Vivian on 12/12/2016 at 08:09

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Nah man, how would covering yourself in a fluffy, air-trapping layer act as cooling? You ever worn a down-stuffed coat? Seriously, these proto-feather structures are insulation. Once you get the tertiary barbule things that let them form smooth sheets (like on the contour feathers of flying birds) the juries still out as to whether it was initially a display thing or whether it was waterproofing (I'd go with the latter, contour feather structure fits the requirements of breathable waterproofing almost perfectly), but the downy layer like you see in this fossil? Insulation, unambiguously. Don't forget you still have cold evenings and mornings etc even if Jurassic temperature was warmer than the average now. And most early coelurosaurs were small, so they'd lose heat to the environment fast, which is really bad if you're an endotherm.

Pyrian on 12/12/2016 at 18:26

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By pumping a warm liquid through it to act as a radiator. Feathers are too complicated to grow as "dead" keratin from a single follicle like hairs do; growing feathers (known as "pin feathers" or "blood feathers") actually require a blood supply. Now, given that insulating feathers require a radiating stage before they can become insulating, whereas radiating feathers do not require an insulating stage at all, it is not unreasonable to guess that the very earliest "feather" ancestors might very well have originally functioned to radiate heat rather than to insulate.

Tocky on 13/12/2016 at 02:34

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Not necessarily. Birds fluff their feathers (make them stand out) often, particularly when preening or fighting. The goose bump effect could actually funnel air beneath and if moved back and forth work as a fan. Blood does indeed fill the long claws of finch feet so why not quill? I figure they survived and were successful for some of the same reasons we were and heat dispersal on the chase was damned important whether you were chaser or chasee. Endothermic depends on not overheating and damn near everything wanted to eat you.

I think feathers could do all the things mentioned from shedding water which would cool too much to insulating when drawn flat and back to cooling whether with flapping of arms as chickens do or making them stand out and accept air flow. BUT what the devil was this tree branching feather thing for? That would seem to indicate drooping weight as for cold weather protection. Was there a temperature change at some point? When the earth cooled after the asteroid did they attempt adaption? Were there fluctuations as with the ice age then? This branching thing is a puzzle.

Vivian on 13/12/2016 at 10:04

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The branching structure traps air for insulation. It's seriously not that mysterious. And the hunting/chasing thing, these were small, flighty and most likely insectivorous things we're talking about, not wolf analogues. Large-ish pursuit predators are not the first things you see with feathers, and seriously, raising feathers up like hot birds do is not more efficient at cooling than just not having feathers. Look at the major endothermic animals we've got today. Notice any constant, furry features? Is there anything alive that uses a fluffy skin covering to cool down?

Feathers as cooling a) doesn't fit with how they're currently used, so you'd need novel evidence to support it as a hypothesis anyway, b) doesn't fit with what equivalent skin covering in mammals does, and c) doesn't scale like you would expect a cooling adapation to, bigger theropods (which would get hotter just due to mass vs surface area scaling) do not have more covering of feathers.

The cooling adapations that might make more sense for what you're talking about, sustained locomotion etc, are more likely to be linked to the lungs. Theropods also developed a massive network of air sacs that helped ventilate their lungs (bird lungs are super wierd), which would definitely give them a highly vascularised, high-surface-area organ with good air throughout for heat exchange.

Dema, latest work on KT impact event survival points at beaks and granivory probably being significant, there was a link in the other thread, hand on...
Here you go, it's not open access unfortunately: (http://www.cell.com/current-biology/abstract/S0960-9822(16)30253-6)
I can dig out a copy when I'm in the office next.

Pyrian on 13/12/2016 at 18:33

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You are seriously hung up on the "fluffy" thing, when the whole point of examining the evolutionary pathway is precisely the fact that you need a blooded quill to get a fluffy feather, but do not need a fluffy feather to have a blooded quill. I'm not suggesting the proto-feather was a "fluffy radiator" on a small animal. I'm suggesting it started as a bare radiating quill on a large animal, then developed a fanning capability to aid in radiating heat. Later it would diversify into insulation, and eventually back into an air-moving structure.

I mean, look at that amber sample. The bristles are closely aligned. Down is only like that at the top; fur isn't normally like that at all. It looks like it's evolving to insulation rather than from it.

Here's a modern example of a large animal with a blooded, radiating, fanning structure used for cooling down:

http://i32.photobucket.com/albums/d3/Pyrian/800px-African_Bush_Elephant_zps5kdoip9i.jpg

Bird lungs are fascinating, but it's a lot easier to see how they could have evolved from the need to supply a great deal of oxygen to a very large body, than to see how they could have evolved from a heat-dispersal capacity. The cross-current is more suited to heat retention. From a thermodynamics perspective, a captive air supply just isn't a good place to try to radiate even more heat into.