Quetzalcoatlus
Since Quetzalcoatlus was so large, two researchers suggested it was too heavy to fly. This would have been astonishing, because in the whole fossil record there is no flightless pterosaur. It has been thought their mobility on the ground was too poor for them to survive without flight. However, a recent discussion of this idea concluded they probably could fly after all. Another analysis suggested their flight was quite strong. Since we have only a few bones, the question of weight cannot be settled at present.