Have there been any sightings of dragons?

Gryphons are not and have never been real creatures. There is, however, mounting evidence that the ancients stumbled upon the fossil remains of a Ceratopsian dinosaur and mistook it for a giant winged quadroped.

If the frill on a ceratopsian (especially one with large holes in it) were smashed and spread over the back, combined with the beak-like face, pointed front toes and flat back feet, I can see the skeletal resemblance.