Sauropoda

Taxobox
name = Sauropods
fossil_range = Late Triassic - Late Cretaceous

---

image_width = 250px
image_caption = "Alamosaurus", a titanosaur.
regnum = Animalia
phylum = Chordata
classis = Sauropsida
superordo = Dinosauria
ordo = Saurischia
subordo = Sauropodomorpha
infraordo = Sauropoda
infraordo_authority = Marsh, 1878
subdivision_ranks = Families
subdivision = See text

"Sauropoda" (pronEng|sɔˈrɒpədə), or the sauropods (IPA|/ˈsɔroʊpɒd/), are a suborder or infraorder of the saurischian ("lizard-hipped") dinosaurs. They were the largest animals ever to have lived on land. Well-known genera include "Apatosaurus" (formerly known as "Brontosaurus"), "Brachiosaurus" and "Diplodocus". 'Sauropod' is derived from 'lizard foot' in Greek. Sauropods first appeared in the late Triassic Period, where they somewhat resembled the Prosauropoda. By the Late Jurassic (150 million years ago) sauropods were widespread (especially the diplodocids and brachiosaurids). By the Late Cretaceous, only the titanosaurians survived, though with a near-global distribution. However, as with all other non-avian dinosaurs, the titanosaurians died out in the Cretaceous-Tertiary extinction event. Fossilized remains have been found on every continent except Antarctica. The name Sauropoda was coined by O.C. Marsh in 1878.Marsh, O.C. (1878). "Principal characters of American Jurassic dinosaurs. Part I". "American Journal of Science and Arts" 16: 411-416]

Unfortunately, complete fossil sauropod finds are rare. Many species, especially the largest, are known only from isolated and disarticulated bones. Many near-complete specimens lack heads, tail tips and limbs.

ize

Sauropods' most defining characteristic was their size. Even the dwarf sauropods (perhaps 5 to 6 metres, or 20 feet long) were counted among the largest animals in their ecosystem. Their only real competitors in terms of size are the rorqual whales, such as the Blue Whale. But unlike whales, sauropods all lived on land. Some, like the diplodocids, probably held their heads low, while others, like Camarasaurus, held them high.

Their body design did not vary as much as other dinosaurs, perhaps due to size constraints, but they still displayed ample variety. Some, like the diplodocids, were extremely long and with tremendously long tails which they may have been able to crack like a whip to make sonic booms.cite web |url=http://www.sciencenews.org/articles/20000318/mathtrek.asp |title=Whips and Dinosaur Tails |accessdate=2007-07-07 |last=Peterson |first=Ivars |year=2000 |month=March |publisher= Science News ] "Supersaurus", at 40 metres (130 ft), is probably the longest, but "Seismosaurus" and even the old record holder, "Diplodocus", are still extremely long. "Amphicoelias fragillimus", of which only a drawing of a single vertebra survives, at 55 to 60 metres (180 to 200 ft) would have a spine even longer than the blue whale. The longest terrestrial animal alive today, the reticulated python, only reaches lengths of 10 metres (33 ft).

Others, like the brachiosaurids, were extremely tall, with high shoulders and extremely long necks. "Sauroposeidon" is probably the tallest, reaching about 18 metres (60 ft) high, with the previous record for longest neck being held by "Mamenchisaurus". By comparison the giraffe, the tallest of all living animals, is only 4.8 to 5.5 metres (16 to 18 ft) tall.

Some were almost incredibly massive: "Argentinosaurus" is probably the heaviest at 80 to 100 metric tonnes (90 to 110 tons), though "Paralititan", "Andesaurus", "Antarctosaurus", and "Argyrosaurus" are of comparable sizes. There is some very poor evidence of an even more massive titanosaurian, "Bruhathkayosaurus", which might have weighed between 175 to 220 tonnes (190 to 240 tons). The largest land animal alive today, the Savannah elephant, weighs no more than 10 tonnes (11 tons).

Among the smallest sauropods were the primitive "Anchisaurus" (2.4 m, or 7 ft long) and "Ohmdenosaurus" (4 m, or 13 ft long), the dwarf titanosaur "Magyarosaurus" (5.3 m or 17 ft long), and the dwarf brachiosaurid "Europasaurus" [Sander, P.M., Mateus, O., Laven, T. & Knötschke, N. 2006. Bone histology indicates insular dwarfism in a new Late Jurassic sauropod dinosaur. Nature, 441: 739-741.] , which was 6.2 meters long as a fully-grown adult. Its small stature was probably the result of insular dwarfism of a herd of sauropods stranded on an island in what is now Germany. Also notable is the diplodocoid sauropod "Brachytrachelopan", which was the shortest member of its group thanks to its unusually short neck. Unlike other sauropods, whose necks could grow to up to four times the length of their backs, the neck of "Brachytrachelopan" was shorter than its backbone.

Palaeobiology

They were herbivorous (plant-eating), usually long-necked quadrupeds (four-legged), with spatulate (spatula-shaped: broad at the base, narrow at the neck) teeth. They had small heads, huge bodies, and tended to have long tails. At least some of them laid eggs, like the camarasaurs and titanosaurs. According to paleontologist Robert Bakker there is a possibility they had large prehensile lips, reminiscent of moose lips.Fact|date=August 2007 Their legs were thick, ending in blunt feet with five toes.

