Quetzalcoatlus is one of if not the largest animal ever to fly. However, it was also the last Pterosaur to have existed on earth, living up untill the end of the Dinosaurs, living 70 to 65 million years ago. It had a crest at the rear of its massive head, however, the crests size and shape are currently unknown.
When first discovered there was three estimats for its full wingspan. 11m, 15.5m and 21m were all proposed for its size. In 1983 it was lowered to 11-12m wingspan based of newer material from its fellow Pterosaurs. Then at the start of the 21st century a further study was done and with greater knowlage of the Azhdarchids, that Quetzalcoatlus is one of, concluded that its maximum wingspan was 10-11m. In the range of the most conservative early estimate. It may or not be smaller than Hatzegopteryx, who has a 10-12m wingspan.
It was originally proposed that it was a scavenger, like a modern vulture. It would soar high above the ground and land at a carcass to feast on it. In 1996 it this idea was rejected in favour of the idea that it would glide above a body of water and snap at fish while on the wing. Its long neck and beak seemed suited to this Skimming method of feeding, used by some modern birds. This idea was snapped up by the media as a fact, while in reality it had not even been oficially published. A 2008 study into a potential diet for Quetzalcoatlus found that the drag produced by dragging its massive beak through the water was to great to be do-able. Also its skull, jaw and neck anatomy were different to modern day skimming animals. What they did note though was the large size of the back legs compared to other Pterosaurs. This is a feature of Azhdarchids. In fact the fore and hind limb proportions of Quetzalcoatlus are very similar to modern running ungulate mammals, rather than smaller Pterosaurs. It is now believed that they were uniquely suited to a terrestrial lifestyle