Nature and origin of dragons

[Tuor of Gondolin]

From some references to dragons in Middle-earth writings, and comments such as an old " Hobbit" thread "Dragon Info", started Dec., 24, 2002, it seems to me there are two possible explanations for the origin of dragons, both of which have problems.
1---they were maia (like balrogs)
2---they were a twisted race (like orcs)

If maia, then why is it said that Morgoth (taking a long time to achieve it) "twisted them", wouldn't it have been a voluntary decision to make themselves incarnate?

If a twisted "race", then where did they come from? Morgoth could not create life, and dragons could not come from kelvar, and presumably could not come from elves, men [hobbits are related to humans], ents, or dwarves. So what then would the origin of dragons be?

The only possible "loophole" I can see is the eagles of Manwe, if you accept Robert Foster's view in the complete guide to Middle-earth "Apparently the Eagles of Manwe are the highest of the Kelvar, just as the Ents are of the olvar." So perhaps dragons are corrupted Great Eagles? But I had the impression that the predominant view is that the Eagles are maia.