Forked Tongues.

On a recent rainy evening, I found myself watching a PBS NOVA special on lizards. Monitor lizards to be exact. (I'm cool like that, I know.)

Monitors are a group of lizards that include Australia's goannas, and komodo dragons, and are more closely related to snakes than any other lizards. Like snakes, monitor lizards have a forked tongue.

Goanna - near Surfer's Paradise, Australia.

While I was watching this special on lizards, the part about the forked tongue made me sit up and take notice, mostly because there was no explanation whatsoever. The narrator tells the audience that "by flicking [the forked tongue] in the air, or touching them to the ground, they pick up scents. Every time they pull in their tongues, they read these scents with an organ in the roof of their mouthes. It's like tasting and smelling at the same time."

... and that's it! The narrator then goes on to tell us the other tracking strategies that the monitor uses, without ever explaining how a forked tongue actually works. We know what it does... but why bother having a fork in it at all?

A forked tongue provides it's bearer a distinct advantage when it comes to smelling things; regardless of whether or not the sense of smell is very acute, it allows the animal to determine very accurately the direction in which a smell came from. When humans smell something, we need to move our entire heads around, and sniff in all directions in order to say "I think the smell is coming from that way" (usually followed by vague, general hand motions). Since we're not very efficient "smellers", we don't rely on this sense as much as our other senses.

Forked tongue on a komodo dragon.
(Picture from Flickr)

Other animals, however, rely on smell/taste for tracking and detecting prey/enemies. With a forked tongue, less effort is needed to determine the direction a scent originates from, because it's like having two noses or tongues at once. Every time the tongue goes in and out, it gathers scent molecules on each side. By comparing the smells gathered on each side, the animal can determine which side has the stronger smell. The left side gathered more scent molecules than the right side? Well the smell must be coming from the left. If it's prey, go left; if it's an enemy, go right. When a snake moves it's head back and forth, it is attempting to gather as much information about it's surrounding as possible. The "organ in the roof of [the mouth]" merely translates the data gathered by the two sides of the tongue.

Explanation oversight aside, it was a great show. Less flashy than the stuff put out by BBC Nature, but I find that NOVA does a great job of highlighting the naturalists and biologists who do the field work that enables us to learn about the animals they showcase. (Also, did you know you can watch NOVA online?)