Why did dinosaurs evolve feathers?

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A common creationist canard is the supposedly unanswerable "what use is half a wing?". Apparently there to confound biologists, what it generally does is demonstrate the ignorance of the asker with respect to evolutionary theory. However, the actual broader question that is inferred – what use is a feather to a non-flying bird? – is both relevant and interesting.


The earliest filamentous feathers appeared in dinosaurs well before birdsever did, and were present in plenty of species that had no hope of taking to the air (though I for one would love to see a flying tyrannosaur). So then, what might their original function have been, and what prompted them to be maintained, grow larger and change over time? The exact answer is sadly unknown. It is likely a number of factors in concert, or different ones having greater importance over others at various times, and piecing those fragments together is very tricky. However, there are some strong leads and ideas, and for some feather types in some groups the answer is rather convincing.

To deal with the central issue though, there are in fact various things that feathers may offer animals aside from flight alone. A quick look at living birds reveals plenty of possibilities, and almost all of them may be applied to various (or even all) dinosaurs that preceded true, powered flight. There really are quite a few, so I'll try to be brief, but it shows just how many selective pressures may have acted on feathers and led to their spread and development across the various dinosaurs that had them.

Most obviously, there's temperature regulation. Birds typically maintain a high body temperature and so keeping that heat in requires some form of insulation. While it's uncertain as to the physiological state of various dinosaurs at least some were almost certainly bird-like in metabolism. Even those that were not might still have benefited from insulation (see also fuzzy things with odd physiology like the platypus and moths) so that doesn't rule it out, and of course they could also use these feathers to insulate eggs or young animals, and we do know many dinosaurs were good parents and even brooded on nests. Similarly, feathers can help keep things cool by providing shade (again, eggs and babies in particular might benefit), but it's also possible that they aided cooling since feather vanes have a blood supply, this could be used to shed some heat by bringing blood up to the surface of the animal.

Written By: Dr Dave Hone
continue to source article at guardian.co.uk

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  1. “what use is half a wing?”

    do creationists actually use that as an argument? there are plenty of modern flightless birds with half a wing or less getting by. of course we know they evolved from flying birds but even if you don’t accept that you’d have to accept a god who carefully designing organs of all animals to do specific things and still knocked up a kakapo.

    in fact if that’s the case, surely asking the question, what us is half a wing, is blashpemy?

    • And we know that birds today with “half a wing” do use them for purposes other than flight, such as shading their eggs, balance, and mating rituals.

      In reply to #1 by SaganTheCat:

      “what use is half a wing?”

      do creationists actually use that as an argument? there are plenty of modern flightless birds with half a wing or less getting by. of course we know they evolved from flying birds but even if you don’t accept that you’d have to accept a god who carefully designing organs…

  2. @OP So then, what might their original function have been, and what prompted them to be maintained, grow larger and change over time? The exact answer is sadly unknown. It is likely a number of factors in concert, or different ones having greater importance over others at various times, and piecing those fragments together is very tricky. However, there are some strong leads and ideas, and for some feather types in some groups the answer is rather convincing.

    To deal with the central issue though, there are in fact various things that feathers may offer animals aside from flight alone.

    Apologies to those who have seem my comments on this on earlier threads.

    Feathers have evolved on a totally unrelated species for purposes such as protection from the sun, protection from the wind, and from sand-blasting by wind driven grit. They also give a measure of protection from predators.

    They have evolved for these purposes on a CACTUS – Mammillaria plumosa.
    http://cactiguide.com/cactus/?genus=Mammillaria&species=plumosa

    Alt Text – (Right click and select “view image”)

    The plumose spines are evolved as branching spines on the Cactus. (Which earlier evolved from leaf stalks.) Some varieties and some related Mammillarias are also rather woolly. The wool provides shade and also collects dew from the air in the arid habitat climates.

    • In reply to #4 by Alan4discussion:

      @OP So then, what might their original function have been, and what prompted them to be maintained, grow larger and change over time? The exact answer is sadly unknown. It is likely a number of factors in concert, or different ones having greater importance over others at various times, and piecing…

      Feathers have evolved on a totally unrelated species for purposes such as protection from the sun, protection from the wind, and from sand-blasting by wind driven grit. They also give a measure of protection from predators.

      They have evolved for these purposes on a CACTUS – Mammillaria plumosa. http://cactiguide.com/cactus/?genus=Mammillaria&species=plumosa

      O.O

      You could have given me a whole month to guess, and I would never have suggested “cactus”.

  3. Surely nothing prompted their evolution. They mutated from skin cells or something, a small bit at a time, and if the modification was useful, it survived, because the animal carrying it had a competitive advantage. If not, bye, bye mutation.

    ‘Tis wise to be careful about language.

  4. I have heard these questions well-answered many times. If creationists ask them, it is not for knowledge but an attempt to embarrass science. They have heard them answered many times. They are looking for a virgin atheist who might be trapped. The word disingenuous was invented to describe such creationists.

    What good is half an eye? There are thousands of species with half-baked eyes for which their eyes give them some advantage. Start with the giant clam. From the point of view of the eagle, humans have only half an eye. It is so inept, the nerves attach to the front of the cornea. What good is half a wing? Ask a flying squirrel.

      • In reply to #11 by Agrajag:

        In reply to #9 by Roedy:

        “From the point of view of the eagle, humans have only half an eye. It is so inept, the nerves attach to the front of the cornea.”

