# The Feathered Dinosaur. **URL:** \ **Category:** Great Debates\ **Created:** [April 26, 2001, 11:46pm UTC](https://boards.straightdope.com/t/the-feathered-dinosaur/63457 "2001-04-26T23:46:18Z")\ **Posts on this page:** 14\ **Page:** 2
**Author:** ![Darwins\_Finch](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darwins_finch/32/20304_2.png) [@Darwins\_Finch](https://boards.straightdope.com/u/Darwins_Finch)\ **Post date:** [June 19, 2001, 12:45am UTC](https://boards.straightdope.com/t/the-feathered-dinosaur/63457/21 "2001-06-19T00:45:47Z")
> [@](#): > > \*Originally posted by Mangetout \* > \*\*…can someone propose a sequence of events that could have resulted in useful wings developing as a gradual process? The sequence of events would probably differ depending on the type of wing we are talking about. Pterosaurs and bats, for example, have wings made of stretched membranes between each finger and the body (in the case of bats) or between a single finger and the body (as in pterosaurs). It is not difficult to imagine gliding precursors to these sorts of wings. For bird wings (the feathered kind - even though they, too, possess membranes linking the upper and fore-arm, as well as the upper arm and the body), the sequence of events depends on whether you accept the “ground up” or “trees down” theory of the origins of flight. > [@](#): > > so at each stage of development, the proto-wings must represent an advantage of some kind, even though they didn’t yet bestow the ability to fly. \*\* This is not entirely accurate. A given structure will not be selected against simply because it does not bestow an evolutionary advantage to an animal. It need only not incur a _disadvantage_. An advantageous structure will likely be selected for, a disadvantageous one selected against, but a non-advantageous, non-disadvantageous one would essentially be “invisible” to natural selection. However, these neutral structures could then later be co-opted to a functional, advantageous use. ---
**Author:** ![Badtz\_Maru](https://avatars.discourse-cdn.com/v4/letter/b/e36b37/32.png) [@Badtz\_Maru](https://boards.straightdope.com/u/Badtz_Maru)\ **Post date:** [June 19, 2001, 4:00am UTC](https://boards.straightdope.com/t/the-feathered-dinosaur/63457/22 "2001-06-19T04:00:18Z")
> [@](#): > > \*Originally posted by Mangetout \* > \*\*Not that I particularly want to argue on either side of the Creation/Evolution debate, but can someone propose a sequence of events that could have resulted in useful wings developing as a gradual process? > > i.e: the end result (flight) wasn’t predetermined in any way; Evolution didn’t ‘know’ where it was heading, so at each stage of development, the proto-wings must represent an advantage of some kind, even though they didn’t yet bestow the ability to fly. \*\* I’ve heard a couple of theories on what wings were originally. They may have started out simply as display devices, or been useful for catching flying insects, but I think the idea that makes most sense is that they developed the feathers as some way of keeping balance and/or adding maneuverability in a semi-arboreal setting, which lead to some bird ancestor making longer and longer jumps from branch to branch, initially gliding like ‘flying squirrels’ and eventually flapping. ---
**Author:** ![Darwins\_Finch](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darwins_finch/32/20304_2.png) [@Darwins\_Finch](https://boards.straightdope.com/u/Darwins_Finch)\ **Post date:** [June 19, 2001, 7:22am UTC](https://boards.straightdope.com/t/the-feathered-dinosaur/63457/23 "2001-06-19T07:22:51Z")
> [@](#): > > \*Originally posted by Badtz Maru \* > \*\*…I think the idea that makes most sense is that they developed the feathers as some way of keeping balance and/or adding maneuverability in a semi-arboreal setting, which lead to some bird ancestor making longer and longer jumps from branch to branch, initially gliding like ‘flying squirrels’ and eventually flapping. \*\* Except the hind limbs of early birds like _Archaeopteryx_ were better suited for terrestrial environments than arboreal ones. While the structure of the claws on the forearm indicates that arboreality was possible, the general structure of the animal does not fit an arboreal profile. The generally accepted “ground up” sequence works similarly to what you describe, **Badtz** , except instead of leaping from branch to branch, they take progressively longer horizontal leaps (with the aid of feathers better suited for achieveing lift, as opposed to merely providing insulation, as well as rudimentary flapping for stability), eventually achieving a sort of flapping flight. [Here](http://www.freethought-web.org/ctrl/news/file013.html) is one article which addresses this in further detail. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [June 20, 2001, 2:44pm UTC](https://boards.straightdope.com/t/the-feathered-dinosaur/63457/24 "2001-06-20T14:44:13Z")
