AskDefine | Define sauropod

Dictionary Definition

sauropod n : very large herbivorous dinosaur of the Jurassic and Cretaceous having a small head a long neck and tail and five-toed limbs; largest known land animal [syn: sauropod dinosaur]

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English

Noun

  1. A member of the Sauropoda suborder of dinosaurs

Extensive Definition

Sauropoda (), or the sauropods (/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.
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. Some palaeontologists have postulated that these bits are those most likely to be carried off by Mesozoic scavengers after the death of the animal and before it is covered by sediment and fossilised.

Size

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. 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, 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. Their legs were thick, ending in blunt feet with five toes.

Armor

Some sauropods had armour. 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 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 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.

Phylogeny

Cladogram simplified after Wilson, 2002.

References

Further reading

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sauropod in Catalan: Sauròpode
sauropod in Czech: Sauropodi
sauropod in Danish: Sauropod
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sauropod in Hebrew: זאורופודה
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sauropod in Japanese: 竜脚下目
sauropod in Norwegian: Sauropoder
sauropod in Norwegian Nynorsk: Sauropod
sauropod in Polish: Zauropody
sauropod in Portuguese: Saurópodes
sauropod in Russian: Зауроподы
sauropod in Simple English: Sauropods
sauropod in Slovak: Sauropoda
sauropod in Finnish: Sauropodit
sauropod in Swedish: Sauropoder
sauropod in Chinese: 蜥腳下目
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