Old Earth Ministries Online Dinosaur Curriculum

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Lesson 42 - Diplodocus, Part 2

Paleobiology

Due to a wealth of skeletal remains, Diplodocus is one of the best-studied dinosaurs. Many aspects of its lifestyle have been subjects of various theories over the years.

Habitat

Marsh and then Hatcher assumed the animal was aquatic, because of the position of its nasal openings at the apex of the cranium. Similar aquatic behavior was commonly depicted for other large sauropods such as Brachiosaurus and Apatosaurus. However, 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. Since the 1970s, general consensus has the sauropods as firmly terrestrial animals, browsing on trees, ferns and bushes.

Diplodocus

Quick Facts

 

Length:  up to 115 feet

Weight:   up to 35,000 lbs

Date Range:   154 - 150 Ma, Jurassic Period

 

Diplodocus

 Mounted D. carnegii skeleton cast, Berlin Hauptbahnhof (Picture Source)

 

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 contested by W. J. Holland, who demonstrated that a sprawling Diplodocus would have needed a trench to pull its belly through. Finds of sauropod footprints in the 1930s eventually put Hay's theory to rest.

Later, diplodocids were often portrayed with their necks held high up in the air, allowing them to graze from tall trees. Studies using computer models have shown that neutral posture of the neck was horizontal, rather than vertical, and scientists such as Kent Stephens have used this to argue that sauropods including Diplodocus did not raise their heads much above shoulder level. However, subsequent studies demonstrated that all tetrapods appear 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 barring any unknown, unique characteristics that set the soft tissue anatomy of their necks apart from other animals. One of the sauropod models in this study was Diplodocus, which they found would have held its neck at about a 45 degree angle with the head pointed downwards in a resting posture.

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

While the long neck has traditionally been interpreted as a feeding adaptation, a recent study suggests that the oversized neck of Diplodocus and its relatives may have been primarily a sexual display, with any other feeding benefits coming second.

Diet

Diplodocus has highly unusual teeth compared to other sauropods. The crowns are long
Diplodocus
The original D. carnegii (foreground) at the Carnegie Museum  (Picture Source
 and slender, elliptical in cross-section, while the apex forms a blunt triangular point. The most prominent wear facet is on the apex, though unlike all other wear patterns observed within sauropods, Diplodocus wear patterns are on the labial (cheek) side of both the upper and lower teeth. What this means is Diplodocus and other diplodocids had a radically different feeding mechanism than other sauropods. Unilateral branch-stripping is the most likely feeding behavior of Diplodocus, as it explains the unusual wear patterns of the teeth (coming from tooth-food contact). In unilateral branch stripping, one tooth row would have been used to strip foliage from the stem, while the other would act as a guide and stabilizer. With the elongated preorbital (in front of the eyes) region of the skull, longer portions of stems could be stripped in a single action. Also the palinal (backwards) motion of the lower jaws could have contributed two significant 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 laterally and dorsoventrally flexible neck, and the possibility of using its tail and rearing up on its hind limbs (tripodal ability), Diplodocus would have had the ability to browse at many levels (low, medium, and high), up to approximately 10 metres (33 ft) from the ground. The neck's range of movement would have also allowed the head to graze below the level of the body, leading some scientists to speculate on whether Diplodocus grazed on submerged water plants, from riverbanks. This concept of the feeding posture is supported by the relative lengths of front and hind limbs. Furthermore, its peglike teeth may have been used for eating soft water plants.

In 2010, Whitlock et al. described a juvenile skull of Diplodocus (CM 11255) that differs greatly from adult skulls of the same genus: its snout is not blunt, and the teeth are not confined to the front of the snout. These differences suggest that adults and juveniles were feeding differently. Such an ecological difference between adults and juveniles had not been previously observed in sauropodomorphs.

Other anatomical aspects

The head of Diplodocus has been widely depicted with the nostrils on top due to the
Diplodocus head
a) skull, b) classic rendering of the head with nostrils on top, c) with speculative trunk, d) modern depiction with nostrils low on the snout and a possible resonating chamber  (Picture Source
 position of the nasal openings at the apex of the skull. There has been speculation over whether such a configuration meant that Diplodocus may have had a trunk. A recent study surmised there was no paleoneuroanatomical evidence for a trunk. It noted that the facial nerve in an animal with a trunk, such as an elephant, is large as it innervates the trunk. The evidence suggests that the facial nerve is very small in Diplodocus. Studies by Lawrence Witmer (2001) indicated that, while the nasal openings were high on the head, the actual, fleshy nostrils were situated much lower down on the snout.

Recent discoveries have suggested that Diplodocus and other diplodocids may have had narrow, pointed keratinous spines lining their back, much like those on an iguana. This radically different look has been incorporated into recent reconstructions, notably Walking with Dinosaurs. It is unknown exactly how many diplodocids had this trait, and whether it was present in other sauropods.

Reproduction and growth

While there is no evidence for Diplodocus nesting habits, other sauropods such as the titanosaurian Saltasaurus have been associated with nesting sites. The titanosaurian nesting sites indicate that may have laid their eggs communally over a large area in many shallow pits, each covered with vegetation. It is possible that Diplodocus may have done the same. The documentary Walking with Dinosaurs portrayed a mother Diplodocus using an ovipositor to lay eggs, but it was pure speculation on the part of the documentary.

Following a number of bone histology studies, Diplodocus, along with other sauropods, grew at a very fast rate, reaching sexual maturity at just over a decade, though continuing to grow throughout their lives. Previous thinking held that sauropods would keep growing slowly throughout their lifetime, taking decades to reach maturity.

Classification

Diplodocus is both the type genus of, and gives its name to Diplodocidae, the family to which it belongs. Members of this family, while still massive, are of a markedly more slender build when compared with other sauropods, such as the titanosaurs and brachiosaurs. All are characterised by long necks and tails and a horizontal posture, with forelimbs shorter than hindlimbs. Diplodocids flourished in the Late Jurassic of North America and possibly Africa and appear to have been replaced ecologically by titanosaurs during the Cretaceous.

In popular culture

Diplodocus has been a famous and much-depicted dinosaur as it has been on display in more places than any other sauropod dinosaur. Much of this has probably been due to its wealth of skeletal remains and former status as the longest dinosaur. However, the donation of many mounted skeletal casts by industrialist Andrew Carnegie to potentates around the world at the beginning of the twentieth century did much to familiarize it to people worldwide. Casts of Diplodocus skeletons are still displayed in many museums worldwide, including an unusual D. hayi in the Houston Museum of Natural Science, and D. carnegii in a number of institutions.

Diplodocus has been a frequent subject in dinosaur films, both factual and fictional. It was featured in the second episode of the award-winning BBC television series Walking with Dinosaurs. The episode "Time of the Titans" follows the life of a simulated Diplodocus 152 million years ago. In literature, James A. Michener's book Centennial has a chapter devoted to Diplodocus, narrating the life and death of one individual.

Diplodocus is a commonly seen figure in dinosaur toy and scale model lines. It has had two figures in the Carnegie Collection.

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