It's like a scene from an Aliens movie: a scaly underwater creature looking something like a piranha crossed with a python strikes at its prey which is then reeled deeper into the beast's throat by a second set of toothy jaws.
But this sinister animal isn't a figment of a Hollywood director's imagination, suddenly bursting out of a character's stomach, terrifying audiences. It's a real-life product of evolution.
As if eels weren't already creepy enough, scientists at UC Davis have discovered that some eels have an extra set of jaws deep in their throats that launch forward into their mouths to help pull prey in.
"It looks like a funny pair of forceps with curved sharp teeth," said evolutionary biologist Rita Mehta, lead author of the research, which appears Thursday in Nature.
Mehta and functional morphologist Peter Wainwright captured the odd feeding behavior using high-speed video recordings of eels in lab tanks. Slowed down, the video reveals the jaws coming forward into the mouth and taking hold of a piece of food.
"It was one of those gee-whiz moments when we were absolutely ecstatic," Mehta said. "It was just astounding."
Before the discovery, scientists thought that all aquatic predators swallowed their prey using suction. By dropping the lower jaw and creating a flow of water into their mouths, they draw in the prey. The two species of moray eels studied by Mehta and Wainwright are the first examples of an alternative feeding method.
Bony fish also catch their prey with their teeth, but they still use suction to swallow it.
Instead of sucking, one of these eels bites its prey with its primary set of teeth. It then draws the second set of teeth into its mouth by contracting long muscles. The secondary jaws clamp down on the prey, allowing the eel to move its primary jaws forward in a gulping motion to take in more of the prey. The two sets of jaws take turns until the whole animal has been swallowed.
"It's a mechanical transport system so they can move their prey back into their esophagus," Mehta said. "It allows them to keep a grip on their prey at all times."
Snakes accomplish the same thing by alternately ratcheting the left and right sides of their jaws along their quarry.
Mehta thinks the eels' extra jaws may have evolved to help the eels catch animals in small cracks and crevices in the coral they inhabit. While suction requires expansion of the mouth, the eel's double-jaw trick allows it to remain long and skinny, and may have helped them earn their place as top predator on the coral reef.
The discovery shows that suction feeding in not the final word on fish feeding behavior.
"There are probably more alternatives to suction feeding," Mehta said. "This is probably the tip of the iceberg.
"We're just starting to look."
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