So I am finishing up a functional concept of an alien I have been working on (a large semi-aquatic amphibian) and I am at the final piece of the puzzle. Their sails.
I wanted these creatures to evolve spinal sails but didn't have a use for them yet (which I later came up with a way to incorperate it into how they use wasted energy and food). But I am curious if they would have a use for two more sails on its side, close to the center of the spine then going out diagonally but I am having trouble as to a possible use for said sails. If used for display it would probably use the larger, central sail for that so I'm curious to see other possibilities for this evolution... if possible.
Edit: Thank you everyone for all the suggestion. Some pointed out the sails could be for heat, some for movement, and others for just sexual attraction. But in the end I decided to turn their sub sails into a super respiration system. Thank you all once again.