Ever since pterosaurs were discovered, theories of all shapes have been formed to speculate on how, if, or when pterosaurs could fly. Recent theories speculate that juveniles almost right after hatching may have been able to fly, but by far the most debated theory has been the shape of the wings. Here is Sordes pilosus
, a pterosaur that has been at the center of the debate due to the well-preserved holotype, which suggests a tissue that stretched from each of the hindlegs to the wing tips, illustrated here as Sharov's View. This old-school interpretation was prevalent for decades before Sharov, however, as even Harry G. Seeley discussed this on pterosaurs from Solnhofen, Germany, and the Liassic beds of Dorset, England, where only a broad-chord wings were capable of allowing the animal to fly at all.
(Chord is the measure of the distance from the front margin of the wing to the rear margin, compared to the span of the wing. A broad-chord wing has a more even ratio [closer to 1] than narrow-chord wings [further from 1].
Newer debate however has argued that the hindlegs are not, in fact, so intimately related to the wings, but that the membrane from the legs stretched between the legs and contacted the tail, but not the wing membrane. This was argued by Kevin Padian from Berkeley, and is termed here the new-school version. The wing membranes extend from the sides of the body to the tips, not from the legs, and the design is narrower in the chord. What is surprising is that Sordes
is ambiguous in the shape of the wing membrane, as the margin from the wingtip to the leg (or wingtip to the body wall) is actually not present on the fossils known. But the margin of the membranes around the feet are well-preserved, and show that the fifth-toe is the base of both versions. The argument is wether this toe extends the membrane to the wings, or between the feet themselves, and this may depend on a positional argument of the feet themselves: Does the foot show the ability to extend the toe sideways, dorsally, ventrally, or even towards the tail to allow the membrane to connect to the tail? Fortunately, I don't have the answer that here