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Diplodocus

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Diplodocus
Temporal range: Late Jurassic
Diplodocus skull
Fossil
Scientific classification
Kingdom:
Animalia
Phylum:
Chordata
Class:
Sauropsida
Superorder:
Dinosauria
Order:
Saurischia
Suborder:
Sauropodomorpha
Infraorder:
Sauropoda
Family:
Diplodocidae
Genus:
Diplodocus

Marsh, 1878
Species
  • D. longus (type)
  • D. carnegiei Hatcher, 1901
  • D. hayi Holland, 1924
  • D. hallorum (Gillette, 1991) Lucas et al., 2006
Synonyms
  • Seismosaurus Gillette, 1991

Diplodocus (pronounced /ˌdɪploʊˈdoʊkəs/ or /dɪˈplɔdəkəs/) is a genus of diplodocid sauropod dinosaur whose fossilised skeleton was first discovered in 1878. The generic name refers to its double-beamed chevron bones (Greek diplos/διπλος meaning 'double' and dokos/δοκος meaning 'wooden beam' or 'bar') located in the underside of the tail.[1] They were initially believed to be unique to Diplodocus; however, they have since then been discovered in other diplodocids.

It lived in what is now western North America at the end of the Jurassic Period. Diplodocus was one of the more common dinosaurs found in the Upper Morrison Formation, about 150 to 147 million years ago, in what is now termed the Kimmeridgian and Tithonian stages. This was an environment and time dominated by gigantic sauropod dinosaurs such as Camarasaurus, Barosaurus, Apatosaurus and Brachiosaurus.[2]

Diplodocus is among the most easily identifiable dinosaurs, with its classic dinosaur shape, long neck and tail and four sturdy legs. For many years, it was the longest dinosaur known. 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 they coexisted with Diplodocus.

Description

Skeletal diagram, with humans for scale.

One of the best-known sauropods, Diplodocus was a very large long-necked quadrupedal animal, with a long, whip-like tail. Its forelimbs were slightly shorter than its hind limbs, resulting in a largely horizontal posture. The long-necked, long-tailed animal with four sturdy legs has been mechanically compared with a suspension bridge.[3] In fact, Diplodocus is the longest dinosaur known from a complete skeleton.[3] While dinosaurs such as Supersaurus were probably longer, fossil remains of these animals are only fragmentary.[4]

The skull of Diplodocus was very small, compared with the size of the animal, which could reach up to 27 metres (90 feet), of which 6 metres (20 feet) was neck.[5] Diplodocus had small, 'peg'-like teeth only at the anterior part of the jaws, which were distinctly procumbent.[6] Its braincase was small. The neck was composed of at least fifteen vertebrae and is now believed to have been generally held parallel to the ground and unable to have been elevated much past horizontal.[7]

Diplodocus tail, Natural History Museum, London.
Diplodocus - Caudal vertebrae in the tail.

Diplodocus had an extremely long tail, composed of about eighty caudal vertebrae,[8] which is almost double the number some of the earlier sauropods had in their tails (such as Shunosaurus with 43), and far more than contemporaneous macronarians had (such as Camarasaurus with 53). There has been speculation as to whether it may have had a defensive[9] or noisemaking function.[10] The tail may have served as a counterbalance for the neck. The middle part of the tail had 'double beams' (oddly-shaped bones on the underside, which gave Diplodocus its name). 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.

Discovery and species

Several species of Diplodocus were described between 1878 and 1924. The first skeleton was found at Como Bluff, Wyoming by Benjamin Mudge and Samuel Wendell Williston in 1878, and was named Diplodocus longus ('long double-beam'), by palaeontologist Othniel Charles Marsh in 1878.[11] Diplodocus remains have since been found in the Morrison Formation of the western U.S. States of Colorado, Utah, Montana and Wyoming. Fossils of this animal are common, except for the skull, which is often missing from otherwise complete skeletons. Although not the type species, D. carnegiei is the most completely 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.[12]

Valid species

Nomina dubia (Doubtful species)

  • D. lacustris is a nomen dubium, named by Marsh in 1884, from remains of a smaller animal from Morrison, Colorado.[17] These remains are now believed to have been from an immature animal, rather than from a separate species.[18]

Palaeobiology

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[19] 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. The idea of an aquatic existence was later debunked, as the water pressure on the chest wall of Diplodocus was proven to have been too great for the animal to have breathed. Since the 1970s, general consensus has the sauropods as firmly terrestrial animals, browsing on trees. However, a more recent theory suggests a likely riparian habitat for Diplodocus.

Posture

Current posture with horizontal neck, NHM, London.
Depiction of Diplodocus by Oliver P. Hay in 1910.[20]
Another classic depiction of Diplodocus by Mary Woodward (1905), with neck high up in the air and tail on the ground, a posture now generally believed to be incorrect.

