Would animals like Plesiosaurs have scales or something else? I was watching X Files and there was an episode about a lake monster and some people were suggesting it was a surviving plesiosaur and they found a scale, but in a lot of illustrations I saw, it looked like they had thick skin
Well the destroyed holotype of Attenborosaurus conybeari breserves smooth skin, while a skin impression on Kaiwhekea katiki has smooth skin regularly studded with low, rounded scales. So the jury is really out. Their closest living relatives are turtles, which is a good source to think about them. However, Plesiosaurs as a group were completely adapted to aquatic life, meaning they may have, for example, lost scales for better streamlining during swimming. Both Attenborosaurus and Kaiwhekea are relatively advanced members of the Plesiosaur group, so phylogenetic bracketing is relatively unhelpful. Hopefully we find more skin impressions of these animals to better complete our picture!