Cane Toad Swallowing Tongue

Something Really Weird Happens When A Cane Toad Sits Down To Eat

Contrary to popular belief, it is not possible for you to swallow your own tongue. If you’re human, at least. Turns out toads do this on purpose every time they eat.

“We know a lot about how frogs extend their tongues and how they stick to their prey, but before this study, everything that happened after they closed their mouths was a mystery,” says Rachel. Keeffe, herpetologist at the University of Florida.

So Keeffe and his colleagues used high-speed X-ray video to figure out what was happening when these amphibians closed their mouths around 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 to carefully study the cane toads (navy rhineland) as they ate hundreds of crickets (Sealed Grylodes) and create 3D animations to unravel this bizarre feeding mechanism.

Frogs are well known for capturing prey with quick, sticky tongues, but therein lies the problem their unusual anatomy had to solve: how to then get food out of that sticky whip and into their guts.

From capture to swallow, the whole process takes less than two seconds, but there are a whole series of events that occur in the toad during this short period of time.

The team attached tiny metal beads to the toad’s tongue so they could track the movements of the muscle in the x-ray images. As shown in the video below, the orange marker on the tip of its tongue goes wild to catch an insect, then returns to the toad’s mouth. But it doesn’t stop there, continuing down the throat for 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 is equal to or greater than the average distance it stretches during protrusion. write in their article, explaining that 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 chains of muscle – closes against the tongue.

“The hyoid bone lifts up and presses the tongue against the roof of the mouth, after which it moves forward, essentially scraping food into the esophagus,” Keeffe explains.

The hyoid (which some toads also use to click) naturally seals the floor of the mouth while the toad is resting. But its connection to the tongue means it opens when the muscle extends, opening wide when the toad opens its mouth, ready for the return of the tongue.

Diagram showing the anatomy of the toad's mouth
Anatomy of the toad’s mouth showing the position of the skeleton (grey), hyoid bone (blue), and muscles (pink). (Keeffe et al., Biology of organisms2022)

This is likely why toads and many frogs have strange ridges or bump-like “teeth” on the roof of their mouths, Keeffe and his team suspect; to help with this detachment of food. Hyoid markers hit this area precisely in the researchers’ 3D reconstruction. The flexibility of the hyoid would also help with its scratching task.

“Even if a toad repositions the tongue in 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 mechanism to successfully dislodge their food.

The researchers now want to repeat these investigations to see if this recoil-and-scrape feeding mechanism is universal among nearly 5,000 species of frogs, among which there is a wide diversity of hyoid and tongue shapes.

This research was published in Biology of organisms.

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