Diplodocus

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Diplodocus Fossil range: Late Jurassic
Diplodocus skull
Conservation status
Exinct (fossil)
Scientific classification
Kingdom: Animalia Phylum: Chordata Class: Sauropsida Superorder: Dinosauria Order: Saurischia Suborder: Sauropodomorpha Infraorder: Sauropoda Family: Diplodocidae Genus: Diplodocus Marsh, 1878

Diplodocus (pronounced /ˌdɪ.pləˈdɔ.kəs/ or /dɪˈplɔd.əkəs/; meaning "double beam") is a genus of diplodocid sauropod dinosaur which lived in what is now western North America at the end of the Jurassic Period. The generic name is in reference to its double-beamed chevron bones (Greek diplos/διπλος meaning 'double' and dokos/δοκος meaning 'wooden beam' or 'bar').^[1]

Diplodocus, a herbivorous sauropod dinosaur, was one of the more common dinosaurs found in the Upper Morrison Formation, about 150 to 147 million years ago, in an environment and time dominated by giant sauropods , such as Camarasaurus, Barosaurus, Apatosaurus and Brachiosaurus. It is among the most easily identifiable dinosaurs, with its classic dinosaur shape, long neck and tail and four sturdy legs. For many years it was the longest dinosaur known. Its great size may have been a deterrent to predators such as Allosaurus and Ceratosaurus.

Contents 1 Description 2 Discovery and species 3 Palaeobiology 3.1 Neck 3.2 Tail 3.3 Trunk 4 Classification 5 In popular culture 6 Footnotes 7 External links

[edit] Description

One of the best known sauropods, Diplodocus was a very large long-necked quadrupedal animal, with a long, whip-like tail. Its forelimbs were slightly shorter than its hind limbs, resulting in a largely horizontal posture. The long-necked, long-tailed animal with four sturdy legs has been mechanically compared with a suspension bridge.^[2]

The skull of Diplodocus was very small, compared to the size of the animal, which could reach up to 27 metres (90 feet).

Diplodocus was herbivorous. Its small teeth were peg-like and positioned only in the anterior part of the jaws. Its braincase was small. The neck was composed of at least fifteen vertebrae.

Diplodocus is the longest dinosaur known from a complete skeleton. While dinosaurs such as Seismosaurus (which might be a large Diplodocus) and Supersaurus were probably longer, fossil remains of these animals are only fragmentary.^[3]

[edit] Discovery and species

Several species of Diplodocus were described between 1878 and 1924. The first skeleton was found at Como Bluff, Wyoming by Benjamin Mudge and Samuel Wendell Williston in 1878 and was named Diplodocus longus ("long double-beam"), by palaeontologist Othniel Charles Marsh in 1878.^[4] Marsh later named D. lacustris in 1884, from remains of a smaller animal from Morrison, Colorado.^[5] These remains are now believed to have been from an immature animal, rather than from a separate species. Although not the type species, D. carnegiei (named after Andrew Carnegie) is the best known, mainly 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. hayi, known from a partial skeleton discovered by William H. Utterback in 1902 near Sheridan, Wyoming, was described in 1924.^[6]

Diplodocus remains have been found in the Morrison Formation of the western U.S. States of Colorado, Utah, Montana and Wyoming. Fossils of this animal are common, except for the skull, which is often missing from otherwise complete skeletons.

Diplodocus species:

• D. longus, Marsh 1878; holotype
• D. carnegiei, Hatcher 1901
• D. hayi, Holland 1924

• D. hallorum =Seismosaurus hallorum
• D. lacustris is nomen dubium

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.^[7]

As with the related genus Barosaurus, the very long neck of Diplodocus' is the source of much controversy amongst scientists. A 1992 Columbia University study of Diplodocid neck structure indicated that the longest 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 only purpose was to pump blood up to the next 'heart' (Lambert).

A presentation^[8] at the annual conference of the Geological Society of America, in 2004, made a case for Seismosaurus, discovered in 1979 and recognised as a separate genus in 1991, to be reassigned as a species of Diplodocus, namely D. hallorum.