Armor

Some sauropods had armor. There were genera with spined backs, such as the "Agustinia", and some has small clubs on their tails, like "Shunosaurus". Several titanosaurs, such as "Saltasaurus" and "Ampelosaurus", had small bony osteoderms covering portions of their bodies.

Posture

From early on there has been speculation by Osborn and others [Osborn HF."A skeleton of "Diplodocus", recently mounted in the American Museum,". Science, new series, vol. 10 (1899), pp. 870-874] that sauropods could reach up on hind legs, using their tail as the third 'leg' of a tripod (somewhat like kangaroos), and a famous restoration of a "Barosaurus" rearing up on hind legs in the American Museum of Natural History illustrates this hypothesis well. One interesting study [cite book|author=Rothschild BM, Molnar RE|year=2005|chapter=Sauropod Stress Fractures as Clues to Activity|editor=Carpenter, Kenneth and Tidswell, Virginia (ed.)|title=Thunder Lizards: The Sauropodomorph Dinosaurs|pages=381–391|publisher= Indiana University Press|id=ISBN 0-253-34542-1] has postulated that if sauropods had adopted a bipedal posture at times there would be evidence of stress fractures in the forelimb 'hands'. However, none were found after examining a large number of sauropod skeletons.

If a sauropod stood in the tripod posture, there would be a heavy weight load on the haemal spines on part of the tail. As the sauropod got heavier as it grew, when it reared, these haemal spines would have to carry more and more load, until some of them would break due to stress fracture, and that would make rearing painful and the sauropod would have to stay on four feet after that. That may have evolved as a safety measure to prevent rearing when it got too heavy for rearing to be safe. There are reports of such haemal spine fractures being found in sauropod tail vertebrae.

Taxonomy

Classification of the sauropods has largely stabilised in recent years, though there are still some uncertainties, such as the position of "Euhelopus", "Haplocanthosaurus", "Jobaria" and Nemegtosauridae. The following are two alternative recent classifications (showing supra-generic clades only in the second example). These are by no means an exhaustive list of recent sauropod classification schemes. In some cases, families like Vulcanodontidae, Cetiosauridae and Omeisauridae are not included because they are considered paraphyletic, or even (in the case of Camarasauridae) polyphyletic.

Classification

This taxonomy follows Wilson & Sereno 1998, Yates 2003, Galton 2001, [http://dml.cmnh.org/2003Jul/msg00103.html] and Wilson 2002, with ranks after Benton, 2004.Benton, M.J. (2004). "Vertebrate Palaeontology", Third Edition. Blackwell Publishing, 472 pp.]

*Infraorder Sauropoda
**"Ammosaurus"
**"Anchisaurus"
**?"Isanosaurus"
**"Kotasaurus"
**"Lessemsaurus"
**Family Blikanasauridae
**Family Melanorosauridae
**Family Vulcanodontidae
**Family Cetiosauridae
**Family Omeisauridae
**?Family Tendaguridae
**Clade Turiasauria
**Division Neosauropoda
***"Haplocanthosaurus"
***?"Jobaria"
***Superfamily Diplodocoidea
****Family Rebbachisauridae
****Family Dicraeosauridae
****Family Diplodocidae
***Subdivision Macronaria
****Family Brachiosauridae
****Family Camarasauridae
****Family Euhelopodidae
****Superfamily Titanosauroidea

Phylogeny

Cladogram simplified after Wilson, 2002.Wilson, J. A. (2002). "Sauropod dinosaur phylogeny: critique and cladistic analysis." "Zoological Journal of the Linnean Society", 136: 217-276.]

clade| style=font-size:100%;line-height:80%
label1=Sauropoda
1=clade
1="Vulcanodon"
label2=Eusauropoda
2=clade
1="Shunosaurus"
label2=unnamed
2=clade
1="Barapasaurus"
label2=unnamed
2=clade
1="Patagosaurus"
label2=unnamed
2=clade
1="Omeisaurus"
2="Mamenchisaurus"
label3=unnamed
3=clade
1="Jobaria"
label2=Neosauropoda
2=clade
1="Haplocanthosaurus"
2=Diplodocoidea
label3=Macronaria
3=clade
1="Camarasaurus"
label2=Titanosauriformes
2=clade
1="Brachiosaurus"
label2=Somphospondyli
2=clade
1="Euhelopus"
2=Titanosauria

References

Further reading

* Bob Strauss, 2008, [http://dinosaurs.about.com/od/typesofdinosaurs/a/sauropods.htm Sauropods: The Biggest Dinosaurs that Ever Lived] , The New York Times
* Kristina Curry Rogers and Jeffrey A. Wilson, 2005, "The Sauropods: Evolution and Paleobiology", University of California Press, Berkeley, ISBN 0-520-24623-3
* Upchurch, P., Barrett, P.M. and Dodson, P. 2004. Sauropoda. In "The Dinosauria", 2nd edition. D. Weishampel, P. Dodson, and H. Osmólska (eds.). University of California Press, Berkeley. Pp. 259-322.