I discovered paleoart recently, and I have to say I love it, since I am on deviantart i watch a lot of it. Thanks to it I learn about things I didn’t know existed, and it make me ask myself new questions.
I didn’t find the answer for all of those questions, so I thought maybe I should do artworks in case some cultured people see them and share the answers^^.
The animal drawn here is a Nyctosaurus, a late cretaceous flying reptile. He got the particularity of having a big V horn, which possibly was covered by skin, making a kind of fin. For me this fin really looks like a sail, and made me ask myself if this specie could possibly have evolved to move like a sailboat.
This animal could be a fisher. In drawings I have seen he looked like a marine bird, so water could be in his direct environment. His feet are very short, so I think he would have difficulties to swim, and it could be a good thing for him to find a way to safely rest during the fishing. So, maybe sail power could be what replaced swimming for this specie, if it been the case they could in fact had a behavior very close to some modern marine bird species.
This is how I imagine it: the nyctosaurus is flying over the sea with some of his congeners, he try to find some fish. He does so, wait for conditions to be good, and charges in direction of the water. He enters water, wings along the body. Now his body is just under water in hydrodynamic position, and his sail is over the surface. The wind pushes him, and he earns some speed. He follows a fish and quickly catches it. He can reach the surface, and while he eats the fish, he opens his wings to dry them a little. He is still pushed by the wind, I imagine him earning some more speed and using a wave as a springboard for a fun take off.
I used penguins color because of penguins hydrodynamic and slip skills. I added a fake eye on the sail, because this is a particularity that appeared for a lot of species, and I am very curious to know what a mimic eye like this could have looked like during cretaceous. For example what would an owl butterfly have looked like during cretaceous^^?