Who is the dragon?

Yesterday morning I found this beside the paddock.

Dragon scale

And in my slightly tired morning eyes it shimmered like a dragon scale. This mysterious glimmering green ...
So who of my three friendly hairy creatures is the one which changes secretly in a dragon and flies around?
I checked all of them for evidence but couldn't find one.
My chief suspect is Moritz, it's always him, he has the most creative mind, is too easily bored and is Mr Understatement in person. Also I really can imagine him as a dragon.

Magic sky: Two rainbows

And in the evening, at the morning when I had found the scale, we had two rainbows, which stand like a big magic sign in the sky. So all is possible, even Moritz changing by night in a dragon. Usually there are werewolves: I have dragons. Yes, the plural, because finally I came to the conclusion that all three are changing. It has to be all of them ... So, now I'm waiting for the invitation ...
But I run with my ponys, I'm a PonyRunner, so I heard about Dragonriders, but has anyone ever heard about a DragonRunner?