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Re: the Horner interview - "fluffy" T. Rex??



Hammer <hammeris1@att.net> wrote:

> I thought the general consensus was that LARGE adult tyrannosaurs like 
> Albertosaurus would not have feathers (except a possibly a few on the arms or 
> top of the head) due to the problem
> of shedding excess heat in these many-times-the-size-of-a-raptor type animals?


I know this doesn't directly answer your question... but in large
mammals it has been suggested that a sparse distribution of hair
actually helps to *shed* excess body heat.  This hypothesis was
proposed in a fairly recent study of elephant hair (Myhrvold et al.,
2012; doi:10.1371/journal.pone.0047018.).  At low densities, hair
apparently does not trap an insulating air layer near the skin;
instead, each extended hair acts as a 'wick' to shed heat into the
surrounding air.  (This principle was then used to propose that the
first hairs were used by mammal ancestors living in warm climates to
shed heat, and were later exapted for insulation via increased density
of these hairs.)

A heat-shedding function might also have been true of the epidermal
structures of large theropods.  In this case, bristle-like epidermal
structures ('proto-feathers') sparsely distributed over the body could
have helped rid the animal of surplus heat.



Ruben Safir <ruben@mrbrklyn.com> wrote:

> Show an example where a bird loses feather.  Show a model where feathers 
> retain heat for a tropical bird?  Feathers are not hair.


True, feathers are not hair.  Nevertheless, down feathers and thick
hair both play roles in heat conservation, by trapping warm air.

Many tropical birds lack down feathers, at least as adults.  Their
feathers are used for flight and display.  When hot, erection of the
contour feathers exposes the bare skin, which allows body heat to be
lost.

I believe ostriches mostly lack down feathers, although there is a
thin layer of down along the neck.







Cheers
Tim