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Deep Diving Damaged Ichthyosaurian Bones

By Stephen Luntz

Ichthyosaurians, the giant predators that dominated the oceans during the age of the dinosaurs, suffered for their long dives in search of food, according to pathologist A/Prof John Hayman of the University of Melbourne.

In Naturwissenschaften: Science of Nature Hayman responded to research revealing bone deformities similar to divers who get the bends. Hayman is a diver, and says: “I’ve done quite a few autopsies on human divers but I am not a palaeontologist”. The deformities were attributed to the ichthyosaur surfacing too quickly, but Hayman says this is not the source of the problem in humans.

“If you surface too quickly without expelling air on the way up, your lungs will explode, but the bone scarring is a result of excess nitrogen dissolved in the body. This is a result of the amount of time spent at depth, not how quickly you come to the surface,” Hayman says.

“The nitrogen comes out of solution and forms bubbles that obstruct blood both in and out of the veins. This can occur either from the presence of the gas itself or damage to endothelial cells of the blood vessel, which causes clotting.”

Having observed the lesions on the ichthyosaurian bones, Hayman notes: “They are the same both as those in human divers and in sperm whales, suggesting the blood supply to bones such as the humerus has been conserved over 250 million years of evolution.

“The lesions wouldn’t have been enough to kill the animal, and wouldn’t have affected its ability to hunt or breed,” Hayman says. However, they might have resulted in arthritis later in life.