Contrary to popular belief, it is not possible to swallow your tongue. If you’re human at least. It turns out that toads do this on purpose every time they eat.
“We know a lot about how frogs extend their tongues and how they latch onto their prey, but before this study, virtually everything that happens after they close their mouths was a mystery,” says herpetologist Rachel Keeffe of the University of Florida. .
So Keeffe and his colleagues used high-speed X-ray video to understand what happens when these amphibians close their mouths on a meal, and the results were completely unexpected.
“We weren’t sure what was going on at first,” says Keeffe. “The whole floor of the mouth was pulled back into the throat and the tongue with it.”
It took months of careful study of cane toads (Marina Rhinella) as they ate hundreds of crickets (Gryllodes sigillatus) and creating 3D animations to mess around with this strange power mechanism.
Frogs are well-known for capturing their prey with quick, sticky tongues, but therein lies the problem their unusual anatomy had to solve: how to remove post-feeding from this sticky whip to drop it into their guts .
From capture to ingestion, the whole process takes less than two seconds, but there’s a whole series of events that happen inside the frog in that short amount of time.
The team attached tiny metal beads to the toad’s tongue so they could track the muscle’s movements in the X-ray footage. As seen in the video below, the orange marker on the tip of its tongue darts out to grab an insect, then catches back. in the toad’s mouth. But it doesn’t stop there, continuing down the neck for a full 4.5 centimeters (1.8 inches), until it almost touches the toad’s heart.
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“The average distance the tongue stretches during retraction equals or exceeds the average distance stretched during protrusion,” the researchers I am writing in their paper, explaining that maximum tongue protrusion was 4.1 cm on average.
Here near their heart, the hyoid—a flexible plate of cartilage suspended by strings of muscle—clips the tongue.
“The hyoid ejects and presses the tongue against the roof of the mouth, after which it moves forward, essentially scraping the food into the esophagus,” explains Keeffe.
The hyoid (which some toads also use to make click calls) naturally seals the floor of the mouth while the toad rests. But its connection to the tongue means it opens as the muscle stretches, opening wide as the toad opens its mouth, ready for the tongue’s sharp thrust back.
That’s probably why toads and many frogs have strange ridges or “teeth” like bumps on the roof of their mouths, Keeffe and team suspect. to help loosen this food. Hyoid markers hit this area precisely in the researchers’ 3D reconstruction. The flexibility of the hyoid would also aid in the task of scraping.
“Even if a toad repositions the tongue inside the mouth during a double swallow, the prey remains attached to the tongue throughout the manipulation,” Keeffe and colleagues write. This suggests that frogs need the hyoid apparatus to remove their food successfully.
The researchers now want to repeat these investigations to see if this recoil and tongue-scraping feeding mechanism is universal across the nearly 5,000 species of frogs, among which there is a huge variety of hyoid and tongue shapes.
This research was published in Organismal Biology.