A hypothesis that bird flight originated with membranous wings

[Halichoeres]

Arguing from scansoriopterygids like Yi qi, these authors postulate that the initial evolution of feathers was as display structures, then exapted for thermoregulation, and only later deployed in flight. The first airborne dinosaurs, in this view, would have flown or glided with membranous wings. THIS HAS NOT BEEN PEER-REVIEWED, it's a pre-print made available online so that it can be improved by comments from the broader community before publication. Open access: https://peerj.com/preprints/27213/

[DinoToyForum]

Arguing from scansoriopterygids like Yi qi, these authors postulate that the initial evolution of feathers was as display structures, then exapted for thermoregulation, and only later deployed in flight. The first airborne dinosaurs, in this view, would have flown or glided with membranous wings. THIS HAS NOT BEEN PEER-REVIEWED, it's a pre-print made available online so that it can be improved by comments from the broader community before publication. Open access: https://peerj.com/preprints/27213/

The comments are pretty scathing.

Flight has evolved independently dozens of times in the animal kingdom because of the significant advantages it provides. So, it seems reasonable to me, on the face of it, that flight could evolve twice independently within Dinosauria.

[Halichoeres]

That's the fun of preprints, right? Anyway when you say dozens of times, you're referring to gliding, correct? I'm only aware of 4 instances of the evolution of proper flight. If scansoriopterygids really represent a 5th, that's a pretty large deal to my mind, although I also don't think that their being capable of powered flight has been demonstrated (correct me if I'm wrong). If they were capable of powered flight, I think it ought to adjust our priors about whether they were on the direct line to birds, in a way that their being "mere" gliders would not necessitate.

[Patrx]

Well, that was an interesting read, and the commentary even more so! It doesn't seem like a very well-supported hypothesis, overall, but I'm sure it will continue to be an intriguing discussion to follow.

[DinoToyForum]

That's the fun of preprints, right? Anyway when you say dozens of times, you're referring to gliding, correct? I'm only aware of 4 instances of the evolution of proper flight. If scansoriopterygids really represent a 5th, that's a pretty large deal to my mind, although I also don't think that their being capable of powered flight has been demonstrated (correct me if I'm wrong). If they were capable of powered flight, I think it ought to adjust our priors about whether they were on the direct line to birds, in a way that their being "mere" gliders would not necessitate.

No, I'm wasn't only talking about vertebrates.

[Halichoeres]

I'm curious what other lineages you mean, then. I'm only aware of birds, bats, pterosaurs, and insects. I'm pretty sure there was only a single origin of flight in insects, and I don't know any other flying invertebrates.

[DinoToyForum]

I'm curious what other lineages you mean, then. I'm only aware of birds, bats, pterosaurs, and insects. I'm pretty sure there was only a single origin of flight in insects, and I don't know any other flying invertebrates.

Oh, I thought flight evolved many times in insects? I stand corrected.

[Vidusaurus]

This seems pretty straightforward and not at all the controversial "hot take" that the comments are making it out to be. I thought it was practically common knowledge that feathers evolved as non-flight structures and were then co-opted for flight capabilities once maniraptors got small enough, given that full wings are known from oviraptorosaurs, ornithomimosaurs and large raptors, all of which were definitely too large to take flight. The only iffy part of this is the concept that scansoriopterygids were capable of powered flight rather than just freefalling/gliding; it's an interesting concept and one which could do with more rigorous testing, but it's not currently very well supported.

[stargatedalek]

The biggest issue here is the idea that flight evolving from a distinct wing structure into another wing structure, that also predates that "first" structure, is more likely than flight evolving twice in closely related animals. We already know flight evolved twice in ornithodirans, I see no reason to rule out the idea that among maniraptorans and early pterosaurs it may have appeared numerous times.

Let alone to go to such lengths just to deny that.

The authors also promote a number of misconceptions (feathers evolving from traditional reptilian scales is an obvious one), and refer to concrete relations in paleontology (such as birds being dinosaurs) as "controversial".

There is one point where I must agree with the implications of the authors statements however, and that is the assertion that wings did not evolve for gliding. Feathers may predate powered flight, but the idea of feathered wings used for gliding is a dated one. Of all the gliding animals known not one evolved into a flying lineage*, and only a handful of gliding animals actually glide using their limbs (and they always use pre-existing structures to do so).

*Microraptor is not a valid example here, as the nature of its locomotion is debated. Some evidence points to powered flight (it gains more lift at higher speed, something not true of known gliding animals). This is also supported by similarly controversial evidence for flight muscle attachments in juvenile Deinonychus.

"Bird-like" wings are incredibly versatile for locomotion, they aid an animal in everything from climbing to balance. The idea that they evolved for anything but locomotion seems ludicrous, but that locomotion was almost certainly not flight, and definitely not gliding.