        Retina … :-)

        Steve

        infact all vertebrate eyes have their neurons running on the front side of the retina, so that the light has to pass through that nervous layer (and several other layers of the retina) to reach the rods and cones. So we humans have this ‘feature’ in common with the keen-eyed eagles.

        When I get to discuss the anatomy of the human eye with my students, I usually tell them that I am quite confused why God equipped the summit of his Creation with a worse ocular design than octopuses whose retinal nervous fibers run on the backside of their light-sensing cells. (Needless to say the students’ ability to recognize sarcasm is essential if they want to follow my lessons.)

  5. Some of us kiwis are well aware that feathers often aren’t associated with aviation.

    One application of feathers not mentioned: sensing wind speed and direction.

    Increasingly complex feathers could provide selection pressure, especially for stalking predators, in sensing their prey’s ability to detect the direction of the flow of scent molecules and the relative background noise contribution from air movement from turbulence around leaves in a windy day. i.e. Ears can sense the ambient noise around the stalking animal, but feathers can help remotely infer the ambient noise in the vicinity of the prey.

    A few milliseconds of extra background noise cover for a charging predator could make all the difference in obtaining a meal or not.
    Good hearing and smell, plus very quick reactions and skittishness in response to scent and sound, are the only effective defences available for many grazing animals. So it makes sense that predators would evolve counter-measures.

    • In reply to #10 by Pete H:

      One application of feathers not mentioned: sensing wind speed and direction.

      Increasingly complex feathers could provide selection pressure, especially for stalking predators, in sensing their prey’s ability to detect the direction of the flow of scent molecules and the relative background noise contribution from air movement from turbulence around leaves in a windy day. i.e. Ears can sense the ambient noise around the stalking animal, but feathers can help remotely infer the ambient noise in the vicinity of the prey.

      There is the interesting evolution of comb-like and plumose antennae in insects:-

      Plumose antennae have a brush or feather-like shape. Example: Moths and mosquitoes.

  6. Clearly feathers have more use than flight or flightless birds would have gotten rid of them a long time ago. And even in flightless birds feathery wings have uses – e.g. acting as air brakes for rapid turning or deceleration.

  7. I contend it is like nearly everything in life, it all boils down to sex. Feathers allow the owner a faster biological route to color adornment and pattern changes and thus provide the owner a distinct advantage in female driven sexual selection. Indeed, modern birds clearly show this pattern with males outdoing one another in brighter and louder colors. The use of feathers for flying may well have been an unintended consequence of a drive for color adornment.

    • In reply to #16 by david.winn.900:

      I contend it is like nearly everything in life, it all boils down to sex. Feathers allow the owner a faster biological route to color adornment and pattern changes and thus provide the owner a distinct advantage in female driven sexual selection. Indeed, modern birds clearly show this pattern with m…

      I’d have said mammalian hair would have served a display purpose just as well as feathers, but without the intricate barbs and vanes to complicate the design. Given that feathers started simply as hollow strands, this might have been the original purpose, but I think a more survival-oriented function would have been more important. Feathers can provide a good, strong flying structure while also being able to withstand and recover more damage than skin-flaps or fur, so I think the need for aerodynamic design played the main role in feather evolution, and display and insulation provided side-bonuses.

      • In reply to #17 by Zeuglodon:

        I think the need for aerodynamic design played the main role in feather evolution, and display and insulation provided side-bonuses.

        I think aerodynamic design would only be relevant to the later stages flight feathers in birds. Some dinosaurs had feathers for millions of years without ever developing flight.

        • In reply to #18 by Alan4discussion:

          In reply to #17 by Zeuglodon:

          I think the need for aerodynamic design played the main role in feather evolution, and display and insulation provided side-bonuses.

          I think aerodynamic design would only be relevant to the later stages flight feathers in birds. Some dinosaurs had feathers for millio…

          I did acknowledge that the initial selection pressure could have been for insulation, but I’m trying to think why that would entail the evolution of a complex feather design rather than a more straightforward alternative of mammalian fur. At present, I think the barbed design is most likely to have come about when the initial insulating feathers were recruited for aerodynamic purposes. This could be tested by checking if the complexity of the feather design occurs alongside dinosaurs capable of flight or gliding.

          • In reply to #22 by Zeuglodon:

            At present, I think the barbed design is most likely to have come about when the initial insulating feathers were recruited for aerodynamic purposes. This could be tested by checking if the complexity of the feather design occurs alongside dinosaurs capable of flight or gliding.

            Given the millions of years of feather evolution pre-flight, there are many issues re. the complexities of feather structures. One interesting feature is that we can infer the colours on some dinosaur feathers from fossils, because the colouration is derived from diffraction patterns rather than pigments (which would have degraded over time).

            http://www.electron.rmutphysics.com/physics/charud/scibook/Physics-for-Scientists-and-Engineers-Serway-Beichne%206edr-4/37%20-%20Interference%20of%20Light%20Waves.pdf
            The colors in many of a hummingbird’s feathers are not due to pigment.
            The iridescence that makes the brilliant colors that often appear on the throat and belly is due to an interference effect caused by structures in the feathers.
            The colors will vary with the viewing angle.

            Display and camouflage would be obvious benefits of colouration.

  8. Look at a picture of a bird. Notice how it is covered in feathers over its whole body except its feet. Only a fraction of them are used for flight. Look of a picture of a bird in winter. They fluff their feathers up. There, it is obvious the primary function of feathers is warmth.

    • In reply to #20 by Roedy:

      Look of a picture of a bird in winter. They fluff their feathers up. There, it is obvious the primary function of feathers is warmth.

      Except on the Cactus @4, they keep the heat out!

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