocinae
Genus: Diplodocus
Marsh, 1878
Type species
Diplodocus longus
nomen dubium
Marsh, 1878
Referred species
  • Diplodocus carnegii (Hatcher, 1901)
  • Diplodocus hallorum (Gillette, 1991)
    (originally Seismosaurus)
Synonyms
  • Seismosaurus Gillette, 1991


Diplodocus (di·plod·o·cus) was a species of diplodocid sauropod dinosaur that lived in western North America during the late Jurassic period, 154 to 150 million years ago.[1] It is often thought that the longest species, Diplodocus hallorum, is usually called by the synonym Seismosaurus. It had a long tail, very similar to a bullwhip. It also had a narrow, shallow head, which is an identifying feature in the Land Before Time films and episodes but was not so much in real life, and one sharp claw on each front foot.

DescriptionEdit

One of the best-known sauropods, Diplodocus was a large long-necked four-legged animal, with a long, whip-like tail. Its front limbs were a bit shorter than its hind limbs, which forms a horizontal stance for the most part. The long-necked, long-tailed animal with four sturdy legs has been mechanically compared with a suspension bridge. In fact, Diplodocus is the longest dinosaur known from a complete skeleton.[2] Diplodocus species ranged from 80–115 ft (26-35 m) and weighed 10-16 metric tons.[3][4][5][6]

The skull of Diplodocus was very small, compared with the size of the animal, which could reach up to 115 ft,[7] of which over 20 ft was neck.[8] Diplodocus had small, 'peg'-like teeth that pointed forward and were only found in the front of the jaws.[9] The neck was formed by at least 15 vertebrae and is now believed to have been held parallel to the ground most of the time and unable to have been raised much past horizontal.[10]

Diplodocus had an 8 m long neck and a short 6 ft head. Its 14 m long tail had 80 vertebrae,[11] and might have been used like a whip either to attack predators [12] or to make whip-cracking noises.[13] The tail may have served as a counterbalance for the neck. The tail vertebrae had double beams (hence the name Diplodocus: double beam) that may have protected the blood vessels from being crushed if the tail pressed against the ground.

Like most sauropods, the front "feet" of Diplodocus were highly modified, with the finger and hand bones arranged upright, horseshoe-shaped in cross section. Diplodocus lacked claws on all but one toe of the front limb, and this claw was strangely large compared to other sauropods, flat from side to side, and detached from the bones of the hand. The role of this odd skilled claw is not known.[14]

HistoryEdit

Several species of Diplodocus were described from 1878 and 1924. The first skeleton was found at Cañon City, Colorado by Benjamin Mudge and Samuel Wendell Williston in 1877, and was named Diplodocus longus ('long double-beam'), by paleontologist Othniel Charles Marsh in 1878.[15] Diplodocus remains have since been found in the Morrison Formation of the U.S. States of Colorado, Utah, Montana and Wyoming. Fossils of this animal are common, except for the skull. Although not the type species, D. carnegii is the best known and most famous due to the large number of casts of its skeleton in museums around the world.

The two Morrison Formation sauropod genera Diplodocus and Barosaurus had very similar limb bones. In the past, many isolated limb bones were automatically attributed to Diplodocus but may, in fact, have belonged to Barosaurus.[16]

Valid speciesEdit

  • D. longus, the type species, is known from two skulls and some tail bones from the Morrison Formation of Colorado and Utah [17]
  • D. carnegii (also spelled D. carnegiei), named after Andrew Carnegie, is the best known, due to a near-complete skeleton collected by Jacob Wortman, of the Carnegie Museum of Natural History in Pittsburgh, Pennsylvania and described and named by John Bell Hatcher in 1901.
  • D. hallorum, best known as Seismosaurus hallorum.[18] In 2004, a presentation at the annual conference of the Geological Society of America showed that Seismosaurus was in fact a species of Diplodocus.[19] 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.[20] The position that D. hallorum should be regarded as a specimen of D. longus was also taken by the authors of a new description of Supersaurus, refuting a previous hypothesis that Seismosaurus and Supersaurus were the same.[21][22] It is now believed to be from an immature animal, not a separate species [23]

Doubtful speciesEdit

  • D. lacustris, named by Marsh in 1884, from remains of a small animal from Morrison, Colorado.

ClassificationEdit

Diplodocus is the type genus of Diplodocidae.[24] Members of this family, while still of great size,have a thinner build than other sauropods, such as the titanosaurs and brachiosaurs. All are marked by long necks and tails and a horizontal stance, with front legs shorter than the back legs. Diplodocids ruled North America and possibly Africain the Late Jurassic.[25]

A subfamily, Diplodocinae, was built to include Diplodocus and its kin, including Barosaurus. More distantly related is the co-existing Apatosaurus, which is still considered a diplodocid though not a diplodocine, as it is a member of the subfamily Apatosaurinae. Dinheirosaurus and Tornieria have also been identified as close relatives of Diplodocus by some authors.

