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Sauropoda, the sauropods, 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 the Brontosaurus), Brachiosaurus and Diplodocus.

Paleobiology

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 big flexible lips, reminiscent of moose lips.

Size

Sauropods' most defining characteristic was their size. Even the dwarf sauropods (perhaps 5 to 6 meters, or 20 feet long) were counted among the largest animals in their ecosystem. Their only real competitor in terms of size is the Balaenoptera musculus, or blue whale. But unlike the aquatic giant, they were all terrestrial. Some, like the diplodocids, probably held their heads low, while others, like the brachiosaurids, 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, with sails running down the back of their spines, and with tremendously long tails they may have been able to snap to create sonic booms. The Supersaurus, at 40 meters (130 feet), is probably the longest, but Seismosaurus and even the old record holder, the Diplodocus, are still extremely long. Though a possible century-old hoax, the Amphicoelias fragillimus, of which only a drawing of a single vertebra survives, at 55 to 60 meters (180 to 200 feet) would have a spine even longer than the B. musculus. The longest terrestrial animal alive today, the reticulated python, can only reach lengths of up to 10 meters (35 feet).

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

Some were almost incredibly massive, like the armor-plated titanosaurids. The Argentinosaurus is probably the heaviest at 80 to 100 metric tonnes (90 to 110 tons), though the Paralititan, Andesaurus, Antarctosaurus, and Argyrosaurus are of comparable sizes. And there is some very poor evidence of an even more massive titanosaurid, the Bruhathkayosaurus, which might weigh in at 125 to 170 tonnes (140 to 190 tons). The largest land animal alive today, the Savannah elephant, weighs no more than 10 tonnes (11 tons).

Body Armour

Some sauropods had armour. There were genera with spined backs, for instance the stegosaur-like (Agustinia) and one with a club-tail (the Shunosaurus), like the Ankylosaurus.

Posture

From the early days, 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, 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.

Tails

Old restorations had sauropods dragging their tails. However, more recently, they have been depicted as elevated off the ground. The evidence for this is provided by the stiffening structures between the tail vertebrae. Furthermore, fossilised sauropod tracks (ichnites) generally lack tail marks.

Incomplete Fossil Finds

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

Environment

Sauropods first appeared in the Late Triassic Period, where the early versions resembled the Prosauropoda. By the Late Jurassic (180 million years ago), the diplodocids and brachiosaurids were widespread, but they died out in the Early Cretaceous Period. The second great wave of sauropods, the titanosaurids, were distributed world-wide by the Late Cretaceous, until all dinosaurs perished, most likely as a result of a bolide impact leading to the Cretaceous-Tertiary extinction event. Fossilized remains have been found on every continent except Antarctica.

Classification

Classification of the sauropods is still very uncertain, especially with the euhelopods, though the cetiosaur, vulcanodont and nemegtosaur families also present many challenges. The titanosaur family has also been very poorly known, though the discovery of a complete skeleton of the Rapetosaurus is changing that.

The following are two alternative recent classifications (showing supra-generic clades only in the second example). These of course by no means exhaust the list of recent sauropod classification schemes. In some cases, families like Vulcanodontidae, Cetiosauridae, Omeisauridae, etc are not included because they are considered paraphyletic, or even (in the case of Camarosauridae) polyphyletic.

After Wilson & Sereno, 1998, Yates, 2003, Galton, 2001 *, and Wilson, 2002; ranks after Benton, 2004:

Suborder Sauropodomorpha

From Upchurch et al. 2004: (genera omitted, see above)

Recently-discovered short-necked variety

In June 2005, a new type of sauropod was discovered with a short, stubby neck. This new species, Brachytrachelopan mesai, measured less than 33 ft (10 m) long, which is unusually small for a sauropod. Unlike other sauropods, whose necks could grow to up to four times the length of their backs, Brachytrachelopan's neck was shorter than its backbone. Unable to lift its neck and head above horizontal, this shorter length was likely an adaptation to eating an abundant or nutritious low-growing plant. *

References

Sauropods

Sauropod | Sauropoden | Sauropoda | Sauropoda | Sauropoda | סאורופודה | Sauropoda | 竜脚下目 | sauropod | Zauropody | Sauropoda | Sauropoda | Sauropoder

 

This article is licensed under the GNU Free Documentation License. It uses material from the "Sauropoda".

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