Diplodocus
Diplodocus is an extinct genus of diplodocid sauropod dinosaurs known from the Late Jurassic of North America. The first fossils of Diplodocus were 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 "double" and δοκός "beam", in reference to the double-beamed chevron bones located in the underside of the tail, which were then considered unique.
The genus lived in what is now mid-western North America, at the end of the Jurassic period. It is one of the more common dinosaur fossils found in the middle to upper Morrison Formation, with most specimens being found in rocks dated between about 151.88 and 149.1 million years ago, during the latest Kimmeridgian Age, although it may have made it into the Tithonian, with at least one specimen being potentially from among the youngest deposits of the formation. 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.
Description
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 cantilever bridges. In fact, D. carnegii is currently one of the longest dinosaurs known from a complete skeleton, with a total length of. Modern mass estimates for D. carnegii have tended to be in the range.No skull has ever been found that can be confidently said to belong to Diplodocus, though skulls of other diplodocids closely related to Diplodocus 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, and the neck was composed of at least 15 vertebrae.
Postcranial skeleton
D. 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 to be long based on isometric scaling with D. carnegii. However, he later stated that this was unlikely and estimated it to be long, suggesting that some individuals may have been up to long and weighed 80 to 100 metric tons, making it the longest known dinosaur. The estimated length was later revised downward to and later on to based on findings that show that Gillette had originally misplaced vertebrae 12–19 as vertebrae 20–27. Weight estimates based on the revised length are as high as although more recently, and according to Gregory S. Paul, a long D. hallorum was estimated to weigh in body mass. A study in 2024 later found the mass of a D. hallorum to be only, though the study suggested this only represents the average adult size and not the above average or maximum body size. The nearly complete D. 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 and D. hallorum still remains among the longest known dinosaurs.The estimated tail length of Diplodocus makes up approximately 55% of the total body length, with the tail sometimes hypothesized to be capable of functioning like a very long, tapering bullwhip. This extremely long tail is composed of about 80 caudal vertebrae, which are almost double the number some of the earlier sauropods had in their tails, and far more than contemporaneous macronarians had. Some speculation exists as to whether it may have had a defensive or noisemaking or, as more recently suggested, tactile function. The tail may have served as a counterbalance for the neck. The middle part of the tail had "double beams". 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.
Like other sauropods, the manus 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.
Skin impressions
The discovery of partial diplodocid skin impressions in 1990 showed that some species had narrow, pointed, keratinous spines, much like those on an iguana. The spines could be up to long, on the "whiplash" portion of their tails, and possibly along the back and neck as well, similarly to 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 diplodocid "resembling Diplodocus and Barosaurus." Specimens from this quarry have since been referred to Kaatedocus siberi and Barosaurus sp., rather than Diplodocus.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. These scales range in size and shape depending upon their location on the integument, the smallest of which reach about 1mm while the largest 10 mm. Some of these scales show orientations that may indicate where they belonged on the body. For instance, the ovoid scales are closely clustered together and look similar to scales in modern reptiles that are located dorsally. Another orientation on the fossil consists of arching rows of square scales that interrupts nearby polygonal scale patterning. It is noted that the arching scale rows look similar to the scale orientations seen around crocodilian limbs, suggesting that this area may have also originated from around a limb on the Diplodocus. The skin fossil itself is small in size, reaching less than 70 cm in length. Due to the vast amount of scale diversity seen within such a small area, as well as the scales being smaller in comparison to other diplodocid scale fossils, and the presence of small and potentially "juvenile" material at the Mother's Day Quarry, it is hypothesized that the skin originated from a small or even "juvenile" Diplodocus. In 2025, Gallagher et al. identified probable melanosomes representing diverse colours based on microbodies found within epidermis in the scales of juvenile specimens of Diplodocus sp. from the same quarry, including the specimen first described by Gallagher et al..
Discovery and history
Bone Wars and ''Diplodocus longus''
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. The first specimen was very incomplete, consisting only of two complete caudal vertebrae, a chevron, and several other fragmentary caudal vertebrae. The specimen was sent to the Yale Peabody Museum and was named Diplodocus longus by paleontologist Othniel Charles Marsh in 1878. 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. Though several more complete specimens have been attributed to D. longus, detailed analysis has discovered that this type specimen is actually dubious, which is not an ideal situation for the type species of a well-known genus like Diplodocus. A petition to the International Commission on Zoological Nomenclature was being considered which proposed making D. carnegii the new type species. This proposal was rejected by the ICZN and D. longus has been maintained as the type species, because Hatcher did not demonstrate why the specimen he called Diplodocus carnegii was not actually just a more complete specimen of Diplodocus longus.Although the type specimen was very fragmentary, several additional diplodocid fossils were collected at Felch's quarry from 1877 to 1884 and sent to Marsh, who then referred them to D. longus. One specimen, an articulated complete skull, mandibles, and partial atlas was collected in 1883, and was the first complete diplodocid skull to be reported. Tschopp et al.'s analysis placed it as an indeterminate diplodocine in 2015 due to the lack of overlap with any diagnostic Diplodocus postcranial material, as was the fate with all skulls assigned to Diplodocus.