Scientists, writing in the Journal of Experimental Biology, say the animals' jaws, covered with small, pigmented bumps that dot their skin, particularly around the face, are extremely sensitive to pressure and vibration, Discovery News reported.
A previous study suggested the bumps -- known technically as "integumentary sensor organs" or ISOs -- detected ripples in water.
"This intriguing finding inspired us to look further," Ken Catania, a professor of biological sciences at Vanderbilt University, said.
The researchers discovered the ISOs contain "mechanoreceptors," nerves that respond to pressure and vibration.
Some are sensitive in a frequency range just right for detecting tiny water ripples, while others respond to levels of pressure too slight for human fingertips to detect, they said.
They are the reason crocodiles and alligators can find prey so quickly, researchers said.
"We didn't expect these spots to be so sensitive because the animals are so heavily armored," study co-author Duncan Leitch said.