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Re: Air sacs in extant non-avian reptiles?



Eric Lurio wrote...
>The people here tend to forget why the linnean system worked so well in the
>first place. The classes were soooooo different from each other that had to
>be seperated.[snip]


    A hundred years a ago the lines were a little eaier to draw then they
are today because we know more forms that blur the lines between the
classes.  For example, based on morphology, where would you put the line
between birds and reptiles?  At Archaeopteryx because it was feathered and
was warm-blooded?  An easy distinction forty years ago, but nowadays we
aren't so sure were that line is drawn.  Dromeosaurs were likely feathered,
and possibly warm-blooded as well, and thier morphology in general matches
Archaeopteryx very well.  If Greg Paul and George Olshevsky are right about
secondary flightlesness in coelurosaurs, even flight is not a solid criteria
for seperating them. Obviously, we can identify features to distinguish
Archaeopteryx and birds from dinosaurs or we wouldn't be able to diagnose
Aves, but what is so special about THOSE characteristics that they warrent
distinguishing two major classes?  Chiappe's chapter on Aves in Encyclopedia
of Dinosaurs gives: "Unserrated teeth with constriction between crown and
bases, tail short (less then 25-26 elements) with short prezygapophyses,
fully retroverted hallux".  Which of these characters do you want to be THE
defining character seperating classes? (As Tom Holtze would mention, there
is evidence that the unserrrated, constricted teeth are present in juvenile
dromeosaurs anyway).

>Okay, can you tell me ONE professional ornthologist who belives that birds
>are currently reptiles? Not aknowleging the possibility of dinosaur
ancestry,
>but currently having the same characteristics as lizards, snakes and
turtles.

    WHICH of the same charateristics?  Birds are feathered and endothermic,
but birds share other features in common with living reptiles, which is the
reason cladistic analysis put them in Reptilia (non-vernacular) in the first
place.  I don't think any ornithologist would deny that birds and reptiles
have features in common.  No paleontologist that I know of thinks that
lizards, snakes and turtles are feathered endotherms either.

LN Jeff

Be silent always when you doubt your sense.
-Alexander Pope

Read the best books first, or you may not have the chance to read them at
all.
-Henry David Thoreau

Jeffrey W. Martz
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