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Re: Dino Feathers



At 11:57 PM 7/30/95, DPterosaur@aol.com wrote:
>Has anyone ever considered the use of feathers on Archaeopteryx and previous
>birds for basking?  By that I mean I have seen any number of small and large
>birds extending their wings so as to catch the maximum amount of
>sunlight--and on some of the hottest days of summer! They certainly have no
>need to bask, but it looks as though they are very content while at it.  (I
>am aware of the aerodynamic morphology of Archaeo. feathers, so please no
>letters on that.)

        To take your second point first, I think it more likely, as Neil
said, that the birds you witnessed performing thus were probably _cooling_
more than they were heating -- it's very easy to overheat a small animal
(as anyone who's kept a mouse in a tiny container for a short period of
time can attest!), and with a blazing summer sun, I think it unlikely that
a bird would be trying to warm up!

        But anyway...it's ~sort of ~ been proposed that the feathers were
used for "basking," although basking is a term I personally tend to
associate with reptiles (human sun bathers notwithstanding) as a means of
ectothermically obtaining energy and warmth.  I forget just who at the
moment, but someone in _The Beginnings of Birds_ proposed that
_Archaeopteryx_ used the feathers to shade areas beneath the wings whils
wading as a means of attracting and spotting fish for food.  I don't think
anyone ever bought that one.  8-)

        The bigger question would be:  why would a bird bask?  As I
mentioned, basking is something that ectotherms must do, but endotherms do
not (except for comfort, apparently).  For _Archaeopteryx_ to be basking,
you're basically saying that it's probably an ectotherm.  And while yes, I
know that some recent research points to Mesozoic birds not having
identical metabolic rates as modern birds do, I still think it more
parsimonious to think small theropodomorphs, including _Archaeopteryx_,
were more than ectotherms.  In reverse, if _Archaeopteryx_ was using the
feathers for cooling...well, let's just say then that it would've been
better off _without_ the feathers for rapid cooling!  So I don't think that
the feathers had a cooling effect, and I'm not convinced that they were
insulatory, either (although feathers as a whole may have evolved that
way).

>It is very clear by the morphology of the manus that Archaeopteryx, like
>pterosaurs, was very good at hanging on tree trunks, the best places to catch
>rays early in the day.  The modern frillneck lizards do likewise (and they
>walk bipedally too!.  I know that feathers have no arterial connection, but
>once warmed up and placed against naked skin, it must be like having a hot
>blanket layed on.  This analogy is particularly apt in the case of pterosaurs
>in which the wing (or pre-wing) membrane can be extended without shifting the
>clinging digits.

        Oooooooh, you're sure to spark a debate between the "trees down"
flight origins theorists and the "ground up" faction!  ;-)

>Speaking of the morphology of the manus, can anyone report either a bird or a
>dromaeosaur in which the fingers are preserved curled (flexed)?  I have never
>seen a specimen that was not fully extended (but I don't have great access,
>either).  Could it be that these dinosaurs had "stiff" fingers?

        What would be the point?  Why would the maniraptorans (think of the
origin of that name...) evolve long fingers with, as Tom Holtz pointed out,
wonderfully developed articular surfaces just to keep the fingers rigid?
No, it makes more sense to think that such highly developed traits were
used for something, and grabbing and/or swiping are probably big parts of
it.

        While we're on the subject, and now that the famed Greg Paul is in
our midst (Hi Greg!), what does everyone think about the now-common
pictures of theropods (etc.) running with the arms all tucked up?  It does
look kind of cool, but do you think it really happened?  I'm certain that
for aerodynamic reasons, they kept the arms close in to their _sides_, but
I'm not so sure about having them all curled up (a la bird wings)...



Jerry D. Harris
Schuler Museum of Paleontology
Southern Methodist University
jdharris@lust.isem.smu.edu
        (Compuserve:  73132,3372)

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