Crocodile and alligator jaws, along with the pigmented bumps on their bodies, are more sensitive to pressure and
vibration than human fingertips, according to a new study in the Journal of Experimental Biology.
Their sense of touch is among the most acute in the entire animal kingdom.
The study sheds light on the function of the small, pigmented domes that dot their skin, particularly around the face. I always thought these freckle-like features were for camoflauge, but they turn out to be much more complex.
"We didn't expect these spots to
be so sensitive because the animals are so heavily armored," co-author Duncan
Leitch said in a press release. Leitch, a graduate student, performed the studies under the
supervision of Ken Catania, a professor of biological sciences
The technical name for the spots is "integumentary sensor organs" or ISOs. Scientists over the years have speculated that they held all kinds of functions, from secreting oil to detecting electrical fields. A study in 2002, however, suggested that they detected ripples made by water, so that led to the latest research.
"This intriguing
finding inspired us to look further," Catania said. "For a variety of
reasons, including the way that the spots are distributed around their
body, we thought that the ISOs might be more than water ripple sensors."
After ruling out a bunch of functions, the researchers discovered that the ISOs contain "mechanoreceptors," which are nerves that respond to pressure and vibration. Some
are specially tuned to vibrations in the 20-35 Hertz range, just right
for detecting tiny water ripples. Others respond to levels of pressure
that are too faint for the human fingertip to detect.
This helps to explain how crocodiles and alligators can find prey so quickly, directing their strong jaws and sharp, big teeth in just the right direction for the death snap.
The most
heavily wired ISOs are located in the mouth near the teeth. Crocs and gators use their teeth for many different things. Females, for example, delicately break open their eggs when they are ready to hatch. They also carry their hatchlings in their jaws, the same ones that can clamp down on
prey with incredible force.
The sensitivity then permits such diverse actions. It also, I think, gives many species a cool speckled look. Unfortunately people like this style too, on handbags, shoes, luggage. Better to admire it on the living animal.
(Images: Steven Green, Catania Laboratory/Vanderbilt University)
