Actually, I can vouch for KP on Tyrannosaur growth.

That, is a chart of growth for various Tyrannosaurs. T-rex is the black line, and has the most pronounced growth.
As for the Quetzalcoatlus issue... both the light-weight bones and the air bladders are probably remniscent of when their kind did fly.. before they got too heavy...
As for my theory on how they defended themselves... it goes like this. (Please note that, since this is dealing with extinct animals, there's no scientific proof to go with this, and is simply educated guessing at best.)
Let's suppose that a trio of Quetzalcoatlus are moving along the plains, searching for lizards. Nearby, there's a herd of Tricerotops grazing on some shrubbery, and a bunch of Pachys fighting over mates. In the shadows, a young, 17 foot Tyrannosaur has its eyes set on a baby Triceroptops, at the edge of the herd.
But as the predator preapres its attack, it steps on a twig, the sound aleting the sharp ears of the Quetzalcoatlus, who whirls its head around to face it. It then lets out an ear-splitting screech that the other two Quetzalcoatlus join in. The noise is incredibly painful to the T-rex, who reacts to it like it's recieved a physical blow. Unfortunately for it, the incredibly loud screeching not only serves as a detterent to predators, but as an alarm call to other herbivores. The trikes immediately form into defensive formation, all of them barking and grunting at the T-rex. The pachies too get into defensive formation, and the Rex, realizing it's lost a potential meal, and unable to take the horrible noise, slinks off, heading for a nearby forest...
that, atleast in my mind, is probably how Quetzalcoatlus defended itself... unfortunately, there's no proof it did anythin glike that, but with dead animals, speculation is all a Scientist can do...