> [@](#): > > \*Originally posted by Darwin’s Finch \* > \*\* > > > [@](#): > > > > so at each stage of development, the proto-wings must represent an advantage of some kind, even though they didn’t yet bestow the ability to fly. \*\* > > This is not entirely accurate. A given structure will not be selected against simply because it does not bestow an evolutionary advantage to an animal. It need only not incur a _disadvantage_. An advantageous structure will likely be selected for, a disadvantageous one selected against, but a non-advantageous, non-disadvantageous one would essentially be “invisible” to natural selection. However, these neutral structures could then later be co-opted to a functional, advantageous use. > \*\* Sure, but even something as seemingly neutral as a web of loose skin (that might later evolve into a flight membrane), if it doesn’t convey a definite advantage, must carry some sort of disadvantage, however minor, for example: [list=1] [li]Infection (flappy webs of skin are going to be more prone to damage than tight-fitting skin)[/li][li]Mechanical hindrance (if your forelimbs have embellishments on them, they may not be as much use as forelimbs in their own right).[/li][li]Aerodynamic drag (if your wings haven’t evolved enough to be useful for even partial flight, then running away from a predator whilst carrying them is going to slow you down)[/li][/list=1] To name but three - even the very smallest disadvantage due to excess baggage should result in a selection against it. Don’t get me wrong here, I’m not arguing about whether it **has** happened, I’m just very puzzled as to how it **did**. The ‘wings as display devices’ is the one that comes closest to convincing me so far, given the abundance of display behaviour in reptiles and birds today. ---
**Author:** ![Tars\_Tarkas](https://avatars.discourse-cdn.com/v4/letter/t/6a8cbe/32.png) [@Tars\_Tarkas](https://boards.straightdope.com/u/Tars_Tarkas)\ **Post date:** [June 20, 2001, 7:45pm UTC](https://boards.straightdope.com/t/the-feathered-dinosaur/63457/25 "2001-06-20T19:45:38Z")
> [@](#): > > Mechanical hindrance (if your forelimbs have embellishments on them, they may not be as much use as forelimbs in their own right). One job feathers probably had pre-wing was to help as a “net” to catch bugs, while the dino still had the claws on the ends for running up trees and gripping. > [@](#): > > Aerodynamic drag (if your wings haven’t evolved enough to be useful for even partial flight, then running away from a predator whilst carrying them is going to slow you down) Dinos can always put their arms to their sides, plus feathers are lightweight, and can pull off if grabbed without damage to the body, and would be easily replacable. The feathers would still make the dino look bigger, but allow decreased body mass, allowing less food to be needed, which is a good thing. And you never know about that display device thing, either. (stupid fossils, fossilize while in a coutship display already!) ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [June 20, 2001, 10:00pm UTC](https://boards.straightdope.com/t/the-feathered-dinosaur/63457/26 "2001-06-20T22:00:57Z")
> [@](#): > > \*Originally posted by Tars Tarkas \* > **One job feathers probably had pre-wing was to help as a “net” to catch bugs, while the dino still had the claws on the ends for running up trees and gripping.** I find this somewhat hard to swallow, perhaps I’d have an easier time if there was a modern-day animal that filled the same niche (i.e. running around and netting bugs with modified limbs), but I can’t think of one, (or is it that the niche no longer exists as such, as predation of insects is pretty well covered?) I don’t have a problem with the idea of feathers developing from scales for warmth, that much seems fairly simple, it’s the idea of superficial proto-wings, I’ve yet to see a _very_ convincing explanation. ---
