Crocodiles and alligators are notorious for their thick skin and well-armored bodies. So it comes as something of a surprise to learn that their sense of touch is one of the most acute in the animal kingdom. The crocodilian sense of touch is concentrated in a series of small, pigmented domes that dot their skin all over their body. In alligators, the spots are concentrated around their face and jaws. A new study, published as the cover story of the December 2012 issue of the Journal of Experimental Biology, has revealed that these spots contain a concentrated collection of touch sensors that make them even more sensitive to pressure and vibration than human fingertips. "We didn't expect these spots to be so sensitive because the animals are so heavily armored," said Duncan Leitch, the graduate student who performed the studies under the supervision of Dr. Ken Catania, Stevenson Professor of Biological Sciences at Vanderbilt. Scientists who have studied crocodiles and alligators have taken note of these spots, which they have labeled "integumentary sensor organs" or ISOs. Over the years they have advanced a variety of different hypotheses about their possible function. These include: source of oily secretions that keep the animals clean; detection of electric fields; detection of magnetic fields; detection of water salinity; and, detection of pressure and vibrations. In 2002, a biologist at the University of Maryland reported that alligators in a darkened aquarium turned to face the location of single droplets of water even when their hearing was disrupted by white noise. She concluded that the sensor spots on their faces allowed them to detect the tiny ripples that the droplets produced. "This intriguing finding inspired us to look further," Dr. Catania said.
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