From a different point of view, from flight energetics, Figs. 7 and 8 show the great flight diagram of Tennekes  (quezalcoatlus point added by me). These diagrams clearly show that the points for the pteranodon and the quetzalcoatlus are far from the correlation for all of today's birds, today's insects and today's aeroplanes. To bring these points to the correlation line would require having a significantly higher gas density.
We know of no other scenario which can account for and explain why the metabolic rate of these giant flyers differs from all other warm blooded fliers, and why the flight energetics of pterosaurs is not consistent with all other flyers - from the smallest of insects, to birds and aircraft, all the way to the Boeing 747 (see Fig. 7).