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Re: Bristles before down: A new perspective on the functional origin of feathers



dale mcinnes <wdm1949@hotmail.com> wrote:

> Let me take this a big step forward. I really like the idea of
> thermoregulating "wicks" for transferring heat away from the body. But let's
> continue in that vane [no pun intended]. Why wouldn't a full pelt of
> feathers continue beyond bristles, to take heat from the body ?


I can only refer you to how Myhrvold &c address this question
regarding hair: "At low densities, hair has almost no effect on air
flow and does not trap an insulating air layer near the skin, but the
extended hair acts as a pin fin that increases thermal exchanges with
the surrounding air. Thus, as the hair density decreases from that of
very furry animals, a break-even point is reached where the hair
function switches from an insulator to a heat exchanger."


I don't know if the same principle would apply to bristle-like and/or
filamentous feathers.


> Back in the early triassic, mammals burrowed
> to get rid of heat. Early archosaurs stayed outside. Mammals remained small.
> Archosaurs were uninhibited in increasing their size [didn't have to
> burrow]. My 2 cents.


I don't think I can speculate sensibly on this (or on the part of your
message that I snipped).  It is worth noting that certain small
ornithischians did burrow, such as the orodromine thescelosaurids
(e.g., _Oryctodromeus_) and maybe others, such as the enigmatic
_Drinker_.





Cheers

Tim