I was browsing the latest issue of Science while kid #3 looks at photos of herself as a baby, and I ran across a short news items about Quetzalcoatlus northrop with a drawing comparing this animal to a giraffe. (sorry, no link) On the other hand, Quetzalcoatlus northrop appears to be much much
ligher than a giraffe, only 70 kg or so. Not clear how this is
supposed to work biomechanically.
I had no idea Quetzalcoatlus northrop was this large. Very odd, you'd think this would be a well known factoid, not just for people like me but for the general public. Or maybe I had seen the 10+ meter wingspan figure and just not realized how big that is, especially for the animal on the ground.
Below an illustration similar to the one in Science. (Ah, also by Mark Witton.)

Also, dimensions via wiki citing Witton and Nash 2008.
Ah, here is Witton and Nash's discussion of Quetzalcoatlus northropi weight estimates, suggesting 70kg is very much at the bottom of the range of weight estimates, which go up to over 200kg:
Drawing
conclusions about the flight of pterosaurs is problematic due to our
limited understanding of their paleobiology. Modelling flight is
particularly difficult for the larger forms due to the lack of
equivalently sized extant analogues [72]:
the absence of such creates problems in estimating the masses of giant
pterosaurs, a critical value in modelling even basic flight attributes
such as wing loading and flight speed. Despite many attempts at
estimating the masses of giant azhdarchids, little agreement has been
achieved. Langston [17] suggested a Quetzalcoatlus with an 11–12 m wingspan may have weighed 86 kg and, with a 15.5 m wingspan, 136 kg. Citing Bramwell and Whitfield's [15] aeronautical work with a lightweight Pteranodon, Wellnhofer [24] suggested that an 86 kg estimate for a 10 m span Quetzalcoatlus could be too high and that its weight may have been comparable to modern ultra-light aircraft. Shipman [76]
suggested that an azhdarchid of similar size would have a mass of 126
kg. The results of a multivariate analysis by Atanassov and Strauss [77] gave mass estimates of 90–120 kg depending on body density, but similar techniques used by Templin [78] and Chatterjee and Templin [16] produced estimates of 62–77 kg, a range of figures also cited by Witton [32]. A similar mass of 70 kg was produced by Brower and Veinus [71] using regression analysis of geometrically modelled pterosaurs. Considerably higher estimates are given by Marden [79] and Paul [73] at 200–250 kg, but calculations by Chatterjee and Templin [16] suggest a pterosaur of this magnitude would never become airborne. These calculations are contradicted by Marden [79], and other workers have criticised lower mass estimates for being impossibly low [66], [73], [80].
It is
noteworthy that all mass estimates of azhdarchids have been based on
methods for which pterosaur soft tissue density has to be estimated.
Many pterosaurs exhibited extensive skeletal pneumaticity (e.g. [31], [81]) and azhdarchid vertebrae and humeri were clearly pneumatised [29], [40].
We therefore assume that azhdarchids exhibited pneumaticity in both
their soft tissue anatomy as well as in their skeleton. However, given
that pneumaticity has been shown to vary considerably among extant
birds [82] and has a significant impact on mass estimates [83],
we know too little about pterosaur anatomy to accurately predict their
masses using density-dependent calculating techniques. A regression
analysis of dry skeletal mass relative to total body mass [84],
a technique that avoids the complications of estimating body density,
generates a mass of 250 kg for a 10 m span azhdarchid, a figure
matching the higher mass estimates of Paul [73], [80] and Marden [79]. Moreover, calculating the body volume of a giant azhdarchid suggests that soft tissue densities have to be less than 0.25 g/cm3
in order to allow masses of under 125 kg (Witton, unpublished data). We
note that the masses of not only giant azhdarchids but all pterosaurs
have been grossly underestimated and suggest that the flight
calculations based on these hyper-lightweight estimates be treated with
caution.
Finally, Witton and Nash's bottom line is that Quetzalcoatlus northropi was a large stork: a terrestrial stalker in high vegetation which flies from feeding spot to feeding spot, unlike storks able to take off by jumping into the air with all four limbs (this proposed mode of take-off was the topic of the news item in Science). Not clear to me how this sort of behavior works if you don't use feathered wings, since damage to the wing membrane is just going to be too common. There are bottom foraging bats that seem to do fine, but they are much smaller.

Update #1: the Vampire bat's all limb take-off, the same -- well, same may be overstating it given size differences -- mode as proposed for Quetzalcoatlus northropi.
Desmodus rotundus jumping.