Crocodiles and Alligators Are So Very Touchy-Feely
Whoever came up with the idea that crying crocodile tears means you’re just pretending to show emotion (from the idea that the animals cry to lure a victim and when eating one) really should have learned a bit more about them. From the Journal of Experimental Biology comes a new study suggesting that crocodiles and alligators, for all of their heavily armored, thick skin, have a sense of touch that is “one of the most acute in the animal kingdom.”
Two researchers from Vanderbilt University, Kan Catania and Duncan Leitch, studied the thousands of microscopic pigmented bumps on the two animals’ skins. On crocodiles, the bumps are to be found all over their bodies while the tiny dome organs are found only on the faces of alligators. Using scanning electron microscopy, the scientists found that each spot is densely packed with so many touch sensors that they are even more sensitive to pressure and vibrations than our fingertips.
Scientists have noted the bumps before and called them “integumentary sensor organs” (ISOs). As noted in Science Daily, it’s been speculated that the spots could be used as a “source of oily secretions that keep the animals clean” as well as to detect electric fields, magnetic fields, water salinity and pressure and vibrations.
In 2002, a biologist at the University of Maryland concluded that the ISOs helped alligators to know where single droplets of water were in a darkened aquarium, as they turned their faces towards them even when they were unable to hear due to disruption from white noise. As the ISOs are distributed all over the bodies of crocodiles, Catania thought they might serve another purpose besides detecting water and an extensive investigation of neural connections in tiny sensory spots of American alligators and Nile crocodiles was undertaken by Leitch.
This investigation revealed that nerves that provide sensation to the human face and jaw connect the sensory spots to the alligators’ and crocodiles’ brains. Leitch discovered that the animals have an extensive collection of these “mechanoreceptors” or nerves that respond to pressure and vibration. Some can detect pressure too faint for human fingertips to detect; others can pick up “specially tuned to vibrations in the 20-35 Hertz range, just right for detecting tiny water ripples.” This would allow the animals to detect prey and their location and also to directly, and very quickly, strike.
As for why crocodiles and alligators should have such sensitive skin but also be covered in armor: Leitch and Catania found that the majority of the ISOs were located in the animals’ mouths and near their teeth, the better to help them sense what’s in their jaws. In particular, female alligators and crocodiles use their mouths to break open their eggs when they are ready to hatch and also to carry and protect their young so such sensors in their mouths are more than needed
As Catania says in noting that “massive regions” of our brains are dedicated to processing sensory information from touch: “Crocodilians are not an ancestor to humans, but they are an important branch that allows us to fill in key parts of the evolutionary puzzle for how sensory maps in the forebrain have evolved.”
Other research has found that crocodiles do cry when eating, for physiological reasons. While the cause of their tears is not (as the myth says) sorrow, crocodiles and alligators could be said to literally feel more than we do and to be, indeed, super-sensitive.
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Photo by Tambako the Jaguar