[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: If Dinosaurs Could Fly



>Modern birds--which are unarguably feathered-- are able to take up and give
>off heat in regions of the body lacking down (e.g., the back).  If contour
>feathers had a significant insulatory function this would not be the case
>(and we would make coats and sleeping bags from contour feathers not down).
>Down feathers work as insulation because of the air they are able to trap.

This is not quite accurate.  While sunning, birds usually elevate their
contour feathers to expose bare skin to the sun - something that would
hardly be necessary if contour feathers provided no insulation.  The same
is true of the brood patch, a featherless area on the abdomen of female
birds that develops during the nesting cycle.  Some birds (eg roadrunners,
grebes) have special areas of black-based feathers or pigmented skin that
assist in heat uptake.

>>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 from the embryological evidence.

I'd be curious to see this.  According to the article "Feather" in "a
Dictionary of Birds" (British Ornithologists' Union 1985, the section on
development of feathers leads into the statement that the contour feather
"is... probably the fundamental type".

>
>There is significant evidence for the origin of avian flight occuring before
>the origin of avian endothermy.  See papers by Randolph; Ruben; Chinsamy
>that I've mentioned before.

There are certainly claims to that effect, but they do not seem to be
universally accepted.  I have not read these papers, I must admit, but it
seems to me that all that they show is that certain features that MAY be
correlates of endothermy are absent in early birds.  This may be
suggestive, but it is hardly conclusive (nor does it allow for intermediate
stages between full endothermy and ectothermy; in fact the presence of
less-than-perfect insulating structures could be related to just such an
intermediate stage.  Anyway, the evidence is still not that Archaeopteryx
was an endotherm; that is a conclusion.  The evidence is that it lacks
RT's, etc.

>There is no evidence of down feathers on any pre-ornithurine animal.
>Admittedly, this is negative evidence, but combined with the other evidence
>we have it seems we currently have but one logical conlusion...

Why? How many ornithurine fossils have down?  It seems to me that the
"logical conclusion" is that down fossilizes poorly.
--
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