Orcs on both sides

[Alfirin]

Actually since most of the races that Morgoth is credited with "creating" are supposed to be "mockeries" or "perversions" of existing races largely (or solely) on the "good" side, it is entirely possible that Dragons especially the flying kind, were made not merely in mockery of the eagles (as Manwe's beasts of choice, one knows the eagles would loom large in Melkor's mind when the question of "races I need to make" came about) but possibly FROM captured or corrupted eagles. It would seem to be a good start. The only issue I can find with this theory is that one would think that then dragons would have been winged from the first (the only two guesses I can come up with to address this issue is that either the making of dragons was unusually complicated and took more trial and error than most of Melkor's works, that dragon DNA has a lot of variability in it (or why we technically have at least six different kinds if not more) or that "dragon" is best treated as a blanket term for various beasts that, while quite similar in ultimate form and temperament. in fact do NOT necessarily share common ancestry. That is that Melkor found the dragon nature so well suited to his needs (quite possible, given how long it took the armies of the west to find a way of dealing with them) he used the dragon "template" more than once, to various creatures (possibly eagles for the flyers, lizards for the walkers and snakes for the crawlers), and so created the three main draconian races.

[Inziladun]

Originally Posted by Alfirin

That is that Melkor found the dragon nature so well suited to his needs (quite possible, given how long it took the armies of the west to find a way of dealing with them) he used the dragon "template" more than once, to various creatures (possibly eagles for the flyers, lizards for the walkers and snakes for the crawlers), and so created the three main draconian races.

My opinion is that the various breeds of Orcs might have been similarly "made" over millennia using various races of Arda, even though the Elves would seem to be the most likely originals. So I can go along with the idea that dragons might have some differences in makeup, though they plainly share some common traits, most notably in behavior. Both Smaug (flyer) and Glaurung (tail-dragger) had a liking for finding a treasure hoard and sitting on it, and that possessiveness of gold seems to have been a well-known dragon trademark.

[Alfirin]

Originally Posted by Inziladun

My opinion is that the various breeds of Orcs might have been similarly "made" over millennia using various races of Arda, even though the Elves would seem to be the most likely originals. So I can go along with the idea that dragons might have some differences in makeup, though they plainly share some common traits, most notably in behavior. Both Smaug (flyer) and Glaurung (tail-dragger) had a liking for finding a treasure hoard and sitting on it, and that possessiveness of gold seems to have been a well-known dragon trademark.

Scatha (wriggler) had a hoard as well, so it seems universal to the group. The avarice seems to be inherent. In fact Melkor may not have had actually had to add that in, if the legless really originally came from snakes, and the wingless from something like a crocodile/monitor lizard (read Komodo Dragon or Australian Terror Lizard) the greed may simply be what happens when sentience/intelligence combines with their inherent reptilian instincts (there really aren't all that many examples of social reptiles) with a little Melkor wickedness maybe added on as icing.
That also may explain why it took so much longer for the Winged Dragons to make an appearance. If they DID have eagle in their makeup, turning one into a dragon is a heck of a bigger change. To make a snake into a limbless or a lizard to a crawler, all you need to add is size, intelligence, and the ability to breathe fire (for some). To turn an eagle into a flying dragon, you need to extend the tail, replace the feathers with scales, alter the jaws and so on. Lots more work. In fact it might be simple to simply hybridize the eagle into a crawler and hope for the best (or worst). Part of the problem is that, with only about four named dragons (five if you include Chrysophilax), we don't have much to go on with regards to anatomical diversity.
I suppose it is possible the fell beasts are also somewhere in the greater dragon group, though much debased (Smaug is exceptional in size for a Third Age Dragon, but I tend to think even less dragons of them are bigger than a large horse, which is about the size I assume a fell beast is if a human can ride one.) and probably minus a lot of the intellect (they are very clearly animals, not sentients.)