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Dino-lung ventilation



 
 I was reading_ Ruben et. al._'s  ariticle on dinosaur physiology in _ 
The Complete Dinosaur_ a few days ago and I came across a curious 
statement. They claimed that Deinonychus and presumably all 
dromaeosaurids had a short, immobile sternum. They concluded from that 
statement that dromaeosaurids did not have high breathing rates. 
Actually dromaeosaurids ( and most Maniraptorans and Maniraptorformes ) 
have quite big and bird-like sternae. The dromaeosaurid sternum is 
posteriorly expanded and widened laterally. It is quite bird-like in 
appearance and appears ( to me at least ) to be developing a carinate. 
Ruben et. al. correctly point out that a posteriorly expanded sternum 
helps maintain high tachymetabolic breathing rates because it is able to 
move ventrally during inhalation and cranially during exhalation. They 
also cite that lengthened ribs also help the lung maintain high 
breathing rates. Dromaeosaurids ( contra Ruben et.al. ) also have 
lengthened ribs. 
 Interestingly in dromaeosaurids they possess, just like Ornithurae 
birds, uncinates on the ribs. They are clearly visible on the " fighting 
" Velociraptor and Greg Paul points out that some isolated bones may 
also be uncinates in the Deinonychus assemblage. Uncinates bind the 
rib-cage to stiffen it during flight. They also, as Feduccia and Ruben 
point out, ventilate the abdominal air-sac region in birds ( along with 
the expanded sternum.) This shows that at least dromaeosaurids had high 
breathing rates resembling tachymetabolic endotherms and a fairly modern 
air-sac system. 
 We can expand these observations to all dinosaurs now. All dinosaurs 
that have been found with intact sternae have relatively elongated 
sternae ( Iguanadon and Sinraptor for example.) And all dinosaurs ( Paul 
1988 ; PDW ) have long ribs. Avetheropods probably had high breathing 
rates because they all have furculae. Furculae have been shown to have a 
possible role in high tachymetabolic breathing rates in birds. Nasal 
turbinates are the only thing that are missing in dinosaurs that are 
associated with high breathing rates.   (But have I heard correctly or 
did "Stan" have nasal turbinates? Then again they could have been 
olfactory turbinates.) 
 I have not read the recent article concerning the non-homology of 
dinosaur-bird lungs, so I cannot give a good scientific opinion on that 
issue, bu in light of the evidence above I have my doubts. But one thing 
can be certain dinosaurs probably did have high breathing rates.

 WMattTroutman 

 
 

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