Diplodocus

Diplodocus was 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. They come from the Late Jurassic period.

The first Diplodocus fossils were found 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." This describes the double-beamed chevron bones on the underside of its tail. At the time, people thought these bones were unique.

Diplodocus lived in what is now middle-western North America, near the end of the Jurassic period. Its fossils are some of the more common dinosaur fossils found in the middle to upper Morrison Formation. Most of them come from rocks about 151 to 149 million years old, from the late Kimmeridgian Age. It may also have lived into the Tithonian. At least one specimen (AMNH FR 223) may come from some of the youngest rocks of the formation.

The Morrison Formation was a time and place where huge sauropod dinosaurs lived. These included Apatosaurus, Barosaurus, Brachiosaurus, Brontosaurus, and Camarasaurus. Diplodocus's great size may have helped it stay safe from the meat-eating dinosaurs Allosaurus and Ceratosaurus. Remains of these meat-eaters have been found in the same rock layers. This suggests that they lived at the same time as Diplodocus.

Description

Diplodocus was one of the best-known sauropods. These were very large animals with long necks and long, whip-like tails. They walked on four legs (quadrupedal). Their front legs were slightly shorter than their back legs, so their bodies were mostly flat. Their skeletons have been compared to cantilever bridges. D. carnegii is one of the longest dinosaurs known from a complete skeleton. It was 24 to 26 meters (79 to 85 ft) long. No skull has been confidently identified as belonging to Diplodocus. However, skulls of close relatives, such as Galeamopus, are well known. They were very small compared to the size of the animals. Diplodocus had small, peg-like teeth. The teeth pointed forward and were only at the front of the jaws. D. hallorum is known from partial remains. It was even larger, about the size of four elephants. Scientists have changed their size estimates over time as they studied the fossils more closely. The tail was about 55% of the animal's total body length. It was made of about 80 tail bones. Some scientists think the tail may have worked like a bullwhip or a coachwhip.

The middle of the tail had unusual "double beam" bones on its underside. These bones gave Diplodocus its name. At first, scientists thought only Diplodocus had these bones. Later, similar bones were found in other diplodocid dinosaurs and in Mamenchisaurus. The front feet were arranged in a column, and most toes had no claws. Some diplodocids had narrow, pointed spines on their skin, similar to those of an iguana. These spines may have run along the tail and possibly along the back and neck, like some hadrosaurids. Fossilized skin from the Mother's Day Quarry shows many different scale shapes. Some of these scales look like those around the legs 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 find was very incomplete. It was sent to the Yale Peabody Museum. In 1878, the paleontologist Othniel Charles Marsh named it Diplodocus longus, which means 'long double-beam'. Marsh was part of the Bone Wars, a contest with Edward Drinker Cope to find and describe as many kinds of fossils as possible. Later scientists found that this first find was doubtful. A request to the International Commission on Zoological Nomenclature suggested using D. carnegii as the new main species. The commission said no, so D. longus stayed the main species. More fossils were found at the same quarry from 1877 to 1884. These included a complete skull, found in 1883 and sent to the National Museum of Natural History.

After the Bone Wars, large 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 teams west to look for the most complete sauropod. In 1897, the American Museum's team found a partial skeleton at Como Bluff. It was collected by Barnum Brown and Henry Osborn. Later work on Diplodocidae showed that it belonged to the species D. hallorum. In 1899, a team paid for by Andrew Carnegie found a large, well-preserved Diplodocus skeleton in the Morrison Formation at Sheep Creek, Wyoming. Other dinosaurs were found there too, including Stegosaurus, Brontosaurus parvus, and Camarasaurus. In 1900, a second Carnegie team, led by John Bell Hatcher, William Jacob Holland, and Charles Gilmore, found another skeleton nearby. Hatcher named the 1899 skeleton Diplodocus carnegii in honor of Carnegie. By 1907, the Carnegie Museum had built a full display skeleton, nicknamed "Dippy." Copies were sent to museums in London, Berlin, Paris, Vienna, Bologna, St. Petersburg, Buenos Aires, Madrid, and Mexico City. The London copy was requested by King Edward VII. It 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. The rocks there date to the Kimmeridgian age of the Morrison Formation. Digging there went on until 1922, and many dinosaurs were uncovered. Several Diplodocus skulls were found there in 1912, 1915, and 1923. Holland described them in 1924. In 1923, the National Museum of Natural History collected a nearly complete Diplodocus skeleton from the same area. Gilmore described it in 1932. The Denver Museum of Nature and Science later got another specimen from the Carnegie Museum. It was also found at the Monument.