**Author:** ![Darwins\_Finch](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darwins_finch/32/20304_2.png) [@Darwins\_Finch](https://boards.straightdope.com/u/Darwins_Finch)\ **Post date:** [June 20, 2001, 10:12pm UTC](https://boards.straightdope.com/t/the-feathered-dinosaur/63457/27 "2001-06-20T22:12:32Z")
> [@](#): > > \*Originally posted by Mangetout \* > **Sure, but even something as seemingly neutral as a web of loose skin (that might later evolve into a flight membrane), if it doesn’t convey a definite advantage, must carry some sort of disadvantage, however minor, for example: > [list=1] > [li]Infection (flappy webs of skin are going to be more prone to damage than tight-fitting skin)[/li][li]Mechanical hindrance (if your forelimbs have embellishments on them, they may not be as much use as forelimbs in their own right).[/li][li]Aerodynamic drag (if your wings haven’t evolved enough to be useful for even partial flight, then running away from a predator whilst carrying them is going to slow you down)[/li][/list=1] > To name but three - even the very smallest disadvantage due to excess baggage should result in a selection against it.** The arms of proto-birds could be folded very tightly against the body, very much as a bird’s wings do when the bird is at rest; the loose skin flaps (which were more likely elastic skin flaps - again, much like those in birds) were not likely to be in the way at all. Also, in all likelihood, these flaps were covered by feathers, so had some extra protection against injury. During the evolution of true flight, the proto-birds’ arms _were_ becoming less useful for grasping. The forearms were increasing in length, the number of fingers were being reduced, etc. The claws were maintained, since even with more limited mobility in the arms, they could still be used for grasping or perhaps climbing. > [@](#): > > **One job feathers probably had pre-wing was to help as a “net” to catch bugs, while the dino still had the claws on the ends for running up trees and gripping.** Feathers, in general, don’t make good bug catchers. At best, they might swat the bug around, but it is unlikely they would have been able to trap anything. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [June 21, 2001, 11:08am UTC](https://boards.straightdope.com/t/the-feathered-dinosaur/63457/28 "2001-06-21T11:08:05Z")
> [@](#): > > \*Originally posted by Darwin’s Finch \* > **The arms of proto-birds could be folded very tightly against the body, very much as a bird’s wings do when the bird is at rest; the loose skin flaps (which were more likely elastic skin flaps - again, much like those in birds) were not likely to be in the way at all. Also, in all likelihood, these flaps were covered by feathers, so had some extra protection against injury.** This still doesn’t bring me any closer to understanding why the flaps were there at all, if they weren’t yet useful for flight - I understand your earlier point about them maybe being of neutral value, but I can’t bring myself to accept that such a noticeable change in form could have absolutely **no** impact, favourable or otherwise. It’s also quite a stretch of the imagination to believe that gradually, over the course of many generations, skin flaps developed for no particular reason other than they weren’t **un** necessary. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [June 21, 2001, 11:14am UTC](https://boards.straightdope.com/t/the-feathered-dinosaur/63457/29 "2001-06-21T11:14:53Z")
Although actually, if we’re talking about skin flaps, then we’re really discussing the evolution of bats, flying squirrels and pterosaurs; birds (at least the ones i’ve seen) don’t really have skin flaps at all; they have relatively skinny arms covered with rigid, ordered flight feathers. - It’s much easier to accept that these might have originally developed to quite a size for the purposes of insulation, at the same time as becoming nicely ordered and enlarged/rigid for courtship displays, at which point they _could_ concievably start to be useful as brakes/rudders while running, and then onwards to aids for extending the length of jumps and so on. ---
