Diplodocus

Diplodocus is an extinct kind of long-necked dinosaur called a sauropod. It belonged to a group known as diplodocids. Its fossils have been found in North America and Europe, from the Late Jurassic period. The first fossils of Diplodocus were discovered in 1877 by S. W. Williston. The name was given by Othniel Charles Marsh in 1878. It comes from Greek words meaning "double" and "beam," which refers to the double-beamed chevron bones on the underside of its tail. At the time, these bones were thought to be unique.

Diplodocus 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. Most of its fossils come from rocks that are about 151.88 to 149.1 million years old, from the latest Kimmeridgian Age. It may also have lived into the Tithonian, and at least one specimen (AMNH FR 223) may come from some of the youngest rocks of the formation.

The Morrison Formation shows a time and place dominated by huge sauropod dinosaurs. These included Apatosaurus, Barosaurus, Brachiosaurus, Brontosaurus, and Camarasaurus. Diplodocus's great size may have helped protect it from the predators Allosaurus and Ceratosaurus. Remains of these predators have been found in the same rock layers, which suggests that they lived at the same time as Diplodocus.

Description

Diplodocus were among the best-known sauropods. They were very large, long-necked, quadrupedal animals with long, whip-like tails. Their forelimbs were slightly shorter than their hind limbs, so they held their bodies in a largely horizontal posture, and their skeletons have been compared with cantilever bridges. D. carnegii is one of the longest dinosaurs known from a complete skeleton, at 24–26 meters (79–85 ft) long. No skull has been confidently identified as belonging to Diplodocus, but skulls of close relatives such as Galeamopus are well known, and they were very small compared with the size of the animals. Diplodocus had small, peg-like teeth that pointed forward and were only in the anterior parts of the jaws. D. hallorum, known from partial remains, was even larger, about the size of four elephants. Its size estimates have changed over time as scientists studied the fossils more closely. The animal's tail was about 55% of its total body length and was made of about 80 caudal vertebrae. Some scientists have suggested the tail may have worked like a bullwhip or a coachwhip.

The middle of the tail had unusual "double beam" bones on its underside, which gave Diplodocus its name. These bones were once thought to be unique to Diplodocus, but similar bones have since been found in other diplodocid dinosaurs and in Mamenchisaurus. The front feet were arranged into a column, and most toes had no claws. The skin of some diplodocids had narrow, pointed spines, much like those of an iguana. These spines may have been along the tail and possibly the back and neck, similar to some hadrosaurids. Fossilized skin from the Mother's Day Quarry shows many different scale shapes, some of which look similar to those seen around the limbs of a crocodilian. Scientists think this skin may have come from a small or young Diplodocus.

Discovery and history

The first known Diplodocus fossils were collected in 1877 at Garden Park near Cañon City, Colorado, by Benjamin Mudge and Samuel Wendell Williston. That first specimen was very incomplete. It was sent to the Yale Peabody Museum, and in 1878 the paleontologist Othniel Charles Marsh named it Diplodocus longus ('long double-beam'). Marsh named it during the Bone Wars, his competition with Edward Drinker Cope to collect and describe as many fossil types as possible. Later studies found this first specimen to be doubtful, so a petition to the International Commission on Zoological Nomenclature proposed making D. carnegii the new type species. The commission rejected this, so D. longus remained the type species. More fossils were found at the same quarry from 1877 to 1884, including a complete skull collected in 1883 and sent to the National Museum of Natural History.

After the Bone Wars, big museums in the eastern United States wanted their own dinosaur collections. The American Museum of Natural History, the Carnegie Museum of Natural History, and the Field Museum of Natural History all sent expeditions west to find the most complete sauropod. In 1897, the American Museum's expedition found a partial skeleton at Como Bluff, collected by Barnum Brown and Henry Osborn. Later work in Diplodocidae showed it belonged to the species D. hallorum. In 1899, an expedition funded by Andrew Carnegie found a large, well-preserved Diplodocus skeleton in the Morrison Formation at Sheep Creek, Wyoming, alongside Stegosaurus, Brontosaurus parvus, and Camarasaurus. In 1900, a second Carnegie expedition led by John Bell Hatcher, William Jacob Holland, and Charles Gilmore found another skeleton nearby. Hatcher named the 1899 skeleton Diplodocus carnegii after Carnegie. By 1907, the Carnegie Museum had built a full display skeleton nicknamed "Dippy." Casts were sent to museums in London, Berlin, Paris, Vienna, Bologna, St. Petersburg, Buenos Aires, Madrid, and Mexico City. The London cast was requested by King Edward VII and was the first sauropod display shown outside the United States.

