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Scientist probe ballistic chameleon tongue
The tongue of the chameleon shoots out at high speeds like a rubber band gun, working well even during freezing weather, US researchers have found.

Christopher Anderson and Dr Stephen Deban of the University of South Florida report their findings today in the Proceedings of the National Academy of Sciences.

The chameleon's near weatherproof tongue gives the reptile an edge over competitors.

They can exploit a wide range of environments as well as early morning peaks in prey activity even in the chilliest of alpine climates, according to the new study.

Anderson says a chameleon's tongue works similar to a spring in a ballpoint pen, a rubber band handgun or a bow and arrow.

In each case, he says, "a temperature-dependent muscle, or muscles, must initiate the mechanism," creating kinetic energy that then decouples from that first movement.

This allows the spring, rubber band, arrow or tongue to shoot out "on its momentum alone once launched".

"A chameleon's tongue travels at accelerations exceeding 400 metres per second squared, or about 41 Gs of force," adds Anderson.

To put that into perspective, a space shuttle only develops about three Gs of force when it takes off.
Feeding study

For the study, Anderson and Deban filmed five veiled chameleons (Chamaeleo calyptratus) feeding on crickets at a range of distances.

They placed the insects on what they call a "cricket trapeze," so that the chameleon's tongue could complete its trajectory naturally without being stopped by an immovable target.

In the wild, chameleons eat everything from birds and other lizards to all sorts of bugs.

The researchers next lowered temperature during the feeding events.

Prior studies determined that when other animals sprint, swim and jump, their muscle power decreases by at least 33% over each 10s04;C temperature drop.

Chameleon tongue speed, in contrast, fell by only about 10% over this same temperature reduction.

"Since chameleons worldwide feed in a similar manner, we believe our findings apply to all chameleons, from species living in desert habitats to those in alpine zones," says Anderson.
Rapid recoil

Anderson says that contraction of the chameleon's tongue accelerator muscle, which is wrapped in circular fashion around the rigid tongue bone, leads to "rapid elastic recoil of collagen tissue within the tongue".

About the only thing that might stop this nearly 20-centimetre-long recoil is extremely hot weather that can break down the tissue, essentially cooking the tongue out of operation.

Normally, however, the tongue shoots out in less than the blink of an eye. Prey then adheres to the tongue due to, in part, a suction vacuum effect and a sticky mucus layer on the tongue that acts like super glue. The tongue rolls back into the mouth, carrying the stunned victim with it.

The researchers suspect that toads and salamanders have equally near-weatherproof ballistic tongues.

In the future, the scientists hope that studies on all of these ballistic tongued animals may lead to advancements in prosthetic devices, sports equipment and other objects that often operate using elastic recoil mechanisms.

Anderson says that even walking humans, without device assistance, rely on elastic recoil to improve step efficiency, but the effect clearly isn't as dramatic as a chameleon's speedy tongue.

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