That some dinosaurs could fly has long been established. That these very same species may have been able to walk--using their wings no less--has been far more controversial. However, the latest computer simulations suggest that the Pteranodon, a pterosaur with a wingspan of up to 25-feet long, while no rapid runner, was able to walk by retracting its wrists so as to walk on its palms. As to why the Pteranodon did so still remains unanswered.
One theory is that walking allowed it to forage for food on the ground. While this idea is enticing, proponents of this theory have yet to propose a reasonable answer as to what led to such a dramatic change in both physiology and locomotion. Another explanation is that flying was the evolutionary advantage conferred upon these creatures: in times of scarcity, a flying creature has access to a far greater abundance of fauna than does one limited to terrestrial movement.