When alligators assume their half-submerged hunting stance, the hypersensitive bumps along their jaws sense water movements, a biologist has found.

The sensitive detectors may help the killers detect their prey by detecting disruptions at the water surface.

University of Maryland biologist Daphne Soares called the pinpricked-sized holes on alligators and crocodiles Dome Pressure Receptors or DPRs.

To study how the thin-skinned receptors work, Soares looked at how the half-submerged alligators were able to detect a drop of water in total darkness without hearing it.

She found the gators either turned their heads or lunged towards the source to bite it, but only when their faces were on the air-water interface. If the animals were completely submerged or had their heads entirely out of the water, it didn't work.

And when Soares covered the domes with thick plastic, the alligators didn't turn toward the source.

Extinct crocodiles may have hunted dinosaurs

"Our findings show that the alligator is a very touch sensitive creature," said Soares in a release. "Its brain is enormously devoted to DPR information."

Soares strengthened her hypothesis by finding the same pattern of nerves to the DPRs in the jaw bones of fossil crocodiles, which also led a semi-aquatic lifestyle.

The fossil evidence suggests the sensory organ evolved around 200 million years ago in the Jurassic period.

The study appears in the May 16 issue of the journal Nature.