It just makes so much sense you wonder why you've never thought of it before, ehh? My setting is very wild-west/Victorian inspired, and one of the first thoughts I had was "If cowboys and carriages didn't have horses to draw them. . . what might they use?" and so I came to the conclusion that at least in parts of this world, dragon-like creatures became one of the dominant life forms, possibly evolving out of a large bat-like creature. I like the idea of a non-reptilian dragon with the sort of natural fleshy armor as Rhinos and the like(to a higher, and more finely tuned degree of course.)