The source of Dragons

[Mariska Greenleaf]

Well it seems settled that Dragons were created by Morgoth, although I would be interested in knowing whether there a definitive source for this, and if so what it is. I strongly suspect that there is, but that I have never come across (or missed) it.

I haven't find it either, mostly it is mentioned that the first one, Glaurung, was first seen in 265 in the first age, coming from Angband. Does this proove him created by Morgoth? You could assume this, but you can't be absolutely certain about it.

I have a question concerning Glaurung: when he was first seen, he wasn't fully grown.
So, if Morgoth "made" him, how so? Did he grow a little one, did he came out of an egg? Maybe this sounds ridiculous, and I'm sorry if it does, but I'm really wondering.

Because it seems to me that al the other evil creatures that were created by Morgoth or Sauron, did not go through the process of growing up. Any thoughts?