Few Diplodocus fossils were found for many years. In 1979, three hikers in New Mexico noticed bones stuck in stone near some petroglyphs, west of San Ysidro, New Mexico. The find was reported to the New Mexican Museum of Natural History. An expedition led by David D. Gillette collected it between 1985 and 1990. The specimen included 230 gastroliths, which are stones that some dinosaurs swallowed to help them digest food. It 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. The Cincinnati Museum of Natural History and Science dug it up in 1996. The Bighorn Basin Paleontological Institute dug there again in 2017. The quarry had many Diplodocus bones from young and adult animals. These included skin impressions and pathologies, which are signs of injury or illness in bones. 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.

Diplodocus is the type genus of the Diplodocidae, a family that is named after it. Diplodocids were still very large, but they were much thinner than other big plant-eating dinosaurs such as titanosaurs and brachiosaurs. They all had long necks and tails, and their bodies were held level with the ground. Their front legs were shorter than their back legs. They lived in the Late Jurassic period in 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 also a diplodocid, but it belongs to a 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. It is named after Jim and Ruth Hall of Ghost Ranch, and it was later given a new name 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. 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

Scientists have found many Diplodocus skeletons, so it is one of the best-studied dinosaurs. Its lifestyle has been the subject of many ideas. Its scleral rings are similar to those of modern birds and reptiles. This suggests it may have been cathemeral, meaning it was 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. 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 wondered how sauropods breathed with such large bodies and long necks, since the necks added dead space. They likely had an avian respiratory system, which works better than a mammalian or reptilian system. The neck and chest of Diplodocus also show a great deal of pneumaticity.

Further information: Sauropod neck posture

Scientists have changed their minds many times about how Diplodocus stood. A 1910 reconstruction by Oliver P. Hay showed it with sprawling, lizard-like legs, and Gustav Tornier agreed. William Jacob Holland disagreed, and footprints found in the 1930s finally ended Hay's idea. Later, diplodocids were often shown with their necks held high. However, 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 they are alert. It suggested Diplodocus may have held its neck at a higher angle than earlier studies had concluded. A 1992 study from Columbia University said the longest necks would have needed a very large heart. Some scientists proposed that small extra "hearts" in the neck could have helped pump blood upward.

Diplodocus had unusual teeth. They were long and slender, and they were worn on the cheek side. This suggests it most likely fed by stripping leaves from branches. One row of teeth pulled the leaves off while the other row guided them. A study by Young et al. (2012) found that stripping bark would have put extreme stress on the skull. Stripping branches, however, was possible. Its teeth were replaced regularly, usually in less than 35 days. It also seems to have eaten different plants than Camarasaurus. Its center of mass was close to its hip socket. This means it could rear up on its back legs and use its tail as a prop to reach higher leaves. Studies of its dental microwear suggest it ate softer foods than Camarasaurus. People once thought it grew very fast, reaching adulthood at just over a decade. However, a 2024 study estimated that one specimen, D. hallorum, was around 60 years old when it died. This makes it one of the oldest known dinosaur specimens.

Paleoenvironment

The Morrison Formation is a layer of rock made from mud, sand, and other material left by shallow seas and rivers. Radiometric dating shows it is between 156.3 million years old (Ma) at its bottom 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 land was probably a semi-arid place 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. Streams and rivers carried material from drainage basins on the east side and left it in swampy lowlands, lakes, river channels, and floodplains. The formation is about the same age as the Lourinha Formation in Portugal and the Tendaguru Formation in Tanzania.

The Morrison Formation was a time when huge sauropod dinosaurs were common. Dinosaurs found there include the meat-eating theropods Ceratosaurus, Koparion, Stokesosaurus, Ornitholestes, Allosaurus, and Torvosaurus. The sauropods included Brontosaurus, Apatosaurus, Brachiosaurus, and Camarasaurus. The plant-eating ornithischians included Camptosaurus, Dryosaurus, Othnielia, Gargoyleosaurus, and Stegosaurus. Diplodocus is often found at the same sites as Apatosaurus, Allosaurus, Camarasaurus, and Stegosaurus. Allosaurus was the most common meat-eater and sat at the top of the food web in the Morrison area, as a top trophic level animal. Many Morrison dinosaurs belong to the same groups as those in the Lourinha Formation in Portugal, or have close relatives 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. Plant life 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 ever 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. At the start of the 20th century, the industrialist Andrew Carnegie gave many copies of "Dippy" to rulers around the world. This helped people everywhere learn about the dinosaur. Casts are still on display in many museums, including several that show D. carnegii.

The project drew a lot of public attention in Europe. This was 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 like "brontosaur" is in English. A skeleton of D. longus, made from several specimens, was donated in 1907 by the American Museum of Natural History. It 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. During World War I, a war machine called the Boirault machine was designed in 1915. It was later judged impractical and nicknamed "Diplodocus militaris".