Contrary to popular belief, it is impossible to swallow your tongue. If you are human, at least. Frogs tend to act on purpose every time they eat.
“We know a lot about how frogs extend their tongues and how they attach to their prey, but before this study, everything that happens when they close their mouths was a mystery,” says Rachel Keeffe, a biologist at the University of Florida.
So Keeffe and his colleagues used high-speed X-ray video to find out what was happening when these marine animals closed their mouths to eat, and the results were completely unexpected.
“We didn’t know what was going on at first,” says Keeffe. “The whole floor of the mouth was pulled back into the throat and the tongue along with it.”
It took months of careful study of cane toads (Rhinella Marine) while they ate hundreds of crickets (Sealed Gryllodes) and create 3D animations to understand this amazing feeding system.
Frogs are well known for catching prey with their quick, sticky tongues, but therein lies a challenge their unusual bodies must overcome: how to extract food from the sticky whip to send it to their guts.
From being caught to being swallowed, it all takes less than two seconds, but there is a lot going on inside the frog in that short time.
The team attaches tiny beads to the frogs’ tongues to monitor muscle movements on x-ray images. As the video below shows, the orange markings on the tip of the frog’s tongue are used to catch insects, then back into the frog’s mouth. But it doesn’t stop there, it continues down the throat 4.5 centimeters (1.8 inches), until it almost touches the frog’s heart.
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“The distance the tongue extends during retraction equals or exceeds the maximum distance it extends during protraction,” the researchers said. write it down in their paper, describing the maximum protrusion of the tongue was 4.1 centimeters on average.
Here near their heart, the hyoid – a flexible plate of cartilage suspended by strings of muscle – closes with the tongue.
“The hyoid protrudes and pushes the tongue against the roof of the mouth, then it moves forward, throwing food down the esophagus,” explains Keeffe.
The hyoid (which some frogs also use to make calls) naturally seals the bottom of the mouth when the frog breathes. But its connection to the tongue means that it opens as the muscles grow, opening as the frog opens its mouth, ready for the tongue to move.
This is probably why many frogs and toads have unusual ridges or ‘teeth’ on their mouths, Keeffe is a skeptical group; help in removing this food. The hyoid markers accurately hit the spot in the researchers’ 3D reconstruction. The flexion of the hyoid can also help in its abduction function.
“Even when the frog reinserts its tongue into its mouth twice, the animal remains tongue-tied throughout the experiment,” write Keeffe and colleagues. This suggests that frogs need the hyoid system to efficiently digest their food.
The researchers are eager to repeat this study to see if this tongue is regressing and if the feeding method is found around the world in about 5,000 species of frogs, among them there are many species of color and tongue.
This study was published in Natural Biology.