Modern sea turtles rarely suffer from the bends, but fossil marine turtles were often afflicted.
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Photo by Brian Switek.
Modern sea turtles rarely suffer from the bends, but fossil marine turtles were often afflicted.

Turtle’s Got the Bends, Oh No

If you’re talking about Radiohead, “The Bends” is a good thing. Quite the contrary for diving. When a diver surfaces too fast, the pressure of the water changing around them as they go, Nitrogen in their body ekes out as bubbles that can cause everything from discomfort to death depending on where those bubbles go. But this isn’t a problem that started with the invention of the Aqua Lung. The bends have a fossil record that goes back over 220 million years.

Brain, spinal cord, blood vessels – we often think about the bends in relation to soft tissues. But the affliction also causes lesions on bones and around joints. That has left a mark on the skeletons of critters that were diving deep long before us.

In a paper published last year, paleopathologist Bruce Rothschild and colleagues picked out signs of decompression sickness on the skeletons of various ancient marine reptiles. Among the groups vulnerable to the bends were Jurassic and Cretaceous turtles. Now a Triassic turtle brings the bends back even further, giving the pathology a 220 million year history.

The unfortunate animal is Odontochelys semitestacea – an early turtle that still had teeth and was encased by a semi-shell of outer armor on the bottom with broad ribs on top. Possibly the descendant of a land-living ancestor, this unusual turtle’s bones have been found within the petrified wreck of a shallow marine habitat. And on the upper arm bones of the turtle, Rothschild and Virginia Naples report, there is bone damage that is the hallmark of the bends.

Both upper arm bones of the Odontochelys in the study are pocked around the portion that connected to the shoulder. This damage, Rothschild and Naples propose, is a sign that blood circulation around the bone was cut off by the effects of the bends, killing parts of the bone.

But why did this ancient turtle get the bends at all? We may never know what spurred this Odontochelys to rise too fast for the surface. Nevertheless, Rothschild and Naples hazard an explanation. A “gunboat in a sea of fear”, as Thom Yorke put it, may be to blame.

Some ancient predator may have chased frightened Odontochelys into the deep, leaving the turtle to rise too fast or drown. Then again, the situation could have unfolded the other way – with Odontochelys sprinting for the surface to escape – or perhaps the turtle simply made a mistake when young and inexperienced. Whatever happened, Rothschild and Naples suggest, the damaged bones might mean that early turtles lacked the physiological and behavioral tricks modern marine turtles have evolved to circumvent decompression sickness. Poor Odontochelys. All you wanted to do was live, breath… be part of the chelonian race.