Okay, but in fantasy, there is always the possibility that magic is reinforcing the body and dragons and flying creatures like this, especially the very large ones are often magically enhanced somehow.

Plus in real life we have dinosaurs and pterodactyls and whatnot, which were very large and probably not that fragile, so it wouldn’t be too difficult to envision an alternate planet where dinosaur-like creatures did not die out due to a meteorite striking the planet or anything.