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Among Tetrapods, flight has mainly evolved three times. Firstly among the Pterosaurs - on the front limbs. Then among the Birds - on the front limbs. And finally by bats - mostly dealing with front limbs as the flight control.

So, my question is, given a situation on an alien planet where six-limbed vertebrates happened instead of four, which limbs would be likely to evolve into wings?

My preliminary thoughts on the matter;

It depends on what the limbs become before they turn into wings, I think. Front-most pairs of limbs are most likely given the track record. I can imagine a kind of centaurism happening where the front limbs become specialised for flight in the same pathway as theropod dinos into birds, although I'm not sure how well flight could be developed with two pairs of non-flight limbs behind the flight ones.

Another possibility is that the middle limbs are the ones discarded in favour of a different movement pattern (for a better running gait or something) and they become sexual display features, eventually creating something like a flightless dragon with bright middle limbs that possibly starts developing a wing-flap for primitive flight, or at least gliding/controlled falling?

Do these concepts track and make sense from an evolutionary perspective? Are there other pathways to wings in hexapodal vertebrates that I haven't considered?

Edit for clarification; The vertebrates in question would be a bilaterally symmetrical line of genealogy. I'm imagining the chest cavity/ribs are elongated to make room for a second set of shoulders. I'm considering the possibility of multiple paths towards flight in different lines, since I'm populating a whole world with Hexapods and don't want to limit myself to them evolving flight just once.

(Thanks for the answers, I think this will help me move forward in my building)

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  • $\begingroup$ its assumed in bats and pterosaurs then were using all their limbs as gliders first like flying lemur/squirrels, then specialized to primarily use the front ones . $\endgroup$
    – John
    Nov 5, 2023 at 23:10
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    $\begingroup$ Hello @StarshipVGer, welcome to Worldbuilding. For future reference, please note the following: (a) Providing your own answers (as you did) and expecting more is prohibited (see help center). (b) Per the tour, Stack Exchange is not a discussion forum. (c) You're asking us to speculate. Our only data point for evolution is Earth and there is no science that will let us definitively answer this question. Per the help center, we're here to help you build an imaginary world of your own creation. Therefore, what's stopping you from picking a set of limbs and moving forward? $\endgroup$
    – JBH
    Nov 6, 2023 at 0:29
  • $\begingroup$ Not enough data. Surely it won't be rear limbs, as getting wings would require animals to use rear limbs as feet when taking off or landing. Yet, considering flying squirrels here, both other pair of limbs could evolve. $\endgroup$
    – Vesper
    Nov 6, 2023 at 7:20
  • $\begingroup$ There are no definite rules, and it all depends on eg. what the creature's ancestors were like, and what it is going to do with the wings. Even hind legs can do: the creature could be flying head down, snatching ground-based creatures with its front limbs and jaws if that happens to work best. $\endgroup$ Nov 6, 2023 at 10:13
  • $\begingroup$ I'm pretty sure this will depend on the exact anatomy of the creature. Can you give us details on that? $\endgroup$
    – Joachim
    Nov 6, 2023 at 11:40

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There would be a number of factors that must be considered when determining which set of limbs would evolve to be used in flight. Considering that we are talking about a six-limbed vertebrate-like creature, which is presumably bilaterally symmetrical, we can expect that its limbs will be arranged sequentially along the sides of its body. That said, that's all we know about its limb arrangement at this point. We don't know if these limbs are sticking out to the sides like a lizard's, or tucked beneath the body like a mammal's, or a combination of the two. Why do I bring this up? because a splayed limb is more immediately useful as a wing than a vertical limb.

However, from the point of view of future flight, one of the most important factors is going to be balance. If the wing-to-be is so far forward that the creature would be repeatedly stalling, or so far rearwards that it would simply nose-dive, it's of less use than if it is close to the centre of mass, where pitching is less of a concern.

Of course, with six limbs, we could have fore and aft wings, and a single pair of central legs too... that's probably just as likely as a single pair of central wings and four legs. It might all depend on whether the creature evolved with a need for speed more than flight, which would favour more legs, or flight/gliding more than speed, which would favour more wings.

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So far it has been 100% front limbs adapting into the primary flight structures. So in your case it makes sense that it's the front ones as well.

However you have six limbs, it would be more than cool to have the first two pairs of limbs involved and the third set free and able to do other things.

Bats hindlimbs are constrained as they're part of the flight structure, likewise pterosaurs. Whereas birds can do a lot with their legs as they're divorced from the flight apparatus. Birds use their legs for fighting, walking and lots of other things.

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  • $\begingroup$ "100% front limbs adapting into the primary flight structures" Insects? $\endgroup$
    – James K
    Nov 6, 2023 at 18:07
  • $\begingroup$ @JamesK OP specified vertebrates, so that leaves out insects. $\endgroup$
    – Kilisi
    Nov 6, 2023 at 22:38
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You appear to be under the impression that a wing is supposed to be just a wing

This is not always true: In half the cases of true flight, and the lion's share of unflighted wings, the wings also do duty as a pair of legs

Based on pterosaurs and bats, the most plausible wing arrangement for a vertebrate would be a membrane that encompasses all limbs, with the front limbs bearing wing fingers to extend the membrane leaving the rear limbs as less specialized

In a hexapod, we could see something similar, with the first two limb pairs being wings (as well as legs) and the rear just being feet. There would likely be some level of specialization between the 2 wing pairs: The most plausible option in my view would be that the middle pair would specialize for power generation and the front pair just supporting the leading edge. In this case we could see some centaurism, with the front pair becoming arms/just wings leaving the middle and rear pair as the legs

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