Diplodocus

*Diplodocus longus*

* Jurassic Park Institute Artwork
* Robert F Walters Artwork

**Diplodocus** (meaning double beam) was a species of diplodocid sauropod dinosaur that lived in western North America during the late Jurassic period, 154 to 150 million years ago. It is the longest dinosaur known from decent remains, although it is often thought that the longest species, *Diplodocus hallorum*, is usually called by the synonym *Seismosaurus*. It had a long tail, very similar to a bullwhip. It also had a narrow, shallow head, which is an identifying feature in the *Land Before Time* films and episodes but was not so much in real life, and one sharp claw on each front foot.

## Description

One of the best-known sauropods, *Diplodocus* was a large long-necked four-legged animal, with a long, whip-like tail. Its front limbs were a bit shorter than its hind limbs, which forms a horizontal stance for the most part. The long-necked, long-tailed animal with four sturdy legs has been mechanically compared with a suspension bridge. In fact, *Diplodocus* is the longest dinosaur known from a complete skeleton. Diplodocus species ranged from 80–115 ft, and weighed 10-16 metric tons.

    The skull of *Diplodocus* was very small, compared with the size of the animal, which could reach up to 115 ft, of which over 20 ft was neck. *Diplodocus* had small, 'peg'-like teeth that pointed forward and were only found in the front of the jaws. The neck was formed by at least 15 vertebrae and is now believed to have been held parallel to the ground most of the time and unable to have been raised much past horizontal.

*Diplodocus* had an 8 m long neck and a short 6 ft head. Its 14 m long tail had 80 vertebrae, and might have been used like a whip either to attack predators  or to make whip-cracking noises. The tail may have served as a counterbalance for the neck. The tail vertebrae had double beams (hence the name *Diplodocus*: double beam) that may have protected the blood vessels from being crushed if the tail pressed against the ground.

Like most sauropods, the front "feet" of *Diplodocus* were highly modified, with the finger and hand bones arranged upright, horseshoe-shaped in cross section. Diplodocus lacked claws on all but one toe of the front limb, and this claw was strangely large compared to other sauropods, flat from side to side, and detached from the bones of the hand. The role of this odd skilled claw is not known.

## History

Several species of *Diplodocus* were described from 1878 and 1924. The first skeleton was found at Cañon City, Colorado by Benjamin Mudge and Samuel Wendell Williston in 1877, and was named Diplodocus longus ('long double-beam'), by paleontologist Othniel Charles Marsh in 1878. *Diplodocus* remains have since been found in the Morrison Formation of the U.S. States of Colorado, Utah, Montana and Wyoming. Fossils of this animal are common, except for the skull. Although not the type species, D. carnegii is the best known and most famous due to the large number of casts of its skeleton in museums around the world.

The two Morrison Formation sauropod genera *Diplodocus* and *Barosaurus* had very similar limb bones. In the past, many isolated limb bones were automatically attributed to *Diplodocus* but may, in fact, have belonged to *Barosaurus*.

### Valid species

* ***D. longus***, the type species, is known from two skulls and some tail bones from the Morrison Formation of Colorado and Utah
* ***D. carnegii*** (also spelled *D. carnegiei*), named after Andrew Carnegie, is the best known, due to a near-complete skeleton collected by Jacob Wortman, of the Carnegie Museum of Natural History in Pittsburgh, Pennsylvania and described and named by John Bell Hatcher in 1901.
* ***D. hallorum***, best known as *Seismosaurus hallorum*. In 2004, a presentation at the annual conference of the Geological Society of America showed that *Seismosaurus* was in fact a species of *Diplodocus*. This was followed by a much more detailed publication in 2006, which not only renamed the species *Diplodocus hallorum*, but also speculated that it could prove to be the same as *D. longus*. The position that *D. hallorum* should be regarded as a specimen of *D. longus* was also taken by the authors of a new description of Supersaurus, refuting a previous hypothesis that *Seismosaurus* and *Supersaurus* were the same. It is now believed to be from an immature animal, not a separate species

### Doubtful species

* ***D. lacustris***, named by Marsh in 1884, from remains of a small animal from Morrison, Colorado.

## Classification

Diplodocus is the type genus of Diplodocidae. Members of this family, while still of great size, have a thinner build than other sauropods, such as the titanosaurs and brachiosaurs. All are marked by long necks and tails and a horizontal stance, with front legs shorter than the back legs. Diplodocids ruled North America and possibly Africa in the Late Jurassic.

A subfamily, Diplodocinae, was built to include *Diplodocus and* its kin, including *Barosaurus*. More distantly related is the co-existing *Apatosaurus*, which is still considered a diplodocid though not a diplodocine, as it is a member of the subfamily Apatosaurinae. *Dinheirosaurus* and *Tornieria* have also been identified as close relatives of ' Diplodocus *by some authors.*

The Diplodocoidea includes the diplodocids, as well as dicraeosaurids, rebbachisaurids, *Suuwassea*, *Amphicoelias*, and possibly *Haplocanthosaurus*, and/or the nemegtosaurids. This clade is the sister group to, *Camarasaurus*, brachiosaurids and titanosaurians; the Macronaria.

## Paleobiology

### Posture

The depiction of *Diplodocus* posture has changed considerably over the years. For instance, a classic 1910 reconstruction by Oliver P. Hay depicts two *Diplodocus* with splayed lizard-like limbs on the banks of a river. Hay argued that *Diplodocus* had a sprawling, lizard-like gait with widely splayed legs, and was supported by Gustav Tornier. However, this hypothesis was challenged by W. J. Holland, who showed that a sprawling *Diplodocus* would have needed a trench to pull its belly through.

