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Re: New Refs #4



At 09:39 AM 12/10/97 -0500, Ralph Chapman wrote:
>
>Ruben, J.A., T.D. Jones, N.R. Geist & W.J. Hillenius. 1997. Lung
>   structure and ventilation in theropod dinosaurs and early birds.
>   Science 278:1267-1270. 14November97

I finally got around to reading this.

I found it quite interesting, even if less than convincing.

One aspect I do not think they really nail down well enough is the
anatomical correlates of air-sac based respiration.  IMHO, just because
birds rely on a particular mechanism for ventilating the air-sacs does not
mean that is the *only* possible mechanism.  it is quite possible that,
once the modern avian mechanism evolved, birds *lost* the older one.

On a related note, it almost sounds as if they consider the *abdominal*
air-sacs as primary, and the thoracic ones as later.  Given that vertebral
pneumaticity in dinosaurs shows up first in cervicals and anterior dorsals,
it looks to me more as if thoracic air-sacs developed first, and then the
abdominal.  This pretty much obviates the "hernia" problem with the
diaphragm, as that need not happen until *after* the air-sac based system
evolved.

--------------
May the peace of God be with you.         sarima@ix.netcom.com
                                          sfriesen@netlock.com