The eel can then open its front jaws, releasing the prey, while the pharyngeal jaws move back down into the throat, dragging the food with them.
"It seems that almost everyone we showed the movie to said 'My God, it's like Alien," Wainwright said. "It really does have this monster-from-outer-space feel to it."
Mehta and Wainwright published their results in the current issue of Nature.
As strange as moray jaws may seem, Mehta sees their evolution as just a matter of tinkering with standard fish anatomy. One central step in the transition, Mehta proposes, was the loss of the front fins. The bones that once supported those fins could now take on a new role, anchoring muscles to help move the pharyngeal jaws. The other muscles that move the jaws have the same attachments found in other fish. But in the moray, some have become bigger or longer.
Shifting from suction-feeding to an alien bite may have helped turn morays into the top predators they are today. Suction works well for catching small fish, but big prey can escape the inflow of water.
To use suction, a fish has to expand its head, which can be difficult in the narrow crevices where morays often hunt.
A biting set of pharyngeal jaws, on the other hand, may have allowed morays to catch larger prey. Its front set of teeth needed only to grab onto part of an animal and hold it in place for about half a second while its pharyngeal jaws moved forward into the mouth. Now it could eat fish that were bigger than its gape.
Mehta is investigating other fishes to find clues to how the moray's double bite evolved. So far, she knows of no other animal that feeds this way. At least on this planet.
H.R. Giger, the Swiss artist who created the alien for the director Ridley Scott, was amused by the researchers' discovery.
"It's funny," he said. "The double teeth came when I did my first drawings. Ridley Scott told me to make it so that it could move. I hadn't studied any animal. My instructions were that it should be somehow frightening and horrible, and I did my best."
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