**Author:** ![Darwins\_Finch](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darwins_finch/32/20304_2.png) [@Darwins\_Finch](https://boards.straightdope.com/u/Darwins_Finch)\ **Post date:** [June 21, 2001, 11:29pm UTC](https://boards.straightdope.com/t/the-feathered-dinosaur/63457/30 "2001-06-21T23:29:14Z")
Modern birds do possess ‘flaps’ of skin which stretch between the wrist and body, along the anterior edge of the wing. This is what makes the leading edge relatively straight - necessary because the arm bones themselves cannot ‘straighten’; they are always bent, even when the wing is fully extended. The elasticity of this membrane allows the leading edge to maintain its integrity, so to speak, during the full range of motion of the wing. Usually, they are covered with feathers and are not noticeable. [aside] I have a cockatiel which has the bad habit of plucking her feathers, and the complete underside of her wings are bald. As a result, this membrane is very noticeable on her! [/aside] So, wing membranes are common to all three groups of vertebrate fliers. The structures may differ, but they _are_ present. As to how these might have evolved, and for what original purpose (if any)…I couldn’t tell you. Unfortunately, avian evolution is not one of my specialties. Although, it does seem reasonable that the evolution of this ‘leading edge membrane’ was critical to the evolution of flapping flight since without it, the wings would likely be less efficient airfoils. ---
**Author:** ![Darwins\_Finch](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darwins_finch/32/20304_2.png) [@Darwins\_Finch](https://boards.straightdope.com/u/Darwins_Finch)\ **Post date:** [June 21, 2001, 11:35pm UTC](https://boards.straightdope.com/t/the-feathered-dinosaur/63457/31 "2001-06-21T23:35:57Z")
Of course, after I made my last post, I thought of something: because of their elasticity, it could be that the original purpose of the aforementioned wing membranes might have been to keep the arms folded against the body when at rest. This would keep them out of the way, and might even have aided in insulating the body when resting, without having to expend extra energy to keep the arms folded. ---
**Author:** ![Triskadecamus](https://avatars.discourse-cdn.com/v4/letter/t/b19c9b/32.png) [@Triskadecamus](https://boards.straightdope.com/u/Triskadecamus)\ **Post date:** [June 22, 2001, 12:29am UTC](https://boards.straightdope.com/t/the-feathered-dinosaur/63457/32 "2001-06-22T00:29:52Z")
Flaps of skin depending from limbs which are gradually less involved in bipedal locomotion might have developed to allow rapid absorption of warmth from the sun, and rapid dispersion of the heat generated by muscle motion. For this function, the more aerodynamic the flaps, the less they interfere with motion, and the better they cool the body during running. The ability to lean further foreword into the resistant air is beneficial as well, and reduces the need to support tissue for a counterbalance with a large tail. Flaps that can be moved through limited configurations can also provide gains in agility for changes of direction during bipedal motion. At some point it becomes a beneficial factor if there is some tendency toward lift, which can increase the speed, and endurance of the runner. That characteristic tends to place more benefit from upper body musculature, which bipedal locomotion has made non-beneficial. Different body shapes have different advantages, but do not require flight at any point until an already aerodynamic wing structure is already nascent. This is not mount improbable, it barely qualifies as a bunny slope. ## Tris “I believe in general in a dualism between facts and the ideas of those facts in human heads.” ~ George Santayana ~ ---
**Author:** ![clayton\_e](https://avatars.discourse-cdn.com/v4/letter/c/c57346/32.png) [@clayton\_e](https://boards.straightdope.com/u/clayton_e)\ **Post date:** [June 26, 2001, 5:33am UTC](https://boards.straightdope.com/t/the-feathered-dinosaur/63457/33 "2001-06-26T05:33:14Z")
How about that one that has the visable organ impressions? Pretty cool. ---
**Author:** ![Homer](https://avatars.discourse-cdn.com/v4/letter/h/df788c/32.png) [@Homer](https://boards.straightdope.com/u/Homer)\ **Post date:** [June 28, 2001, 2:16am UTC](https://boards.straightdope.com/t/the-feathered-dinosaur/63457/34 "2001-06-28T02:16:18Z")
How are the rear legs structured? Is it conceivable that the proto-avian herbivore ate food from the trees, and jumped from the surface to the limbs, and as the dinosaurs in general evolved larger and larger, as did the trees, and the proto-avians had to jump further and further until flight was a necessity? A proto-avian with feathers, hollow bones, or skin flaps would be better suited for further and further jumps, until the skin-flap forearms were able to provide some small amount of lift. Fast forward millions of years, we got birds. –Tim [Previous page](https://boards.straightdope.com/t/the-feathered-dinosaur/63457.md?page=1)