The Diplodocoidea includes the diplodocids, as well as dicraeosaurids, rebbachisaurids, Suuwassea, Amphicoelias,[26][27][28][29] and possibly Haplocanthosaurus, and/or the nemegtosaurids. This clade is the sister group to, Camarasaurus, brachiosaurids and titanosaurians; the Macronaria.[30][31]

PaleobiologyEdit

PostureEdit

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,[32] and was supported by Gustav Tornier. However, this hypothesis was challenged by W. J. Holland, who showed that a sprawling Diplodocus would have needed a trench to pull its belly through.[33]

Later, diplodocids were often portrayed with their necks held high up in the air, letting them graze from tall trees. Studies with computer models have shown that neutral pose of the neck was horizontal, not vertical. Scientists such as Kent Stephens have used this to argue that sauropods like Diplodocus did not raise their heads much past shoulder level,[34][35] but studies to come showed that all tetrapods seem to hold their necks at the maximum possible vertical extension when in a normal, alert posture, and argued that the same would hold true for sauropods with unknown, unique traits that set the soft tissue form of their necks apart from other animals. One of the sauropod models was Diplodocus, which they found would have held its neck at about a 45 degree angle with the head pointed down in a resting pose.[36]

As with the Barosaurus, the long neck of Diplodocus is the source of much controversy among scientists. A 1992 Columbia University study of Diplodocid neck structure indicated that the such long necks would have required a 1.6 ton heart. The study proposed that animals like these would have had rudimentary auxiliary 'hearts' in their necks, whose sole purpose was to pump blood up to the next 'heart'.[37]

While the long neck has traditionally been seen as a feeding adaptation, it was suggested [38] that the oversized neck of Diplodocus and its relatives may have been primarily a sexual display, and feeding benefits would come nest, but a recent study refuted this idea in detail.[39]

FoodEdit

Diplodocus has strange teeth compared to other sauropods. The crowns are long and thin, egg-shaped in cross-section, while the top forms a blunt triangular point. The most prominent wear facet is on the apex, though unlike all other wear patterns seen in sauropods, Diplodocus wear patterns are on the cheek of both the top and bottom teeth.[40] What this means is Diplodocus and other diplodocids had a radically different feeding mechanism than other sauropods. Branch stripping with one side of the mouth is the most likely feeding behavior of Diplodocus,[41][42][43] as it explains the strange wear patterns of the teeth (from tooth–food contact). To strip a branch with one side of the mouth, one tooth row would have been used to strip leaves from the stem, while the other would act as a guide and stabilizer. With the long part of the skull in front of the eyes, it could strip a lot more stems in one move. The backwards motion of the lower jaws could have contributed two useful roles to feeding behaviour: 1) an increased gape, and 2) allowed fine adjustments of the relative positions of the tooth rows, creating a smooth stripping action.[44]

With a flexible neck, and the option to use its tail and rear up on its hind limbs, Diplodocus would have had the ability to browse at many levels (low, medium, and high), up to 33 ft from the ground.[45] The neck's range of movement may have let Diplodocus graze on submerged water plants, from riverbanks. This concept is backed up by the lengths of front and hind limbs. Plus, its peg-like teeth may have been used to eat soft water plants.[46]

Other anatomicalEdit

The head of Diplodocus has been widely shown with the nostrils on top due to the position of the nasal openings at the apex of the skull. There has been speculation to whether such a setup meant that Diplodocus may have had a trunk.[47] A new study [48] said there was no evidence for a trunk. It noted that the facial nerve in an animal with a trunk, such as an elephant, is large as it supplies the trunk. The suggests that the facial nerve is too small in Diplodocus. Studies by Lawrence Witmer (2001) indicated that, while the nasal openings were high on the head, the actual, fleshy nostrils were much lower down on the snout.[49]

Recent findings have shown that Diplodocus and other diplodocids may have had thin, pointed spines on their back, much like those on an iguana.[50][51] This radically different look has been built in recent reconstructions, like Walking with Dinosaurs. It's not known just how many diplodocids had this trait, and if it was there in other sauropods.

Reproduction and GrowthEdit

While there is no proof for Diplodocus nesting habits, other sauropods such as the titanosaurian Saltasaurus have been linked with nesting sites.[52][53] The titanosaurian nesting sites show that may have laid their eggs communally over a large area in a lot of shallow pits, each covered with plants. It is possible that Diplodocus may have done the same.

Diplodocus, as well as other sauropods, grew at a fast rate, and reached sexual maturity in just a decade, though they kept growing through their lives.[54][55][56] It was once thought that sauropods would grow slowly through their life, taking decades to reach maturity. Dara

180px-Dipldocus

Diplodocus, correctly restored with spines on it's back, from Walking with Dinosaurs.

640px-WWDBook Diplodocus

In the MediaEdit

Diplodocus appears briefly at the beginning of the Disney Pixar film The Good Dinosaur, along with a Parasaurolophus.
Good Dinosaur Parasaurolophus and Diplodocus

Diplodocus on the right side next to Parasaurolophus.

ReferencesEdit

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