Did dinosaurs hold their necks low to the ground when foraging for food to save energy, or did they hold their heads high? The debate continues.
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SYDNEY: Sauropod dinosaurs may have used their necks like vacuum cleaner hoses when feeding, new research has suggested, contributing to the raging debate amongst palaeontologists over whether these massive animals held their necks high like giraffes, or low, when feeding.
The problem that has plagued sauropod experts is the high cost of energy needed to pump blood around a long, raised neck. Using a new equation, researchers in the UK have shown that a 25-tonne Brachiosaurus could have used 80% less energy with a nine-metre-long neck than with a six-metre neck, as it could reach a wider area of low-growing vegetation whilst standing still.
“I think we came up with the vacuum cleaner analogy because my co-author and I are old enough to remember old-fashioned cylinder vacuum cleaners,” said Graeme Ruxton from the University of Glasgow in Scotland, referring to the vacuums used in the 1960s and 1970s, which had particularly long hoses to reach much of the room without having to keep moving the weighty vacuum cylinders around.
The ‘vacuum cleaner principle’
Previous studies involving sauropod neck posture have ranged from comparisons to small extant mammals to blood pressure measurements, each in the hope of explaining the possible behaviour of an animal with a body unlike anything we’ve ever seen.
In 2009, physiologist Roger Seymour of the University of Adelaide in Australia threw his support behind the ‘vacuum cleaner principle’, with a paper in Biology Letters stating that, “it would have required the animal to expend approximately half of its energy intake just to circulate the blood, primarily because a vertical neck would have required a high systemic arterial blood pressure."
"It is therefore energetically more feasible to have used a more or less horizontal neck to enable wide browsing while keeping blood pressure low,” Seymour concluded.
Comparing anatomy with living creatures
On the other hand, a team of scientists including anatomist Mathew Wedel from the Western University of Health Sciences in California published in Acta Palaeontologica Polonica that same year pointing to the fact that rabbits have a neck so vertical, it bends back on itself, and that the crocodile’s neck is also habitually elevated above neutral (with the neck in line with the torso) pose.
“Unless they were different from all extant terrestrial amniotes (a mammal, bird or reptile), they did not habitually hold their necks in neutral position, but raised well above horizontal." the team wrote.
"And if they resembled their closest relatives, the birds — and the only other homeothermic and erect-legged group, the mammals — then their necks were strongly inclined.”