Later, diplodocids were often portrayed with their necks held high up in the air, letting them graze from tall trees. Studies with computer models have shown that neutral pose of the neck was horizontal, not vertical. Scientists such as Kent Stephens have used this to argue that sauropods like *Diplodocus* did not raise their heads much past shoulder level, but studies to come showed that all tetrapods seem to hold their necks at the maximum possible vertical extension when in a normal, alert posture, and argued that the same would hold true for sauropods with unknown, unique traits that set the soft tissue form of their necks apart from other animals. One of the sauropod models was *Diplodocus*, which they found would have held its neck at about a 45 degree angle with the head pointed down in a resting pose.

As with the *Barosaurus*, the long neck of *Diplodocus* is the source of much controversy among scientists. A 1992 Columbia University study of Diplodocid neck structure indicated that the such long necks would have required a 1.6 ton heart. The study proposed that animals like these would have had rudimentary auxiliary 'hearts' in their necks, whose sole purpose was to pump blood up to the next 'heart'.

While the long neck has traditionally been seen as a feeding adaptation, it was suggested  that the oversized neck of *Diplodocus* and its relatives may have been primarily a sexual display, and feeding benefits would come nest, but a recent study refuted this idea in detail.

### Food

*Diplodocus* has strange teeth compared to other sauropods. The crowns are long and thin, egg-shaped in cross-section, while the top forms a blunt triangular point. The most prominent wear facet is on the apex, though unlike all other wear patterns seen in sauropods, *Diplodocus* wear patterns are on the cheek of both the top and bottom teeth. What this means is *Diplodocus* and other diplodocids had a radically different feeding mechanism than other sauropods. Branch stripping with one side of the mouth is the most likely feeding behavior of *Diplodocus*, as it explains the strange wear patterns of the teeth (from tooth–food contact). To strip a branch with one side of the mouth, one tooth row would have been used to strip leaves from the stem, while the other would act as a guide and stabilizer. With the long part of the skull in front of the eyes, it could strip a lot more stems in one move. The backwards motion of the lower jaws could have contributed two useful roles to feeding behaviour: 1) an increased gape, and 2) allowed fine adjustments of the relative positions of the tooth rows, creating a smooth stripping action.

With a flexible neck, and the option to use its tail and rear up on its hind limbs, *Diplodocus* would have had the ability to browse at many levels (low, medium, and high), up to 33 ft from the ground. The neck's range of movement may have let *Diplodocus* graze on submerged water plants, from riverbanks. This concept is backed up by the lengths of front and hind limbs. Plus, its peg-like teeth may have been used to eat soft water plants.

### Other anatomical

The head of *Diplodocus* has been widely shown with the nostrils on top due to the position of the nasal openings at the apex of the skull. There has been speculation to whether such a setup meant that *Diplodocus* may have had a trunk. A new study  said there was no evidence for a trunk. It noted that the facial nerve in an animal with a trunk, such as an elephant, is large as it supplies the trunk. The suggests that the facial nerve is too small in *Diplodocus*. Studies by Lawrence Witmer (2001) indicated that, while the nasal openings were high on the head, the actual, fleshy nostrils were much lower down on the snout.

Recent findings have shown that *Diplodocus* and other diplodocids may have had thin, pointed spines on their back, much like those on an iguana. This radically different look has been built in recent reconstructions, like *Walking with Dinosaurs*. It's not known just how many diplodocids had this trait, and if it was there in other sauropods.

### Reproduction and Growth

While there is no proof for *Diplodocus* nesting habits, other sauropods such as the titanosaurian *Saltasaurus* have been linked with nesting sites. The titanosaurian nesting sites show that may have laid their eggs communally over a large area in a lot of shallow pits, each covered with plants. It is possible that *Diplodocus* may have done the same.

*Diplodocus*, as well as other sauropods, grew at a fast rate, and reached sexual maturity in just a decade, though they kept growing through their lives. It was once thought that sauropods would grow slowly through their life, taking decades to reach maturity.

## JPInstitute.com Description

Diplodocus is a very famous giant Jurassic plant-eater. It was a huge, long-necked dinosaur, almost 100 feet long! In fact, it is the longest complete dinosaur skeleton ever discovered. Since its hind legs were longer than its front legs, this tells us that Diplodocus probably ate plants that were low to the ground. It was so big, however, that it could push trees over in order to get the leaves at the top down to the ground! It would probably stand on its hind legs to push, but it could not hold that pose for very long.

Philanthropist Andrew Carnegie had a lot to do with making dinosaurs popular and, in particular, the Diplodocus. The team of scientists who discovered this huge creature was working for Carnegie when they made the discovery. Carnegie was so amazed at the size of the dinosaur that he had copies made and sent to 11 museums around the world. This helped make many millions of people aware of this great creature.

Diplodocus is the namesake of the diplodocid family - long neck, pillar like legs, long tapering tail and enormous size. It had, like the other family members, peg-like teeth in an elongated head that seemed very small for such a large creature. There is much speculation about how much these creatures needed to eat and how such a small head could ingest enough food to fuel such a large body. Some scientists have stated that these huge, small-headed creatures would have needed to eat every waking moment in order to provide enough food to keep such a large body alive.

Like many other large sauropods, Diplodocus probably swallowed stones which it kept in a gizzard similar to that found in a chicken to facilitate digesting food. The tough plant fibers would spend time in the gizzard stewing and being ground up by the stones. There is some speculation about the use of the very long tail of Diplodocus and other members of its family. If it was used as a weapon, it would be very deadly. Because of its length, the speed at the tip, if swung forcefully, would have been very high, possibly faster than the speed of sound.

## Links

http://web.archive.org/web/20040214163251fw\_/http://www.jpinstitute.com/dinopedia/dinocards/dc\_diplo.html

## References

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