Hey, when you don't have a tongue, you've got to make do.
We have to admit, we haven't spent a lot of time thinking about how sharks eat. And it ever does cross our minds, it's usually during a viewing of the classic Jaws, staring in horror as the sawtoothed water beast devours its victims seemingly whole. But as a new study shows, the way sharks eat is actually quite interesting, in part because sharks don't have tongues. In fact, sharks have to swallow by swinging their shoulders.
Brown University researchers studied bamboo sharks—sharks way too small to eat humans—with X-ray movie technology to see how food got from the sharks' mouths and into their stomachs. (Cool note: it was the first time such tech has been used.)
Using tiny metal markers implanted into the sharks, the researchers were able to see—in high-resolution—how their bones and muscles moved when they ate both squid and herring. Human use their tongues (thing the back part of the muscle more than the tip) and our throat muscles to moved food down the esophagus. Sharks, instead, swallow by pulling their shoulders back, like we might to shrug or straighten our posture. That motion creates a suction effect, moving food from their mouths into their digestive tracks, the researchers found. (These sharks also use their shoulders to control their fins.)
The researchers say this motion makes a lot of sense, and not just because bamboo sharks don't lack tongues. These sharks feed on prey that often hides in crevices or in the silt of the sea floor, making it tough to do anything but suck them up for lunch.
But they were surprised to see the part their shoulders (technically, their "shoulder girdles") played in creating this suction. After all, sharks' shoulders aren't connected to their heads or jaws, so it's interesting these otherwise unrelated muscles are still used in feeding.
While this study focused exclusively on bamboo sharks, the researchers say other sharks and even some fish likely use their shoulder girdles to eat, too. *shrug* Who knew?