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RE: When narwhals (Monodon monoceros) rub their tusks together, it is believed to be to share information about the water, not as a sign of aggressive rivalry
I wonder why the "probe" would need to be external. It seems like a large probe that seems to offer little benefit over some internal or skin sensor. Maybe it's multifunctional defence plus probing.
That's a good question. While you might be right about the multifunction of the horn, here's what I believe is the reason why this sensory organ is in the shape of a horn, and not in the skin itself.
As you can read in the research paper I linked to, the horn is extremely sensitive, which is probably necessary for picking up the salt concentration change. Since the narwhal lives in very cold water, they need lots of fat between the skin and the organs to stay warm, so it would most likely be very difficult to have such sensitive sensors there. A horn gives them a huge surface area to pick up on the salt concentration, while having a very small contact point between the body and the horn, minimizing the amount of heat that gets lost due to this organ.
The most of this is my own hypothesis, so it might of course be wrong, and there could be an entire different reason ;)
I tend to agree with your hypothesis. As a defensive weapon, a horn that long seems unwieldy, when compared to the much more versatile claws and teeth other animals have at their disposal.
Yep, that's a good point. It would probably be very inefficient for hunting and dueling with.
I never thought of that. I wonder if there is a correlation between animals with lots of fat/blubber and having less sensitive skin? It does seem efficiecient to have a large surface area with little contact to the body for heat preservation.
Good question! I would assume so. While our own nerves are in the top layer of our skin, I don't see why this would make any sense for animals that often get exposed to uncomfortable situations (such as whales who swim in almost freezing water). Sadly I'm not very knowledgeable about animal physiology / anatomy, so I can't really answer you. Sorry!
@valth your sensor hypothesis seems logical and I convincing...