Exploding dinosaur theory EXPLODED

Bone botherers blast belly-burst boffinry

Bone-bothering boffins have long theorised that sea-dwelling ichthyosaurs were prone to exploding because their skeletons are often found in a scattered pattern.

Not that a time-traveller from the future was there and lobbed a hand grenade at them - but that the creatures' decomposition process produced enough putrefaction gases to cause the dead underwater monsters to swell up and burst.

The ichthyosaur, a marine tetrapod, was thought to float on the surface of the seawater after death until it blimped up enough to erupt and sink to the bottom, a theory that was supported by a mother ichthyosaur skeleton that was found intact with the scattered bones of her embryos around her.

Scientists hypothesised that the embryos exploded under the putrefaction gas pressure, leaving the mother's skeleton to sink to the bottom in one piece.

But boffins from universities in Zurich and Basel are now discounting the idea that the carcasses ruptured.

Human corpses are surprisingly similar to ichthyosaurs and about the same size, so the researchers measured the internal pressure of a hundred bodies in different stages of bloating.

They found that the pressure inside the abdominal cavity never exceeded 0.035 bar. Meanwhile in goats, the pressure only went up to 0.079 bar. This would have placed the corpses 0.35m and 0.79m below the surface, respectively.

Where the ichthyosaur bodies went down, the water depths were between 50m and 150m, so it would have taken 5 to 15 bar of internal pressure to make the corpses explode.

"Large vertebrates that decompose cannot act as natural explosive charges," said Zurich palaeontologist Christian Klug in a canned statement. "Our results can be extended to lung-breathing vertebrates in general."

Instead, these boffins think that the ichthyosaurs sank to the seabed immediately after death and were then broken down by putrefaction and scavengers. But if the water was at the shallow end of the scale, up to 50m, and at temperatures of over four degrees Celsius, the carcass could rise back up to the surface on the strength of the putrefaction gases.

Up there, with waves slapping the already-scavenged corpses and other carrion-eaters getting in on the action, the ichthyosaur was broken down further, leaving the bones to sink individually over a wide area.

While this solution is nowhere near as exciting as exploding Mesozoic-era creatures, it does have some applications in modern life, where knowledge of how postmortem pressures, temperatures and scavenging rates affect corpses can help in the retrieval of human bodies after disasters or horrific crimes.

The study is published [PDF] in the current issue of Palaeobiodiversity and Palaeoenvironments. ®