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Re: If Dinosaurs Could Fly



>I think you're missing the point.  Not all feathers serve an insulatory
>function.  In modern birds insulatory feathers are down feathers, not
>flight/contour feathers.  Down feathers are highly derived feathers.
 

This is not to say, though, that contour feathers can have no insulating
function.  More to the point, it says nothing about the insulating
properties of "protofeathers", if that is what the structures on
Sinosauropteryx really are.  And it avoids other possible uses of body
feathers such as display.

>  The
>feathers from which down feathers are derived functioned in flight, not
>insulation. 

There is simply no hard evidence of which I am aware to support this
statement.  Frankly, we do not know whether contour and down feathers (as
well as bristles, filoplumes and other feather types) evolved from flight
feathers, or all of these evolved from an ancestral type (which might have
been the Sinosauropteryx-type protofeather).  

This is part of the evidence that (in birds) powered flight
>evolved well before endothermy.  

As this is a conclusion, not a description of actual findings, it is not
"evidence" of anything.  As we do not know of a single fossil bird or bird
ancestor capable of flight but unambiguously lacking body feathers, any
conclusions about endothermy in early birds must come from other evidence
such as RT's (and this evidence seems to be pretty equivocal too).  The
fact seems to be that we just don't know which came first, or when and how
each evolved (hence all the debate, of course).

There is a logical evolutionary progression
>from scales (in ectothemic avian ancestors) to flight/contour feathers (in
>ectothermic early birds) and finally to downy feathers (in later, enothermic
>[ornithurine] birds). 

I know of no evidence on the appearance of down; for all we know
Archeopteryx could have been buried in the stuff, but it just didn't
fossilize.  There may be a speculative evolutionary progression, but when
it comes to the facts we come up pretty short.  In fact I do not thik the
progression you propose is "logical" at all - it seems supremely illogical,
evolutionarily and/or developmentally speaking, to assume that a highly
specialized integumentary structure would develop to a considerable degree
of refinement on one part of the body and then (and only then) be modified
for a different function on other parts of the body.  If Currie is right
about his interpretation of Protoarchaeopteryx, the evidence is that more
than one type of featherlike structure could be present simultaneously on
even a creature well down on the bird family tree (whether or not its
features correspond to those on Archaeopteryx's true ancestor, whatever
that was).

It wouldn't surprise me that once the evolution of filamentous structures
took place in birds or their ancestors, specializations for different
functions were selected for simultaneously on structures on different parts
of the body (including not just insulation and flight feathers but display
feathers, tactile feathers such as bristles, eyelashes, perhaps even such
highly specialized things as powder-down feathers.  To my knowledge we have
no hard evidence of when these structures appeared, or in what order.

 In order to have insulatory feathers in the earliest
>birds they would have to appear intact out of the blue!!!

Why?  Just because down is a remarkably fine insulator does not mean that a
less "downy" precursor might not have provided slightly better insulation
than, say, scales or bare skin, and thus conferred a relative advantage on
their possessor.
--
Ronald I. Orenstein                           Phone: (905) 820-7886
International Wildlife Coalition              Fax/Modem: (905) 569-0116
1825 Shady Creek Court                 
Mississauga, Ontario, Canada L5L 3W2          mailto:ornstn@inforamp.net