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Sharks shrug shoulders at feeding study

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By Agence France-Presse

How does a bamboo shark, which uses suction to latch on to its prey, swallow a wriggling, reluctant meal?

With a shrug of its shoulders, according to a study published Wednesday in the journal Proceedings of the Royal Society B.

This file photo taken on September 03, 2011 shows a baby bamboo shark swim over a coral reef following its release into the sea as part of an operation organised by the sharks protection group Dive Tribe off the coast of the southern Thai sea resort of Pattaya. How does a bamboo shark, which uses suction to latch on to its prey, swallow a wriggling, reluctant meal? With a shrug of it's shoulders, according to a study published on July 19, 2017 in the journal Proceedings of the Royal Society B. That rates as Big News for specialists, who have long assumed that U-shaped cartilage between the head and body existed only to control the predator's front-most fins. Not so, according to lead author Ariel Camp, a postdoctoral researcher at Brown University in the US state of Rhode Island. (AFP PHOTO / Christophe ARCHAMBAULT / MANILA BULLETIN)

This file photo taken on September 03, 2011 shows a baby bamboo shark swim over a coral reef following its release into the sea as part of an operation organised by the sharks protection group Dive Tribe off the coast of the southern Thai sea resort of Pattaya. (AFP PHOTO / Christophe ARCHAMBAULT / MANILA BULLETIN)

That rates as Big News for specialists, who have long assumed that U-shaped cartilage between the head and body existed only to control the predator’s front-most fins.

Not so, according to lead author Ariel Camp, a postdoctoral researcher at Brown University in the US state of Rhode Island.

“Sharks don’t have tongues to move food through their mouths,” she said in a statement. “They have this long pharynx, and they have to keep food moving down it.”

Bottom-feeding bamboo sharks, which grow to about a metre (three feet) and are harmless to humans, favour a diet of small fish and invertebrates such as crabs.

They create suction to grasp their prey, but Camp suspected that the cartilage played a role in pushing things along the digestive tract.

To find out, she and her team strategically implanted bits of tungsten carbide in three live sharks to see if the shoulder-like cartilage moved as the animals feasted in a laboratory setting.

They used a cutting-edge technology called X-ray Reconstruction of Moving Morphology, or X-ROMM, which combines CT scans of the skeleton with high-speed, high-resolution X-ray movies.

Sure enough, a fraction of a second after the mouth closed around a bit of squid or herring, the “shoulder girdle” quickly rotated backward — from head to tail — by about 11 degrees.

Camp suspects that other suction-feeding sharks also shrug their shoulders this way too.

 

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