Everything about Sauropod totally explained
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's 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 didn't 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's a possibility they'd 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.
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're considered
paraphyletic, or even (in the case of Camarasauridae)
polyphyletic.
Classification
This taxonomy follows Wilson & Sereno 1998, Yates 2003, Galton 2001,
(External Link
) and Wilson 2002,
Phylogeny
Cladogram simplified after Wilson, 2002.
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