Hypothetical pterosaur ancestors, or HyPtA, as speculated by Mark Witton in his new book Pterosaurs.
The hypothetical steps start with a Scleromochlus-like leaping little thing with a covering of primitive pycnofibers for insulation. It's already highly active and endothermic, like the first ornithodirans seem to have been.
The leaping lizard evolves into an arboreal animal, sort of an archosaurian squirrel, that also uses it's strong front limbs to grab branches. Then, logically, follows an archosaurian flying squirrel. It only has small membranes, but enough to help it make longer leaps between trees and parachute if it happens to fall. The next step, I think, could be called a reptilian colugo. It's a specialized glider and already more than a bit clumsy on the ground, though it's still not quite capable of powered flight, at least not more than short distances.
And last, the little guy finally taking flight is Preondactylus, which seems to be the most primitive known pterosaur.
The title is actually a quote from the book chapter depicting these animals. Witton's use of language has almost made me snort tea on the pages multiple times. Who said books about science are boring?
No doubt the actual story, if we ever find the fossils to tell it, is a lot more messy and confusing. At least bird evolution still is full or mysterious stuff even though we know dozens of transitional species. But this is a neat little hypothesis to compare future fossils to. And it includes ridiculously cute little animals.