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",[3][5] in reference to the double-beamed chevron bones located in the underside of the tail, which were then considered unique.

It 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,[6] although it may have made it into the Tithonian.

[7] The Morrison Formation records an environment and time dominated by gigantic sauropod dinosaurs, such as Apatosaurus, Barosaurus, Brachiosaurus, Brontosaurus, and Camarasaurus.

Diplodocus is among the most easily identifiable dinosaurs, with its typical sauropod shape, long neck and tail, and four sturdy legs.

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.

[26] 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.

[30] 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 diplodocid "resembling Diplodocus and Barosaurus.

[6][31] Fossilized skin of Diplodocus sp., discovered at the Mother's Day Quarry, exhibits several different types of scale shapes including rectangular, polygonal, pebble, ovoid, dome, and globular.

[32] The first record of Diplodocus comes from Marshall P. Felch’s quarry at Garden Park near Cañon City, Colorado, when several fossils were collected by Benjamin Mudge and Samuel Wendell Williston in 1877.

[34] Marsh named Diplodocus during the Bone Wars, his competition with Philadelphian paleontologist Edward Drinker Cope to collect and describe as many fossil taxa as possible.

[6] 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.

[35] The American Museum of Natural History was the first to launch an expedition, finding a semi-articulated partial postcranial skeleton containing many vertebrae of Diplodocus in at Como Bluff in 1897.

In 1900, Carnegie crews returned to Sheep Creek, this expedition led by John Bell Hatcher, William Jacob Holland, and Charles Gilmore, and discovered another well preserved skeleton of Diplodocus adjacent to the specimen collected in 1899.

[46] 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.

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.

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.

[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.

A 1951 study by Kenneth 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.

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.

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.

[93][94] 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.

[101] 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.

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.

The Morrison Basin, where many dinosaurs lived, stretched from New Mexico to Alberta and Saskatchewan, and was formed when the precursors to the Front Range of the Rocky Mountains started pushing up to the west.

[109] Dinosaurs known from the Morrison include the theropods Ceratosaurus, Koparion, Stokesosaurus, Ornitholestes, Allosaurus and Torvosaurus, the sauropods Brontosaurus, Apatosaurus, Brachiosaurus, Camarasaurus, and the ornithischians Camptosaurus, Dryosaurus, Othnielia, Gargoyleosaurus and Stegosaurus.

[108] Other vertebrates that shared the same paleoenvironment included ray-finned fishes, frogs, salamanders, turtles like Dorsetochelys, sphenodonts, lizards, terrestrial and aquatic crocodylomorphs such as Hoplosuchus, and several species of pterosaur like Harpactognathus and Mesadactylus.

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[114] did much to familiarize it to people worldwide.

The German satirical weekly Kladderadatsch devoted a poem to the dinosaur: "Le diplodocus" became a generic term for sauropods in French, much as "brontosaur" is in English.