In 1909, Earl Douglass found Apatosaurus tail bones at what is now Dinosaur National Monument, where the rocks date to the Kimmeridgian of the Morrison Formation. Excavations there lasted until 1922 and uncovered many dinosaurs. Several Diplodocus skulls were found there in 1912, 1915, and 1923, and Holland described them in 1924. In 1923, the National Museum of Natural History collected a nearly complete Diplodocus skeleton from the same area, which Gilmore described in 1932. The Denver Museum of Nature and Science later obtained another specimen from the Carnegie Museum, which was also found at the Monument.

Few Diplodocus finds were made for many years. In 1979, three hikers in New Mexico noticed vertebrae stuck in stone near some petroglyphs, west of San Ysidro, New Mexico. The find was reported to the New Mexican Museum of Natural History, and an expedition led by David D. Gillette collected it between 1985 and 1990. The specimen included 230 gastroliths and was named Seismosaurus halli in 1991 in the Journal of Paleontology. In 1994, the Museum of the Rockies found a rich fossil site at Mother's Day Quarry in Carbon County, Montana. It was later dug up by the Cincinnati Museum of Natural History and Science in 1996 and by the Bighorn Basin Paleontological Institute in 2017. The quarry had many Diplodocus bones from young and adult animals, including skin impressions and pathologies. Two partial skeletons found in the Lourinhã Formation of Portugal were thought to be closely related to Diplodocus. In 2026, Diplodocus remains were found in the Villar del Arzobispo Formation of Spain.

Classification and species

Diplodocus is the type genus of the Diplodocidae, the family it belongs to and gives its name to. Diplodocids were still huge, but they were much more slender than other sauropods such as titanosaurs and brachiosaurs. They all had long necks and tails, a horizontal posture, and shorter front legs than back legs. They lived in the Late Jurassic of North America and possibly Africa. The Diplodocinae subfamily includes Diplodocus and its closest relatives, such as Barosaurus. Apatosaurus lived at the same time and is a diplodocid, but it belongs to the sister subfamily Apatosaurinae. Some scientists also link the Portuguese Dinheirosaurus and the African Tornieria to Diplodocus. The wider group Diplodocoidea includes the diplodocids, dicraeosaurids, rebbachisaurids, Suuwassea, Amphicoelias, possibly Haplocanthosaurus, and/or the nemegtosaurids. This clade is the sister group to Macronaria, which includes camarasaurids, brachiosaurids, and titanosaurians. A cladogram of the Diplodocidae is shown below.

The best-known species is Diplodocus carnegii, named after Andrew Carnegie. It is famous mainly because of a nearly complete skeleton called Dippy, collected by Jacob Wortman of the Carnegie Museum of Natural History in Pittsburgh, Pennsylvania. John Bell Hatcher described and named it in 1901. Diplodocus hallorum was first described in 1991 as Seismosaurus halli from a partial skeleton. Its name honors Jim and Ruth Hall of Ghost Ranch, and it was later changed using the genitive plural. In 2004, a talk at the Geological Society of America suggested that Seismosaurus was a junior synonym of Diplodocus. A 2006 study renamed it Diplodocus hallorum and suggested it might be the same as D. longus. A later study of Supersaurus also took this view.

Some names are called nomen dubium (doubtful names) because the fossils are not clear enough to be sure. Diplodocus longus, the type species, is known from a few tail bones from Colorado, and its fossil lacks the features needed for comparison. A proposal to make D. carnegii the type species was rejected by the International Commission on Zoological Nomenclature, so D. longus remains the type species. Diplodocus lacustris was named in 1884 from a snout found at Morrison, Colorado, but in 2015 scientists said the snout belonged to Camarasaurus, so this name is also doubtful. Diplodocus hayi was named by William Jacob Holland in 1924 from a skull and partial skeleton (HMNS 175) found near Sheridan, Wyoming. In 2015 it was given its own genus, Galeamopus.

Paleobiology

Because so many skeleton remains have been found, Diplodocus is one of the best-studied dinosaurs. Its lifestyle has been the subject of many theories. Comparisons of its scleral rings with modern birds and reptiles suggest it may have been cathemeral, active throughout the day in short bursts. It is estimated to have walked at about 1.24 meters per second. Early scientists thought large sauropods lived in water, but a 1951 study by Kenneth A. Kermack suggested they could not have breathed through their nostrils while underwater. Since the 1970s, most scientists have agreed that sauropods lived on land and ate trees, ferns, and bushes. Scientists have debated how sauropods breathed with their large bodies and long necks, which added dead space. They likely had an avian respiratory system, which is more efficient than a mammalian or reptilian system, and the neck and chest of Diplodocus show great pneumaticity.

