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.
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 meter (three feet) and are harmless to humans, favor 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.