Alligators can detect the slightest ripple in the water
The animals can hunt without sight, sound or smell using sensors on their jaws that detect ripples in the water.
When prey enters the water, perhaps to take a drink, the alligator or crocodile is able to sense even the slightest movement and pounce.
Even a single droplet falling into a tank the size of a bath can be sensed by the network of pressure detectors on the creatures' jaws.
Jurassic beginnings
The sensors, about the size of a pinhead, are dotted around the animal's face like a beard.
The marks look like tiny pinpricks. Alligator and crocodile experts have noticed them before but have not been able to fully explain the marks.
All living alligators and crocodiles have the small holes, as do some of the family's fossil ancestors.
The biologist behind the latest research, Daphne Soares, thinks the sensory system evolved millions of years ago, when primitive crocodiles shared the Earth with dinosaurs.
"Evidence shows that this sensory organ may have appeared around 200 million years ago, in the Jurassic period," says the University of Maryland scientist.
"It's fun to imagine these enormous extinct crocodiles sitting half way submerged in the water at night, waiting for dinosaurs to come and drink.
"Just at the moment the dinosaur broke the water surface with its mouth, it would have sent pressure waves in the water, telling the crocodile where to get its next meal."
Ms Soares has named the sensors dome pressure receptors.
In the dark
They only work when the animals are half under the water.
Lab experiments show that alligators can still sense water disturbances when their eyes, ears and noses are covered.
When the bumps are covered with a layer of plastic jelly, the alligators are unaware of any movements in the water.
The alligator research is published in the journal Nature.
Images courtesy of crocodilian.com.