Further information: Sauropod neck posture

The idea of how Diplodocus stood has changed over the years. A 1910 reconstruction by Oliver P. Hay showed it with sprawling, lizard-like legs, a view supported by Gustav Tornier. William Jacob Holland challenged this, and footprints found in the 1930s eventually ended Hay's theory. Later, diplodocids were often shown with their necks held high, but studies of sauropod necks suggest the neck was close to horizontal. A nuchal ligament may have helped hold it in that position. A 2009 study argued that tetrapods hold the base of their necks upright when alert, and that Diplodocus may have held its neck at a higher angle than earlier studies concluded. A 1992 Columbia University study suggested the longest necks would have needed a very large heart, which led some to propose that small extra "hearts" in the neck pumped blood upward.

Diplodocine teeth were unusual, with long, slender crowns and wear on the cheek side. This suggests Diplodocus most likely fed by stripping leaves from branches with one row of teeth while the other guided them. A study by Young et al. (2012) found that bark-stripping would have put extreme stress on the skull, but branch-stripping was plausible. Its teeth were replaced regularly, usually in less than 35 days, and it appears to have eaten different plants than Camarasaurus. Its center of mass was close to its hip socket, so it could rear up on its hind legs and use its tail as a prop to reach higher leaves. Studies of its dental microwear suggest it ate softer foods than Camarasaurus. Its growth was once thought to be very fast, with adults reached at just over a decade, but a 2024 study estimated that one specimen, D. hallorum, was around 60 years old when it died, making it one of the oldest known dinosaur specimens.

Paleoenvironment

The Morrison Formation is a layer of rock made of sediments from shallow seas and rivers. Radiometric dating shows it is between 156.3 million years old (Ma) at its base and 146.8 million years old at its top. This places it in the late Oxfordian, Kimmeridgian, and early Tithonian ages of the Late Jurassic epoch. The area is thought to have been a semi-arid environment with wet and dry seasons. The Morrison Basin, where many dinosaurs lived, stretched from New Mexico to Alberta and Saskatchewan. It formed as the Front Range of the Rocky Mountains began to rise to the west. Sediments from its east-facing drainage basins were carried by streams and rivers and settled in swampy lowlands, lakes, river channels, and floodplains. The formation is similar in age to the Lourinha Formation in Portugal and the Tendaguru Formation in Tanzania.

The Morrison Formation shows a time dominated by huge sauropod dinosaurs. Dinosaurs found there include the theropods Ceratosaurus, Koparion, Stokesosaurus, Ornitholestes, Allosaurus, and Torvosaurus, the sauropods Brontosaurus, Apatosaurus, Brachiosaurus, and Camarasaurus, and the ornithischians Camptosaurus, Dryosaurus, Othnielia, Gargoyleosaurus, and Stegosaurus. Diplodocus is often found at the same sites as Apatosaurus, Allosaurus, Camarasaurus, and Stegosaurus. Allosaurus made up 70 to 75% of theropod specimens and was at the top trophic level of the Morrison food web. Many Morrison dinosaurs belong to the same genera as those in the Lourinha Formation in Portugal, or have close counterparts there, such as Brachiosaurus and Lusotitan, and Camptosaurus and Draconyx. Other animals included ray-finned fishes, frogs, salamanders, turtles like Dorsetochelys, sphenodonts, lizards, crocodile relatives such as Hoplosuchus, and several pterosaur species like Harpactognathus and Mesadactylus. Shells of bivalves and snails are also common. Plants included green algae, fungi, mosses, horsetails, cycads, ginkgoes, and several families of conifers. Vegetation ranged from forests of tree ferns and ferns along rivers (gallery forests) to fern savannas with a few trees, such as the Araucaria-like conifer Brachyphyllum.

Cultural significance

Diplodocus has been shown in more places than any other sauropod dinosaur. This may be because many of its skeletons have been found, and because it was once the longest dinosaur discovered. The first cast of D. carnegii, nicknamed "Dippy", is at the Natural History Museum, London. Other casts are at the National Museum of Natural History, Paris, the Museum für Naturkunde, Berlin, and the Museo de La Plata. Industrialist Andrew Carnegie gave many mounted casts of "Dippy" to rulers around the world at the start of the 20th century, which helped people everywhere get to know it. Casts are still on display in many museums, including D. carnegii in several of them.

The project drew much public attention in Europe, partly because of its link to 'big science', philanthropism, and capitalism. The German satirical weekly Kladderadatsch wrote a poem about the dinosaur:

In French, "Le diplodocus" became a general word for sauropods, much as "brontosaur" is in English. A skeleton of D. longus, made from several specimens and donated in 1907 by the American Museum of Natural History, is shown at the Senckenberg Museum in Frankfurt, Germany. A mounted skeleton of D. hallorum is at the New Mexico Museum of Natural History and Science. A war machine from World War I called the Boirault machine was designed in 1915. It was later judged impractical and nicknamed "Diplodocus militaris".