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,[21] and was supported by Gustav Tornier. However, this hypothesis was put to rest by W. J. Holland, who demonstrated that a sprawling Diplodocus would have needed a trench to pull its belly through.[22]

Later, diplodocids were often portrayed with their necks held high up in the air, allowing them to graze from tall trees. More recently, scientists have argued that the heart would have had trouble sustaining sufficient blood pressure to oxygenate the brain. Furthermore, more recent studies have shown that the structure of the neck vertebrae would not have permitted the neck to bend far upwards.[23][24]

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. 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'.[3]

While the long neck has traditionally been interpreted as a feeding adaptation, a recent study[25] 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

Modern depiction of Diplodocus with horizontal neck, flexible whip tail, keratinous spines and nostrils low on the snout.

Diplodocus had highly unusual teeth compared to other sauropods. The crowns were long and slender, elliptical in cross-section, while the apex forms a blunt triangular point.[26] 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.[26] 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 behaviour of Diplodocus,[27][28][29] 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 stabiliser. With the elongated preorbital (in-front of the eyes) region of the skull, longer portions of stems could be stripped in a single action.[26] 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.[26]

With a laterally and dorsoventrally flexible neck, and the possibilty 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 (39 ft) from the ground.[30] 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.[23]

Other anatomical aspects

a) skull, b) classic rendering of the head with nostrils on top, c) Bakker's theory of a trunk, d) modern depiction with nostrils low on the snout and a possible resonating chamber.

The head of Diplodocus has been widely depicted with the nostrils on top due to the 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.[31] A recent study[32] 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.[33]

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.[34][35] 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.[36][37] 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.[38][39][40] 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.[17] 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[8] and appear to have been replaced ecologically by titanosaurs during the Cretaceous.

A subfamily, Diplodocinae, was erected to include Diplodocus and its closest relatives, including Barosaurus. More distantly related is the contemporaneous Apatosaurus, which is still considered a diplodocid although not a diplodocine, as it is a member of the subfamily Apatosaurinae.[41][42] The Portuguese Dinheirosaurus and the African Tornieria have also been identified as close relatives of Diplodocus by some authors.[43][44]

The Diplodocoidea comprises of the diplodocids, as well as dicraeosaurids, rebbachisaurids, Suuwassea,[41][42] Amphicoelias[44] and possibly Haplocanthosaurus,[45] and/or the nemegtosaurids.[5] This clade is the sister group to, Camarasaurus, brachiosaurids and titanosaurians; the Macronaria.[5][45] Together they comprise Neosauropoda; the largest, most diverse and successful group of sauropodomorph dinosaurs.

File:Diplodocus carnegii statue.jpg
A statue of Diplodocus carnegiei in Pittsburgh, Pennsylvania.

Diplodocus has been a famous and much-depicted 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 around the world a century ago did much to familarise 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. carnegiei in the Natural History Museum in London, the Natural Science Museum in Madrid, Spain, the Senckenberg Museum in Frankfurt, Germany, the Field Museum of Natural History in Chicago and, of course, the Carnegie Museum of Natural History in Pittsburgh. A mounted skeleton of D. longus is at the Smithsonian National Museum of Natural History in Washington, D. C., while a mounted skeleton of D. hallorum (formerly Seismosaurus), which may be the same as D. longus, can be found at the New Mexico Museum of Natural History and Science.

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. It had cameo appearances in The Land That Time Forgot and in The Lost World (2001), as well as the animated film The Land Before Time VI: The Secret of Saurus Rock, the character "Doc", presumably short for Diplodocus, voiced by Kris Kristofferson, was a Diplodocus; in contrast to the "long-neck" protagonists, which were Apatosaurus. The animated feature Fantasia features many sauropods in the Rite of Spring sequence, some narrower-headed ones of which may be Diplodocus.

Footnotes

  1. ^ Liddell & Scott (1980). Greek-English Lexicon, Abridged Edition. Oxford University Press, Oxford, UK. ISBN 0-19-910207-4.
  2. ^ Christine C.E. & Peterson, F. (2004). "Reconstruction of the Upper Jurassic Morrison Formation extinct ecosystem—a synthesis". Sedimentary Geology 167, 309–355
  3. ^ a b c Lambert D. (1993)The Ultimate Dinosaur Book ISBN 0-86438-417-3
  4. ^ Wedel, M.J. and Cifelli, R.L. Sauroposeidon: Oklahoma’s Native Giant. 2005. Oklahoma Geology Notes 65:2.
  5. ^ a b c Upchurch P, Barrett PM, Dodson P (2004). "Sauropoda". In Weishampel DB, Osmólska H, Dodson P (ed.). The Dinosauria (2nd Edition). University of California Press. p. 316. ISBN 0-520-24209-2.{{cite book}}: CS1 maint: multiple names: authors list (link)
  6. ^ Upchurch, P. & Barrett, P.M. (2000). Chapter 4: The evolution of sauropod feeding mechanism. IN: Evolution of Herbivory in Terrestrial Vertebrates ISBN 0-521-59449-9
  7. ^ Stevens, K.A. & Parrish, M. (1999). "Neck Posture and Feeding Habits of Two Jurassic Sauropod Dinosaurs". Science 284, 798-800
  8. ^ a b Wilson JA (2005). "Overview of Sauropod Phylogeny and Evolution". In Rogers KA & Wilson JA(eds) (ed.). The Sauropods:Evolution and Paleobiology. Indiana University Press. p. 15-49. ISBN 0-520-24623-3. {{cite book}}: |editor= has generic name (help)
  9. ^ Holland WJ (1915). "Heads and Tails: a few notes relating to the structure of sauropod dinosaurs". Annals of the Carnegie Museum. 9: 273–278. {{cite journal}}: Check date values in: |year= (help)CS1 maint: year (link)
  10. ^ Myhrvold NP and Currie PJ (1997). "Supersonic sauropods? Tail dynamics in the diplodocids". Paleobiology. 23: 393–409. {{cite journal}}: Check date values in: |year= (help)CS1 maint: year (link)
  11. ^ Marsh OC. Principal characters of American Jurassic dinosaurs. Part I. American Journal of Science 3; 411-416 (1878).
  12. ^ McIntosh (2005). "The Genus Barosaurus (Marsh)". In Carpenter, Kenneth and Tidswell, Virginia (ed.) (ed.). Thunder Lizards: The Sauropodomorph Dinosaurs. Indiana University Press. pp. 38–77. ISBN 0-253-34542-1. {{cite book}}: |editor= has generic name (help)CS1 maint: multiple names: editors list (link)
  13. ^ Upchurch P, Barrett PM, Dodson P (2004). "Sauropoda". In Weishampel DB, Osmólska H, Dodson P (ed.). The Dinosauria (2nd Edition). University of California Press. p. 305. ISBN 0-520-24209-2.{{cite book}}: CS1 maint: multiple names: authors list (link)
  14. ^ Holland WJ. The skull of Diplodocus. Memoirs of the Carnegie Museum IX; 379-403 (1924).
  15. ^ Reappraisal of Seismosaurus, A Late Jurassic Sauropod Dinosaur from New Mexico
  16. ^ Lucas, S.G., Spielman, J.A., Rinehart, L.A., Heckert, A.B., Herne, M.C., Hunt, A.P., Foster, J.R., and Sullivan, R.M. (2006). "Taxonomic status of Seismosaurus hallorum, a Late Jurassic sauropod dinosaur from New Mexico". In Foster, J.R., and Lucas, S.G. (ed.). Paleontology and Geology of the Upper Morrison Formation. New Mexico Museum of Natural History and Science (bulletin 36). pp. 149–161. ISSN 1524-4156.{{cite book}}: CS1 maint: multiple names: authors list (link)
  17. ^ a b Marsh, O.C. 1884. Principal characters of American Jurassic dinosaurs. Part VII. On the Diplodocidae, a new family of the Sauropoda. American Journal of Science 3: 160-168.
  18. ^ Upchurch, P., Barrett, P.M., and Dodson, P. (2004). "Sauropoda." In D. B. Weishampel, H. Osmólska, and P. Dodson (eds.), The Dinosauria (2nd edition). University of California Press, Berkeley 259-322.
  19. ^ Hatcher JB. "Diplodocus (Marsh): Its osteology, taxonomy, and probable habits, with a restoration of the skeleton,". Memoirs of the Carnegie Museum, vol. 1 (1901), pp. 1-63
  20. ^ Hay, O. P., 1910, Proceedings of the Washington Academy of Sciences, vol. 12,, pp. 1-25
  21. ^ Hay, Dr. Oliver P., "On the Habits and Pose of the Sauropod Dinosaurs, especially of Diplodocus." The American Naturalist, Vol. XLII, Oct. 1908
  22. ^ Holland, Dr. W. J., "A Review of Some Recent Criticisms of the Restorations of Sauropod Dinosaurs Existing in the Museums of the United States, with Special Reference to that of Diplodocus carnegiei in the Carnegie Museum", The American Naturalist, 44:259–283. 1910.
  23. ^ a b Stevens KA, Parrish JM (2005). "Neck Posture, Dentition and Feeding Strategies in Jurassic Sauropod Dinosaurs". In Carpenter, Kenneth and Tidswell, Virginia (ed.) (ed.). Thunder Lizards: The Sauropodomorph Dinosaurs. Indiana University Press. pp. 212–232. ISBN 0-253-34542-1. {{cite book}}: |editor= has generic name (help)CS1 maint: multiple names: editors list (link)
  24. ^ Upchurch, P; et al. (2000). ""Neck Posture of Sauropod Dinosaurs"" (PDF). Science 287, 547b (2000);DOI: 10.1126/science.287.5453.547b. Retrieved 2006-11-28. {{cite web}}: Explicit use of et al. in: |first= (help); Italic or bold markup not allowed in: |publisher= (help)
  25. ^ Senter,P. "Necks for Sex: Sexual Selection as an Explanation for Sauropod Neck Elongation". Journal of Zoology, 2006
  26. ^ a b c d Upchurch, P. & Barrett, P.M. (2000). Chapter 4: The evolution of sauropod feeding mechanism. IN: Evolution of Herbivory in Terrestrial Vertebrates ISBN 0-521-59449-9
  27. ^ Norman, D.B. (1985). "The illustrated Encyclopedia of Dinosaurs". London: Salamander Books Ltd
  28. ^ Dodson, P. (1990). Sauropod paleoecology. IN: "The Dinosauria" 1st Edition, (Eds. Weishampel, D.B., Dodson, P. & Osmólska, H.)
  29. ^ Barrett, P.M. & Upchurch, P. (1994). Feeding mechanisms of Diplodocus. Gaia 10, 195-204
  30. ^ Barrett, P.M. & Upchurch, P. (2005). Sauropodomorph Diversity through Time, Paleoecological and Macroevolutionary Implications. IN: "The Sauropods: Evolution and Paleobiology" (Eds. Curry, K. C.)
  31. ^ Bakker, Robert T. (1986) The Dinosaur Heresies: New Theories Unlocking the Mystery of the Dinosaurs and their Extinction. New York: Morrow.
  32. ^ Knoll, F., Galton, P.M., López-Antoñanzas, R. (2006). "Paleoneurological evidence against a proboscis in the sauropod dinosaur Diplodocus." Geobios, 39: 215-221
  33. ^ Lawrence M. Witmer et al., "Nostril Position in Dinosaurs and other Vertebrates and its Significance for Nasal Function." Science 293, 850 (2001)
  34. ^ Czerkas, S. A. (1993). "Discovery of dermal spines reveals a new look for sauropod dinosaurs." Geology 20, 1068-1070
  35. ^ Czerkas, S. A. (1994). "The history and interpretation of sauropod skin impressions." In Aspects of Sauropod Paleobiology (M. G. Lockley, V. F. dos Santos, C. A. Meyer, and A. P. Hunt, Eds.), Gaia No. 10. (Lisbon, Portugal).
  36. ^ Walking on Eggs: The Astonishing Discovery of Thousands of Dinosaur Eggs in the Badlands of Patagonia, by Luis Chiappe and Lowell Dingus. June 19, 2001, Scribner
  37. ^ Grellet-Tinner, Chiappe, & Coria, "Eggs of titanosaurid sauropods from the Upper Cretaceous of Auca Mahuevo (Argentina)", Can. J. Earth Sci. 41(8): 949-960 (2004)
  38. ^ Sander, P. M. (2000). "Long bone histology of the Tendaguru sauropods: Implications for growth and biology". Paleobiology 26, 466-488
  39. ^ Sander, P. M., N. Klein, E. Buffetaut, G. Cuny, V. Suteethorn, and J. Le Loeuff (2004). "Adaptive radiation in sauropod dinosaurs: Bone histology indicates rapid evolution of giant body size through acceleration". Organisms, Diversity & Evolution 4, 165-173
  40. ^ Sander, P. M., and N. Klein (2005). "Developmental plasticity in the life history of a prosauropod dinosaur". Science 310 1800-1802
  41. ^ a b Taylor, M.P. & Naish, D. 2005. The phylogenetic taxonomy of Diplodocoidea (Dinosauria: Sauropoda). PaleoBios 25(2): 1-7. (download here)
  42. ^ a b Harris, J.D. 2006. The significance of Suuwassea emiliae (Dinosauria: Sauropoda) for flagellicaudatan intrarelationships and evolution. Journal of Systematic Palaeontology 4(2): 185–198.
  43. ^ Bonaparte, J.F. & Mateus, O. 1999. A new diplodocid, Dinheirosaurus lourinhanensis gen. et sp. nov., from the Late Jurassic beds of Portugal. Revista del Museo Argentino de Ciencias Naturales. 5(2):13-29. (download here)
  44. ^ a b Rauhut, O.W.M., Remes, K., Fechner, R., Cladera, G., & Puerta, P. 2005. Discovery of a short-necked sauropod dinosaur from the Late Jurassic period of Patagonia. Nature 435: 670-672.
  45. ^ a b Wilson, J. A., 2002, "Sauropod dinosaur phylogeny: critique and cladistica analysis". Zoological Journal of the Linnean Society 136: 217-276.
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