2 June 2009

Dinosaur posture still wrong, says study

By
Cosmos Online
The current depiction of the way giant sauropod dinosaurs held their necks is probably wrong, according to a study of the posture of modern animals.
Sauropods

Artist’s impression of a sauropod herd with the correct (neck aloft) posture. Credit: Mark Witton

BRISBANE: The current depiction of the way giant sauropod dinosaurs held their necks is probably wrong, says a new study.

“For the last decade the reigning paradigm in palaeontology has been that the big sauropod dinosaurs held their necks out straight and their heads down low,” said co-author Matt Wedel, who researches biomechanics at the Western University of Health Sciences in Pomona, California.

But “our research [now] suggests that this view of sauropods is simply incorrect, based on everything we know about living animals,” he said.

Unrealistic posture

According to the report in the journal Acta Palaeontologica Polonica, sauropods held their necks up in the same way as many living vertebrates, in a swan-like ‘s’ curve, rather than in the horizontal pose commonly shown in everything from museum reconstructions to plastic toys.

For many decades, scientists supposed that sauropods had long necks so they could browse high in the treetops and depicted them, like giraffes, with their heads held high. But a 1999 Science paper led to a shift in the way sauropods were shown.

The authors of that paper argued that the habitual pose of an animal’s neck could be easily found by lining up the vertebrae in maximum contact, which gave a horizontal pose for most sauropods. Estimates of blood pressure also suggested that it would have been very difficult for sauropods to pump their blood up to such a height.

Blood pressure problem

“The problem is, living animals don’t hold their necks in that posture,” Wedel said. After stumbling across a paper from the 1980s that showed that most land animals held their necks vertically, Wedel’s team looked for clues to sauropod posture in X-rays of living animals.

They found that reptiles and amphibians held their necks mostly horizontally, while mammals and birds (which are more closely related to dinosaurs and share their upright leg structures) all held their necks vertically.

Studying the neck movements of living creatures also suggested that sauropods had a greater range of movement than previously thought.

While scientists had assumed that the dinosaur neck vertebrae overlapped each other by around 50%, that’s not true for living creatures like ostriches and giraffes, which can extend their necks till the vertebrae hardly overlap at all.

Their method was so simple that the team was worried someone else would publish the findings before they could. “We did get a bit paranoid… it just seemed so obvious that if you want to know what extinct animals did, you should look at what living animals actually do,” Wedel told Cosmos Online.

John Hutchinson, a biomechanics researcher at the University of London’s Royal Veterinary College, in Britain, said that the study’s methods had the advantage of being firmly grounded in actual observations of animal anatomy and behaviour, but there is still work to be done to confirm the findings.

“A conundrum that remains unresolved is how sauropods would have pumped blood to their heads if held so high,” he said. “The blood pressures, and hence heart sizes, required are quite large.”

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