Diplodocus

Diplodocus (/dɪˈplɒdəkəs/, /daɪˈplɒdəkəs/, or /ˌdɪploʊˈdoʊkəs/) is a genus of diplodocid sauropod dinosaurs whose fossils were first discovered in 1877 by S. W. Williston. The generic name, coined by Othniel Charles Marsh in 1878, is a neo-Latin term derived from Greek διπλός (diplos) "double" and δοκός (dokos) "beam", in reference to the double-beamed chevron bones located in the underside of the tail, which were then considered unique. It is now common scientific opinion that Seismosaurus hallorum is a species of Diplodocus.

This genus of dinosaurs lived in what is now mid-western North America at the end of the Jurassic period. Diplodocus is one of the more common dinosaur fossils found in the middle to upper Morrison Formation, between about 154 and 152 million years ago, during the late Kimmeridgian age.The Morrison Formation records an environment and time dominated by gigantic sauropod dinosaurs, such as Apatosaurus , Barosaurus, Brachiosaurus , Brontosaurus , and Camarasaurus . Its great size may have been a deterrent to the predators Allosaurus and Ceratosaurus: their remains have been found in the same strata, which suggests that they coexisted with Diplodocus.

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 of Diplodocus carnegii (green) and D. hallorum (orange) compared with a human.
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 with suspension bridges. In fact, Diplodocus carnegii is currently one of the longest dinosaurs known from a complete skeleton, with a total length of 24 meters (79 ft). Modern mass estimates for Diplodocus carnegii have tended to be in the 11–14.8-metric-ton (12.1–16.3-short-ton) range.

Diplodocus hallorum, known from partial remains, was even larger, and is estimated to have been the size of four elephants. When first described in 1991, discoverer David Gillette calculated it may have been up to 52 m (171 ft) long,making it the longest known dinosaur (excluding those known from exceedingly poor remains, such as Amphicoelias). Some weight estimates of this time ranged as high as 113 metric tons (125 short tons). The estimated length was later revised downward to 33–33.5 m (108–110 ft) and later on to 32 m (105 ft) based on findings that show that Gillette had originally misplaced vertebrae 12–19 as vertebrae 20–27. The nearly complete Diplodocus carnegii skeleton at the Carnegie Museum of Natural History in Pittsburgh, Pennsylvania, on which size estimates of D. hallorum are mainly based, also was found to have had its 13th tail vertebra come from another dinosaur, throwing off size estimates for D. hallorum even further. While dinosaurs such as Supersaurus were probably longer, fossil remains of these animals are only fragmentary.

Caudal vertebrae of D. carnegii showing the double-beamed chevron bones to which the genus name refers, Natural History Museum, London
Diplodocus had an extremely long tail, composed of about 80 caudal vertebrae, which are almost double the number some of the earlier sauropods had in their tails (such as Shunosaurus with 43), and far more than contemporaneous macronarians had (such as Camarasaurus with 53). Some speculation exists as to whether it may have had a defensive or noisemaking (by cracking it like a coachwhip) function. 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 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. Chevron bones of this particular form were initially believed to be unique to Diplodocus; since then they have been discovered in other members of the diplodocid family as well as in non-diplodocid sauropods, such as Mamenchisaurus.

Restoration of D. carnegii with horizontal neck, flexible whip tail, keratinous spines and nostrils low on the snout
Like other sauropods, the manus (front "feet") of Diplodocus 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.

No skull has ever been found that can be confidently said to belong to Diplodocus, though skulls of other diplodocids closely related to Diplodocus (such as Galeamopus) are well known. The skulls of diplodocids were very small compared with the size of these animals. Diplodocus had small, 'peg'-like teeth that pointed forward and were only present in the anterior sections of the jaws. Its braincase was small. The neck was composed of at least 15 vertebrae and may have been held parallel to the ground and unable to be elevated much past horizontal.

The discovery of partial diplodocid skin impressions in 1990 showed that some species had narrow, pointed keratinous spines, much like those on an iguana and up to 18 centimeters (7.1 in) long, on the "whiplash" portion of their tails, and possibly along the back and neck as well, as in hadrosaurids. The spines have been incorporated into many recent reconstructions of Diplodocus, notably Walking with Dinosaurs.The original description of the spines noted that the specimens in the Howe Quarry near Shell, Wyoming were associated with skeletal remains of an undescribed diplodocids "resembling Diplodocus and Barosaurus." Specimens from this quarry have since been referred to Kaatedocus siberi and Barosaurus sp., rather than Diplodocus

   the Seismosaurus was longer than any sauropod surpassing supersaurus and it was a light blue skin with lighter blue on the back

   one species is orange in color and has blue , and stripes all over its body

    another is more grey with a lighter underbelly and one individual is known for a scar across his face

    one more species is more brown in coloration and has spines down its back like many of its species