Thks Ruff - a good read.
'Puff the Magic Dragon' is clearly a much more recent carving. The others seem not dissimilar to others found around the world, which I think are sometimes interpreted as impressions of shamanic visions? Surprised - but pleased - the article didn't use the 'glyphs as evidence of alien visitations or that dinosaurs roamed Arizona 2,000 years ago. But I bet Von Daniken's fans would have a field day!
btw I've never seen a real life dragon. But I have drawn pictures of dragons. Why suppose our ancestors lacked the imagination we have today? If we're capable of drawing imaginary monsters then surely our ancestors were able to as well.