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Re: Lungs and Feathers



Alas, White continues to make assertions that are incorrect. He posted a list
of specific skeletal attributes indicative of a preavian air-sac complex that
he believes Sinosauropteryx lacks. Sinosauropteryx is a typical, basal
avetheropod, and did have the appropriate thoraxic adaptations. As can be
seen in the photographes, the mid-dorsal ribs ARE shorter than the chest
ribs. This is like birds, but unlike more basal theropods whose chest ribs
are every bit as long as those more posterior, which is the typical tetrapod
condition retained by crocs. The short chest ribs indicate that the lungs of
Sino. were no longer large and flexible as per most tetrapods and crocs, but
were rather reduced and rigid as in birds. An authority on tetrapod lungs has
told be that the rib heads of theropods also indicate that the lungs were
dorsally expanded in the avian manner. There is absolutely no croc-like
lumber region in Sinosauropteryx - the moderatel
y protracted femur overlaps the posterior ribs - and the latter are more
elongated than those of most other archosaurs. The posterior ribs heads are
also double headed and mobile. Both are avian adaptations that allowed the
posterior ribs to ventilate moderately developed posterior air-sacs. The
manner in which intercostal muscles operate these ribs has been described by
Duncker (1971), Fedde (1987) and others. It cannot be overemphasized that
kiwis simply do not have sternal plates long enough to operate the posterior
air-sacs, only the ribs can operate them. White admits he is not familiar
with the extensive new data that show that the pubis of Archaeopteryx was
less retroverted than those of some theropods, and hardly more than in
Sinosauropteryx. Pubis orientation is extremely variable among theropods
(goes from nil to extreme within dromaeosaurs and alvarezsaurs respectively)
and birds (from nil in Archaeopteryx to extreme in most birds), so it is not
tightly linked with respiration.  

White keeps making the mistake - made by so many others - of focusing on
modern flying birds as the sole model for understanding air-sac function. Of
course, flightless birds are much better models for restoring the pre-avian
respiratory complexes of dinosaurs. As for Sinosauropteryx, with superficial
insulation, an early air-sac complex, and long erect legs powering walking
speeds well above those sustainable by reptiles with simple, dead end lungs,
that little sucker very probably was a tachymetabolic/aerobic endotherm. Was
its air-sac complex large and well developed enough to sustain powered
flight? Of course not. Nor are those of kiwis.   

Am I suggesting sauropods had a bird-like air-sac complex? You bet, and so
have others. Of course the intensely pneumatic vertebrae confirm the presence
of air-sacs. The ribcage, especially the rib-head/vertebral articulations, is
remarkably bird-like. The long mobile abdominal ribs could ventilate the
posterior air-sacs. This very efficient respiratory system probably evolved
in order to overcome the dead space inherent to their very long trachea. 

As for pterosaur energetics, it was White who stated that pterosaurs were not
endotherms, he did not say they might be one or the other. Ectothermy in
pterosaurs is an unsubsantiated minority view. The great majority of workers
continue to agree that pterosaurs clearly paralleled birds in being
tachyaerobic, insulated, flying endotherms with some form of air-sac
ventilated lungs.  

GSPaul