Do crocodiles co-opt their sense of “touch” to “taste”? A possible new type of vertebrate sensory organ

We recount here two experiments carried out which suggest the existence of the first described integumentary osmoreceptor of its kind in a vertebrate. Domed pressure receptors, present on the cranial scales of alligators have previously been demonstrated to convey the sensation of “touch” when flattened by pressure. Here we find that morphologically similar domed sensory organs present on the post-cranial scales of crocodylid but not alligatorid crocodilians flatten when exposed to increased osmotic pressure, such as that experienced when swimming in sea water hyper-osmotic to the body fluids. When contact between the integument and the surrounding sea water solution is blocked, crocodiles are found to lose their ability to discriminate salinities. We propose that the flattening of the sensory organ in hyper-osmotic sea water is sensed by the animal as “touch”, but interpreted as chemical information about its surroundings.