Of those animals, two are virtually sister taxa, one might not actually have sails, and the last two have interesting sail shapes. Dimetrodon and Edaphosaurus have wimpy rounded neural spines, while all of the archosaurs on the list (save Amargasaurus) have flat (side to side) but wide (front to back) neural spines. Surely there's a reason for these differences.
But that's not even the point. If sails evolved to soak up heat, why didn't they evolve several times? Isn't it more parsimonious (as they say) to conclude that sails have a display function first, and a heat-soaking function second?
Bah--I probably don't know what I'm talking about.
Thanks to fellow NWR colleague Aaron Kaluszka for teaching me the HTML tags for bullet points. Now I feel smarter!