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Ask Fuzzy: Fossils leave death clues

Question: What causes a death pose?

For years palaeontologists have pondered over the strange position many unearthed dinosaur skeletons are in. 

An "Opisthotonic" pose is just a scientific way of saying the head and tail are curved backwards over the spine. This "death pose" has been seen not only in dinosaurs, but birds, pterosaurs – even kangaroos and other long-necked mammals – though exactly why it happens is a total mystery. 

A number of theories have been proposed over the years, including the contraction of spine ligaments and tendons as the body dried out, rigor mortis or post-mortem moving by water or the ground itself.

One new theory suggests none of these are correct, that in fact the pose was created by muscle spasms created by a dying brain firing wild messages to the body. The resulting death throws from this would have included the contracting of muscles and ligaments, forcing the neck and tail to curl backwards over the spine, and the limbs to flex and retract into unnatural positions. This means the strange position occurred before death, not afterwards.

These deaths could have been caused by a number of things – infections, toxins, starvation, drowning or asphyxiation – but really it does not matter the cause as it was the brain, under the incredible stresses of dying, that caused the position, not the actual method of death.

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A recent test of chicken corpses may have answered the long sought-after question. When allowed to decompose in the sun, not a single chicken formed the death pose. However, when bodies were placed in water their necks almost immediately curled backwards in the pose. The same test left animal ligaments out in the sun to see if they ever shrank as they dried out. Though there was some shrinking, never was it considered enough to warp an entire skeleton into the position the fossils had been found in.

Strangely, another test of birds in water produced no such effect; and it's unclear why the results were so different. The fact the first was conducted in fresh water, while the second was in sal twater likely had something to do with the variations. 

This all indicates the fossils showing the death pose were formed when the corpse entered freshwater lakes or rivers, possibly when the animal either drowned or had died on land and been washed into the water by flooding.

Response by: Phil Hore, National Dinosaur Museum

Next week: More on death

Brought to you by the Fuzzy Logic science show, 11am Sundays on 2XX 98.3FM. Send your questions to askfuzzy@zoho.com. Twitter @FuzzyLogicSci