Orcs on both sides
 

I just finished reading the Silmarillion again, and during the final chapter, reading about the Last Alliance, I noticed this interesting point; the book says, 'All living things were divided that day, and some of every kind, even beasts and birds, were found in either host, save the Elves only.' This led to me wondering if there were any orcs that maybe rebelled or fought against Sauron, or if anybody had any evidence supporting or disproving this theory? Thanks in advance

Welcome, Ancalagon. An interesting find and question.

I would say that the statement you cite does not include Orcs, as they are not a "kind" as Elves, Men and Dwarves, being corruptions that had over time made a sub-race. At any rate, it's difficult to see any Orcs fighting against Sauron, though I can believe many would have avoided the conflict altogether if given the option.

Actually that statement brings up a lot of questions, as I would imply that there were divisions even among those races of animals that are usually thought to be on one side or the other solely. In other words, Sauron would have to have had Eagles and Ravens, and the Last Alliance would have had to include some dragons and wolves.

Now that I think of it, if you still follow the "Orcs are corrupted elves" line of thought at the time of this writing, even they were divided; the orcs were the "evil" elves.

Alternately, it could be said that maybe that statement was merely a generalization of the "historian", who wanted to get across how polarizing was that war in Middle-earth.

That's an interestimg point, I'd never really thought about it like that considering how separate from eachother, orcs and elves had become by this time.

I think i would have to agree that it was a generalisation in that sense, since 'some of every kind, even beasts and birds' could mean: there were some beasts on each side, and there were some birds on each side, but not necessarily the same type of beast or the same type of bird.

Obviously - I would agree with Inzil that the Orcs, Trolls and dragons and similar "evil monsters" were most likely undivided; they may not get their separate distinction also because they are not real creations, but only perversions of creation, therefore they are not a "kind of living things" by strict definition (and especially Trolls of course are not supposed to be "living things" in the first place, but sort of automata made of stone with some evil will).

It is really notable to point out that there were probably for example evil Eagles on Morgoth's side, but unusual as it is, it is not unimaginable - first, one can easily imagine some individual animals being corrupted or for example possessed by evil spirits such as in the case of Werewolves; second, the very first portrayal of the Eagles in the Hobbit describes them actually as mostly sinister breed, only it is specifically pointed out that these particular Eagles the Dwarves encounter happened, by the sheerest luck, to be the noble Eagles with proud ancestors (as we learn later, coming back to Thorondor and the Eagles of Gondolin).

It's difficult to imagine any Eagles serving Morgoth. If he'd had them, you'd think he could have made some use of them, mainly in scouting and whatnot, and they were supposed to be the eyes and ears in the field on Manwë, as it were. At least it's very hard to see any of them in Beleriand serving evil.

As for those further east, those of the Misty Mountains were said to hate goblins, so they as servants of Sauron were out. If there were Eagles in the East or South, they could conceivably have been removed enough from the West to have been corrupted, but then why weren't they serving as the winged steeds of the Nazgûl? Or, were those steeds "debased" Eagles, ala Orcs?

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.

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.)