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Re: CNN on Lungs and Feathers



GSPaul wrote:

>Regarding the discussion concerning the meaning of the presence of pneumatic
>verterbrae and other skeletal adaptations in theropods. 
>
>The importance of pneumatic vertebrae is that they essentially prove the
>presence of air-sacs in theropods. This is according to Britt (in the
>Encylopedia of Dinosaurs) and Reid (BYU Geol. Studies 1996). 

And also in pterosaurs, sauropods and snakes.  

>The next question is whether theropods had the skeletal adaptations needed to
>ventilate more ventral and posterior air-sacs. It is important to understand
>that many avian adaptations are not critical to this system. Large ossified
>sternal plates, ossified uncinate processes, and broad ribs are all absent in
>various birds, especially nonflying forms. At the same time dromaeosaurs had
>large sternal plates and ossified uncinate processes. So go figure. Anyway,
>what IS needed are long posterior ribs with well developed double heads that
>allow them to be highly mobile. These can change the volume of posterior
>air-sacs, and they most certainly are present in theropods, especially
>avetheropods which have the most bird-like trunks of any tetrapods. Because
>theropods had both pneumatic bones, and ribs able to operate air-sacs, they
>had a preavian respiraotry complex. 

As I understand it, birds have two methods of pumping the caudal air sacs.
First, the "normal" flying method which involves depression of the sternal
plate.  This is not availible to theropods because they generally lack the
equipment.  The alternative, "perching" method requires depression of the
pelvis and is usually managed by means of a severe retroversion of the pubes
so that the are pointing posteriorly.  Although theropod pubes tend to be
less antero-ventral than crocs, they don't approach the orientation seen in
modern birds or Archaeopteryx.

You have suggested elsewhere that Theropod caudal airsacs could have been
powered by rib compression.  I don't see anything wrong with this idea at
all (though what would I know?); however, it isn't the same as either of the
avian systems.

>Back to birds, there have been arguments that enantiornithines had rather low
>metabolic rates, in part because they lacked ossified sternal ribs that may
>be needed to achieve the high aerobic exercise capacity of flying birds. Yet
>Late Cretaceous Neuquenornis had ossified sternal ribs and a sternum as large
>as in modern birds. Looks like the fossil bird's aerobic flight capacity was
>as high as in living examples. 

Pterosaurs managed it without endothermy.  Bats manage it with endothermy
but without air sacs.  Snakes and some lizards have the air sacs but no
endothermy.  The hepatic pump hypothesis presents a very important
evolutionary puzzle, but I doubt that the endothermy part of it has much to
do with resolving the BADD debate.

>As for croc-lungs in dinosaurs, