Sauropod neck posture

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Diplodocus restored with an upright posture, based on comparison with living animals, from Taylor et al., 2009 Diplodocus habitual neck posture.jpeg
Diplodocus restored with an upright posture, based on comparison with living animals, from Taylor et al., 2009

Sauropod neck posture is a subject occasionally debated among scientists, with some favoring postures closer to horizontal whilst others a more upright posture. Research has looked at various avenues of evidence and analysis including: attempting to reconstruct the neutral posture of their necks and estimating range of motion by studying the bones; attempting to reconstruct sauropod metabolism and the energy requirements of sustaining incredibly long necks in various postures; and comparing sauropod neck anatomy to those of living animals. [1] [2]

Contents

Biomechanics

The biomechanics of sauropod skeletons and necks can help determine at what angle the neck was positioned. [3]

Flexibility

In 2013, a study led by Matthew J. Cobley and published in PLOS ONE focused on the flexibility of the necks of sauropods. They compared the necks of ostriches with sauropod genera to find out how flexible the necks really were. The study noted that previous biomechanics studies found the necks to have been positioned between the extremes of a vertical, and a downward slanted neck. In conclusion, the study found that sauropod neck flexibility should not be based on osteology alone, and if it is, the results should be used with caution. Even though there is a lack of preserved muscle tissue that would determine flexibility, sauropod necks were probably less flexible than previously thought. [4]

In 2014, Mike P. Taylor analysed the flexibility in the necks of Apatosaurus and Diplodocus . He found that Cobley et al. was incorrect in the fact that vertebrae imply the neck is less flexible than in actuality. Cobley et al. found necks to be much less flexible than in reality when cartilage was added. It was found that the cartilage between the joints would have allowed for the neck to flex far past 90°. However, Taylor noted that while the neck could flex above the vertical, the osteological neutral pose would have been around horizontal, with the habitual pose having the head held upwards in an alert pose. [5]

Muscling

Sauropod necks were probably highly muscled to suit their feeding level. Brachiosaurus brancai (now Giraffititan ) was probably a high browser, so it would have been more muscled along the neck than other sauropods like Diplodocus and Dicraeosaurus interpreted as low browsers. The tail and limb length of B. brancai would also need to be greater, to balance out the inclined neck. [6] However, the question of whether sauropods were endothermic or ectothermic plays a major part in how sauropods were muscled, as endotherms have particularly more intestines and stomach than ectotherms. The amount of gut needed could determine how much food was eaten by sauropods, and therefore at what elevation their heads were held. [7]

Heart and metabolic stress

The upright posture of sauropod necks is seen by some as requiring implausibly high blood pressure and heart strength. A 2000 study conducted by Roger Seymour and Harvey Lillywhite found that the blood pressure needed to reach the head with an upright neck would be 700 millimetres of mercury (28 inHg), interpreted as fatal to an endotherm, or highly dangerous to an ectotherm, even with adequate heart musculature. [2] A later study by Seymour concluded that it would have required half the animal's energy intake to pump the blood to the head. This would disfavor sauropods being high browsers, and instead having lower necks while feeding than commonly portrayed. [8]

The above work summarily dismisses the hypothesis of secondary hearts in the neck [9] as evolutionarily implausible, assuming arterial valves could have no role without associated musculature.

Hypotheses

Restored posture of Opisthocoelicaudia from the original description (A), and by Schwartz et al. (B) Opisthocoelicaudia posture.svg
Restored posture of Opisthocoelicaudia from the original description (A), and by Schwartz et al. (B)

A few hypotheses have been generated to solve the dispute over how sauropods held their necks. [1]

Horizontal pose

Kent Stevens and Michael Parrish have been the two main supporters of a horizontal neck posture. In 1999, they studied the genera Apatosaurus and Diplodocus , finding the habitual pose of the genera to be slightly declined. They claimed that both sauropods had necks much less flexible than previously thought, with the neck vertebrae of Diplodocus being more inflexible than Apatosaurus. Those two poses would suggest that the sauropods were ground feeders, instead of browsing off taller flora. [12] Later, in 2005, Stevens and Parrish studied the biomechanics of sauropod necks on a wider variety of sauropods, from the Jurassic: Apatosaurus, Diplodocus, Camarasaurus , Brachiosaurus , Dicraeosaurus , Cetiosaurus , and Euhelopus . All were stated to have a horizontal, or even declining neck. [13]

However, in 2009 multiple flaws were found with this argument. Michael P. Taylor et al. compared the neck posture of sauropods to that of extant reptiles and other tetrapods, finding these animals' habitual poses to be entirely different from the assumptions of Stevens and Parrish. The latters' errors come mainly from their preconceptions about animals' habitual pose in life, which they simply assumed would naturally match the Osteological Neutral Pose (or ONP). Taylor et al. find the ONP to be, not the actual habitual pose of any examined animal, but an arbitrarily chosen midpoint between the two structural extremes of bone placement. [1] ONP, then, is merely one place in the range of physically possible motion.

Incline pose

Another, more widely supported hypothesis about sauropod neck posture is that the necks were held at an incline, but not as upright as commonly shown. [1] Daniela Schwartz et al. in 2006 published a study of the scapula and coracoids, sometimes fused into scapulocoracoids, of sauropod genera. Previously, sauropod shoulder girdles were thought to have been positioned horizontally along the torso, but Schwartz et al. found that the girdles should not have been positioned horizontally, and instead, they would have been angled at an average of 55° to 65°. The study reconstructed the skeletons of Diplodocus, Camarasaurus, and the titanosaur Opisthocoelicaudia , all known from a complete shoulder girdle, with the correct orientation of the scapulocoracoids. For Diplodocus, a 60° shoulder blade would have meant that the neck was more-or-less horizontal, [11] not too much different from the horizontal pose. [12] [13] A juvenile Camarasaurus found by Gilmore was originally described as having the scapulocoracoid in "just the right place", but with it oriented at an angle of 45°, Schwartz et al. criticized the stance. The skeleton found by Schwartz et al. with the angle of the scapulocoracoid is similar to previous reconstruction of the genus by Osborn and Mook, and Jensen. Opisthocoelicaudia was found to have had two possibly poses, both with the scapulocoracoid angled at about 60°. No previous reconstructions, unlike with Camarasaurus, have restored Opisthocoelicaudia similarly. [11]

Upright pose for some sauropods

Despite skepticism, Euhelopus and Brachiosaurus have been found on anatomical evidence to have held their necks at a vertical angle, which has been treated as impossible for sauropods. Studies have concluded that the blood pressure and energy spent holding necks erect would have been too great to survive; yet Euhelopus and Brachiosaurus, at least, did so anyhow. The energy spent by pumping blood to the head is interpreted as too great for most sauropods, but when they travel often, which has been suggested for those two genera, it would have actually saved energy. The biomechanical evidence favours an upright neck when travelling to spread apart resources. The study finding this conclusion also tested how much energy would have been expended when walking 100 m (330 ft) and standing, both with an upright neck. The approximate conclusion was that an about equal amount of energy would have been used up. Elongated cervical ribs are skeletal evidence for a strong core to support the neck and limit its movement when walking. The study supports the idea that during times of drought and famine, an upright neck was crucial for these sauropods to survive. [3]

Related Research Articles

<i>Apatosaurus</i> Sauropod dinosaur genus from Late Jurassic period

Apatosaurus is a genus of herbivorous sauropod dinosaur that lived in North America during the Late Jurassic period. Othniel Charles Marsh described and named the first-known species, A. ajax, in 1877, and a second species, A. louisae, was discovered and named by William H. Holland in 1916. Apatosaurus lived about 152 to 151 million years ago (mya), during the late Kimmeridgian to early Tithonian age, and are now known from fossils in the Morrison Formation of modern-day Colorado, Oklahoma, New Mexico, Wyoming, and Utah in the United States. Apatosaurus had an average length of 21–23 m (69–75 ft), and an average mass of 16.4–22.4 t. A few specimens indicate a maximum length of 11–30% greater than average and a mass of approximately 33 t.

<i>Supersaurus</i> Extinct genus of dinosaurs

Supersaurus is a genus of diplodocid sauropod dinosaur that lived in North America during the Late Jurassic period. The type species, S. vivianae, was first discovered by Vivian Jones of Delta, Colorado, in the middle Morrison Formation of Colorado in 1972. The fossil remains came from the Brushy Basin Member of the formation, dating between 153 to 145 million years ago. It was a very large sauropod, with the WDC and BYU specimens reaching 33–35 metres (108–115 ft) in length and approximately 35–40 metric tons in body mass. A potential second species, S. lourinhanensis, (Dinheirosaurus) is known from Portugal and has been dated to a similar time.

<span class="mw-page-title-main">Sauropoda</span> Extinct clade of saurischian dinosaurs

Sauropoda, whose members are known as sauropods, is a clade of saurischian ('lizard-hipped') dinosaurs. Sauropods had very long necks, long tails, small heads, and four thick, pillar-like legs. They are notable for the enormous sizes attained by some species, and the group includes the largest animals to have ever lived on land. Well-known genera include Brachiosaurus, Diplodocus, Apatosaurus, Camarasaurus and Brontosaurus.

<i>Camarasaurus</i> Camarasaurid sauropod dinosaur genus from Late Jurassic Period

Camarasaurus was a genus of quadrupedal, herbivorous dinosaurs and is the most common North American sauropod fossil. Its fossil remains have been found in the Morrison Formation, dating to the Late Jurassic epoch, between 155 and 145 million years ago.

<span class="mw-page-title-main">Diplodocidae</span> Extinct family of dinosaurs

Diplodocids, or members of the family Diplodocidae, are a group of sauropod dinosaurs. The family includes some of the longest creatures ever to walk the Earth, including Diplodocus and Supersaurus, some of which may have reached lengths of up to 42 metres (138 ft).

<i>Barosaurus</i> Diplodocid sauropod dinosaur genus from Upper Jurassic Period

Barosaurus was a giant, long-tailed, long-necked, plant-eating sauropod dinosaur closely related to the more familiar Diplodocus. Remains have been found in the Morrison Formation from the Upper Jurassic Period of Utah and South Dakota. It is present in stratigraphic zones 2–5.

<span class="mw-page-title-main">Macronaria</span> Extinct clade of dinosaurs

Macronaria is a clade of sauropod dinosaurs. Macronarians are named after the large diameter of the nasal opening of their skull, known as the external naris, which exceeded the size of the orbit, the skull opening where the eye is located. Fossil evidence suggests that macronarian dinosaurs lived from the Middle Jurassic (Bathonian) through the Late Cretaceous (Maastrichtian). Macronarians have been found globally, including discoveries in Argentina, the United States, Portugal, China, and Tanzania. Like other sauropods, they are known to have inhabited primarily terrestrial areas, and little evidence exists to suggest that they spent much time in coastal environments. Macronarians are diagnosed through their distinct characters on their skulls, as well as appendicular and vertebral characters. Macronaria is composed of several subclades and families notably including Camarasauridae and Titanosauriformes, among several others. Titanosauriforms are particularly well known for being some of the largest terrestrial animals to ever exist.

<i>Opisthocoelicaudia</i> Sauropod dinosaur genus from Late Cretaceous Mongolia

Opisthocoelicaudia is a genus of sauropod dinosaur of the Late Cretaceous Period discovered in the Gobi Desert of Mongolia. The type species is Opisthocoelicaudia skarzynskii. A well-preserved skeleton lacking only the head and neck was unearthed in 1965 by Polish and Mongolian scientists, making Opisthocoelicaudia one of the best known sauropods from the Late Cretaceous. Tooth marks on this skeleton indicate that large carnivorous dinosaurs had fed on the carcass and possibly had carried away the now-missing parts. To date, only two additional, much less complete specimens are known, including part of a shoulder and a fragmentary tail. A relatively small sauropod, Opisthocoelicaudia measured about 11.4–13 m (37–43 ft) in length. Like other sauropods, it would have been characterised by a small head sitting on a very long neck and a barrel shaped trunk carried by four column-like legs. The name Opisthocoelicaudia means "posterior cavity tail", alluding to the unusual, opisthocoel condition of the anterior tail vertebrae that were concave on their posterior sides. This and other skeletal features lead researchers to propose that Opisthocoelicaudia was able to rear on its hindlegs.

<i>Euhelopus</i> Extinct genus of dinosaurs

Euhelopus is a genus of sauropod dinosaur that lived between 145 and 133 million years ago during the Berriasian and Valanginian stages of the Early Cretaceous in what is now Shandong Province in China. It was a large quadrupedal herbivore. Like sauropods such as brachiosaurs and titanosaurs, Euhelopus had longer forelegs than hind legs. This discovery was paleontologically significant because it represented the first dinosaur scientifically investigated from China: seen in 1913, rediscovered in 1922, and excavated in 1923 and studied by T'an during the same year. Unlike most sauropod specimens, it has a relatively complete skull.

<i>Brontosaurus</i> Genus of diplodocid sauropod dinosaur

Brontosaurus is a genus of herbivorous sauropod dinosaur that lived in present-day United States during the Late Jurassic period. It was described by American paleontologist Othniel Charles Marsh in 1879, the type species being dubbed B. excelsus, based on a partial skeleton lacking a skull found in Como Bluff, Wyoming. In subsequent years, two more species of Brontosaurus were named: B. parvus in 1902 and B. yahnahpin in 1994. Brontosaurus lived about 156 to 146 million years ago (mya) during the Kimmeridgian and Tithonian ages in the Morrison Formation of what is now Utah and Wyoming. For decades, the animal was thought to have been a taxonomic synonym of its close relative Apatosaurus, but a 2015 study by Emmanuel Tschopp and colleagues found it to be distinct. It has seen widespread representation in popular culture, being the archetypal "long-necked" dinosaur in general media.

<i>Patagosaurus</i> Extinct genus of dinosaurs

Patagosaurus is an extinct genus of eusauropod dinosaur from the Middle-Late Toarcian of Patagonia, Argentina. It was first found in deposits of the Cañadón Asfalto Formation, which date to around 179 to 177 million years ago. Although originally twelve specimens were assigned to the taxon, at least one of them may belong to a different genus. Patagosaurus probably lived alongside genera as Piatnitzkysaurus, Condorraptor and Volkheimeria.

<i>Europasaurus</i> Extinct genus of dinosaurs

Europasaurus is a basal macronarian sauropod, a form of quadrupedal herbivorous dinosaur. It lived during the Late Jurassic of northern Germany, and has been identified as an example of insular dwarfism resulting from the isolation of a sauropod population on an island within the Lower Saxony basin.

<span class="mw-page-title-main">Camarasauridae</span> Extinct family of dinosaurs

Camarasauridae is a family of sauropod dinosaurs. Among sauropods, camarasaurids are small to medium-sized, with relatively short necks. They are visually identifiable by a short skull with large nares, and broad, spatulate teeth filling a thick jaw. Based on cervical vertebrae and cervical rib biomechanics, camarasaurids most likely moved their necks in a vertical, rather than horizontal, sweeping motion, in contrast to most diplodocids.

<span class="mw-page-title-main">Neosauropoda</span> Extinct clade of dinosaurs

Neosauropoda is a clade within Dinosauria, coined in 1986 by Argentine paleontologist José Bonaparte and currently described as Saltasaurus loricatus, Diplodocus longus, and all animals directly descended from their most recent common ancestor. The group is composed of two subgroups: Diplodocoidea and Macronaria. Arising in the early Jurassic and persisting until the Cretaceous-Paleogene extinction event, Neosauropoda contains the majority of sauropod genera, including genera such as Apatosaurus, Brachiosaurus, and Diplodocus. It also includes giants such as Argentinosaurus, Patagotitan and Sauroposeidon, and its members remain the largest land animals ever to have lived.

<span class="mw-page-title-main">Apatosaurinae</span> Extinct subfamily of dinosaurs

Apatosaurinae is a subfamily of diplodocid sauropods, an extinct group of large, quadrupedal dinosaurs, the other subfamily in Diplodocidae being Diplodocinae. Apatosaurines are distinguished by their more robust, stocky builds and shorter necks proportionally to the rest of their bodies. Several fairly complete specimens are known, giving a comprehensive view of apatosaurine anatomy.

<i>Amphicoelias</i> Extinct genus of dinosaurs

Amphicoelias is a genus of herbivorous sauropod dinosaur that lived approximately 150 million years ago during the Tithonian of what is now Colorado, United States. Amphicoelias was moderately sized at about 18 metres (59 ft) in length and 15 metric tons in body mass, shorter than its close relative Diplodocus. Its hindlimbs were very long and thin, and its forelimbs were proportionally longer than in relatives.

<i>Diplodocus</i> Genus of diplodocid sauropod dinosaurs (fossil)

Diplodocus was a genus of diplodocid sauropod dinosaurs, whose fossils were first discovered in 1877 by S. W. Williston. The generic name, coined by Othniel Charles Marsh in 1878, is a Neo-Latin term derived from Greek διπλός (diplos) "double" and δοκός (dokos) "beam", in reference to the double-beamed chevron bones located in the underside of the tail, which were then considered unique.

<i>Brachiosaurus</i> Sauropod dinosaur genus from the late Jurassic Period

Brachiosaurus is a genus of sauropod dinosaur that lived in North America during the Late Jurassic, about 154 to 150 million years ago. It was first described by American paleontologist Elmer S. Riggs in 1903 from fossils found in the Colorado River valley in western Colorado, United States. Riggs named the dinosaur Brachiosaurus altithorax; the generic name is Greek for "arm lizard", in reference to its proportionately long arms, and the specific name means "deep chest". Brachiosaurus is estimated to have been between 18 and 22 meters long; body mass estimates of the subadult holotype specimen range from 28.3 to 46.9 metric tons. It had a disproportionately long neck, small skull, and large overall size, all of which are typical for sauropods. Atypically, Brachiosaurus had longer forelimbs than hindlimbs, which resulted in a steeply inclined trunk, and a proportionally shorter tail.

<i>Nigersaurus</i> Genus of reptiles (fossil)

Nigersaurus is a genus of rebbachisaurid sauropod dinosaur that lived during the middle Cretaceous period, about 115 to 105 million years ago. It was discovered in the Elrhaz Formation in an area called Gadoufaoua, in Niger. Fossils of this dinosaur were first described in 1976, but it was only named Nigersaurus taqueti in 1999, after further and more complete remains were found and described. The genus name means "Niger reptile", and the specific name honours the palaeontologist Philippe Taquet, who discovered the first remains.

<i>Yongjinglong</i> Extinct genus of dinosaurs

Yongjinglong is an extinct genus of titanosauriform sauropod dinosaur known from the Early Cretaceous of Lanzhou-Minhe Basin of Gansu Province, China. It contains a single species, Yongjinglong datangi.

References

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  2. 1 2 Seymour, R. S.; Lillywhite, H. B. (2000). "Hearts, neck posture and metabolic intensity of sauropod dinosaurs". Proceedings of the Royal Society B: Biological Sciences. 267 (1455): 1883–7. doi:10.1098/rspb.2000.1225. PMC   1690760 . PMID   11052540.
  3. 1 2 Christian, A. (2010). "Some sauropods raised their necks–evidence for high browsing in Euhelopus zdanskyi". Biology Letters. 6 (6): 823–825. doi:10.1098/rsbl.2010.0359. PMC   3001369 . PMID   20519198.
  4. ↑ Cobley, M. J.; Rayfield, E. J.; Barrett, P. M. (2013). "Inter-Vertebral Flexibility of the Ostrich Neck: Implications for Estimating Sauropod Neck Flexibility". PLOS ONE. 8 (8): e72187. doi: 10.1371/journal.pone.0072187 . PMC   3743800 . PMID   23967284.
  5. ↑ Taylor, M.P. (2014). "Quantifying the effect of intervertebral cartilage on the neutral posture in the necks of sauropod dinosaurs". PeerJ. 2: e712. doi: 10.7717/peerj.712 . PMC   4277489 . PMID   25551027.
  6. ↑ Christian, Andreas (2008). "Neck posture and overall body design in sauropods". Fossil Record. 5 (1): 271–281. doi: 10.1002/mmng.20020050116 .
  7. ↑ Franz, R.; Hummel, J.; Keinzle, E.; Kölle, P.; Gunga, H-C.; Clauss, M. (2009). "Allometry of visceral organs in living amniotes and its implications for sauropod dinosaurs". Proceedings of the Royal Society B: Biological Sciences. 276 (1662): 1731–1736. doi:10.1098/rspb.2008.1735. PMC   2660986 . PMID   19324837.
  8. ↑ Seymour, R. S. (2009). "Raising the sauropod neck: It costs more to get less". Biology Letters. 5 (3): 317–9. doi:10.1098/rsbl.2009.0096. PMC   2679936 . PMID   19364714.
  9. ↑ Choy, DS; Altman, P (1992-08-29). "The cardiovascular system of barosaurus: an educated guess". Lancet. 340 (8818): 534–6. doi: 10.1016/0140-6736(92)91722-k . PMID   1354287. S2CID   7378155.
  10. ↑ Borsuk-Białynicka, M.M. (1977). "A new camarasaurid sauropod Opisthocoelicaudia skarzynskii gen. n., sp. n. from the Upper Cretaceous of Mongolia" (PDF). Palaeontologia Polonica. 37: 5–64.
  11. 1 2 3 Schwarz, Daniela; Frey, Eberhard; Meyer, Christian A. (2007). "Novel reconstruction of the orientation of the pectoral girdle in sauropods". The Anatomical Record. 290 (1): 32–47. doi:10.1002/ar.20405. PMID   17441196.
  12. 1 2 Stevens, K. A. (1999). "Neck Posture and Feeding Habits of Two Jurassic Sauropod Dinosaurs". Science. 284 (5415): 798–800. doi:10.1126/science.284.5415.798. PMID   10221910.
  13. 1 2 Stevens, K.A.; Parrish, J.M. (2005). "Neck Posture, Dentition, and Feeding Strategies in Jurassic Sauropod Dinosaurs". In Tidwell, Virginia; Carpenter, Kenneth (eds.). Thunder-lizards: The Sauropodomorph Dinosaurs. Bloomington: Indiana University Press. pp. 212–232. ISBN   978-0-253-34542-4.
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