When its head was lying along the surface of the water, the animal turned and lunged in the direction of the ripples produced by the droplet. When its head was either fully submerged or completely out of the water, however, the animal ignored the droplet.
In repeated tests, other gators also responded the same way, lunging or at least turning their heads toward disturbances in the water—but only when their stubble of domes was lying along the plane of the water's surface.
Intrigued, Soares then covered gators' domes with a plastic material that diminished their sense of touch. Thus "blinded," the gators ignored water droplets even when their heads did lie along the water's surface.
Hoping to figure out how the domes work, Soares examined alligator skulls to determine what lay beneath the surface of the stubble. The jaws are riddled with small holes through which nerve bundles can relay electrical messages from the domes to the brain.
Ancient Adaptation
Since the nerve-loaded domes represent such an appropriate adaptation to the alligators' stalking habits and their shallow, watery hunting grounds, Soares wondered how long they took to evolve. She discovered that dome pressure points are nothing new—crocodilians appear to have been using them for the past 200 million years.
Soares determined their evolutionary age by examining skulls of various living and extinct crocodilians for the telltale nerve holes. Of 13 different groups of crocodilians she considered, 11 had nerve holes arranged in the same, scattered pattern as the Alligator mississippiensis that first led to Soares' investigation.
Only two crocodilian groups had sparser, and therefore less sensitive, strings of the holes running along their jaws. These animals would have been less effective at hunting half-submerged, Soares thinks.
It's no surprise, then, that one is the oldest known branch of the crocodilians—long since extinct—and the other is an alligator relative that doesn't hunt in the water.
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