By Victoria Gill
Science reporter, BBC News
Keeping its head down: the Natural History Museum's diplodocus will not need to be "re-posed"
Diplodocus's impressive neck sweeps along the main hall of London's Natural History museum, welcoming its visitors.
Now, findings suggest that 150 million years ago the giant may have held its head higher for much of the time.
By studying the skeletons of living vertebrates, Mike Taylor, from the University of Portsmouth, and his team, reshaped the dinosaur's resting pose.
But there is more than one way to assemble a dino-skeleton, and more than one theory on the sauropods' stance.
Dr Taylor said he is not suggesting that museums should re-pose their long-necked sauropod skeletons from the current horizontal position to a more upright posture.
"The diplodocus in the main hall vestibule of the Natural History Museum is in a perfectly good posture," he told BBC News. "It's one within a whole range of movement that would have been entirely possible."
But, after studying X-rays of members of 10 different vertebrate groups, Dr Taylor is convinced that when they were not reaching down for a drink, the sauropods stood with their heads held very high indeed.
With their necks aloft, like giraffes, the dinosaurs would have towered up to 15m above the ground.
Dr Taylor and his colleagues found that the necks of mammals and birds - the only modern groups that share the upright leg posture of dinosaurs - are "strongly inclined" vertically.
"Our approach was embarrassingly straightforward," said Dr Taylor. "We looked at real animals, and at the whole animal."
Bones can only give us so much information, he explained, and the soft tissue in the animal's huge neck could "enable greater flexibility than the bones alone suggest".
Some of the earliest reconstructions of sauropod skeletons - in the late 19th and early 20th Century - were posed with erect necks, so the idea is not new.
"It's largely in recent years that this view has changed," Dr Taylor said.
"But we can be confident that they held their heads upright."
Many scientists, however, still maintain a more horizontal view.
And a recent paper, published by Australian scientist Roger Seymour in the journal Biology Letters, went even further.
It suggested that the creatures would not actually be able to lift their heads up to eat from high trees, because this would raise their brains so far above their hearts that their blood pressure would have to be elevated to a dangerous - possibly lethal - level.
But Dr Taylor is not swayed by this argument.
"There are some [living animals] where the heart is able to exert much greater pressure than Seymour's equations predict [is possible]. We don't see why that couldn't also be true in sauropods."
Paul Barrett, a palaeontologist from London's Natural History Museum, thinks the sauropods were likely to have been able to lift their heads high, but he remains unconvinced that would have been their "resting posture".
"It would require lots of muscular activity, and put a lot of strain on their hearts," he said.
The upright posture is especially evident in birds
Dr Barrett explained that, since it is impossible to know how thick the pads of connective tissue between the dinosaurs' vertebrae were, it is difficult to estimate how much of a role this tissue, along with muscles and tendons, played in the animals' range of movement.
"Sauropods are bizarre," he told BBC News. "There is no living animal built in the same way."
So, although the study of living animals' skeletons is very valuable, he added, "finding a model to explain the biology of these creatures is not that easy".