[edit] Palaeobiology

Due to a wealth of skeletal remains, Diplodocus is one of the best studied dinosaurs. Many aspects of its lifestyle have been subject to various theories over the years. Marsh and then Hatcher^[9] assumed the animal was aquatic, due to the position of its nasal openings at the apex of the cranium. A classic 1910 reconstruction by Oliver P. Hay [1]depicts two Diplodocus with splayed lizardlike limbs on the banks of a river.

The idea of an aquatic existence was later debunked as the water pressure on the chest wall of Diplodocus would have been too great for the animal to have breathed. Since the 1970s, general consensus has the sauropods as firmly terrestrial animals, browsing on trees. Later still, interestingly, with the preceding view of its possible preference for water plants there is a view of a likely riparian habitat for Diplodocus, echoing the original aquatic theory.

[edit] Neck

At first, diplodocids were often portrayed with their necks held high up in the air, allowing them to graze from tall trees. More recently, scientists have argued that the heart would have had trouble sustaining sufficient blood pressure to oxygenate the brain. Furthermore, more recent studies^[10] have shown that the structure of the neck vertebrae would not have permitted the neck to bend far upwards. Interestingly, the range of movement of the neck would have allowed the head to graze below the level of the body, leading 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 peglike teeth may have been used for eating soft water plants.^[10]

[edit] Tail

Diplodocus had an extremely long tail, composed of at around eighty caudal vertebrae,^[11] which is almost double the number some of the earlier sauropods had in their tails; Shunosaurus having 43 and Camarasaurus 53. There has been speculation as to whether it may have had a defensive^[12] or noisemaking function.^[13]

The tail may have served as a counterbalance for the neck. The middle part of the tail had 'double beams' (oddly-shaped bones on the underside of the tail), which gave Diplodocus 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.

[edit] Trunk

There has been speculation over whether the high nasal openings in the skull meant that Diplodocus may have had a trunk. A recent study^[14] surmised there was no paleoneuroanatomical evidence for a trunk. It noted that the facial nerve in an animal with a trunk, such as an elephant, is large as it innervates the trunk. The evidence is that it is very small in Diplodocus.

[edit] Classification

Diplodocus gives its name to Diplodocidae, the family in which it belongs.^[5] Members of this family, while still massive, are of a markedly more slender build compared with other sauropods such as the titanosaurs and brachiosaurs. All are characterised by long necks and tails and a horizontal posture, with forelimbs shorter than hindlimbs. Diplodocids flourished in the late Jurassic of North America and possibly Africa^[11] and appear to have been replaced by titanosaurs in the Cretaceous.

A subfamily, Diplodocinae, has been created to include Diplodocus and its closest relatives, including Seismosaurus, which may belong to the same genus, and Barosaurus. More distantly related is the contemporaneous Apatosaurus, which is still considered a diplodocid although not a diplodocine.^[15][16] The Portuguese Dinheirosaurus and the African Tornieria have also been identified as close relatives of Diplodocus by some authors.^[17][18]

[edit] In popular culture

Mounted Casts of Diplodocus skeletons are displayed in many museums worldwide, including an unusual D. hayi in the Houston Museum of Natural Science, and D. carnegiei in the Natural History Museum in London, the Natural Science Museum in Madrid, Spain, the Senckenberg Museum in Frankfurt, Germany, the Field Museum of Natural History in Chicago and, of course, the Carnegie Museum of Natural History in Pittsburgh. A mounted skeleton of D. longus is at the Smithsonian National Museum of Natural History in Washington, D. C..

Diplodocus was featured in the second episode of the award-winning BBC television series Walking With Dinosaurs. The episode "Time of the Titans" follows the life of a simulated Diplodocus 152 million years ago.

In the animated film The Land Before Time VI: The Secret of Saurus Rock, the character "Doc" (presumably short for Diplodocus), voiced by Kris Kristofferson, was a Diplodocus; in contrast to the "long-neck" protagonists, which were Apatosaurus.

Diplodocus had cameo appearances in The Land That Time Forgot and in The Lost World (2001).

[edit] Footnotes

[edit] External links

• 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.
• Carnegie Museum of Natural History - History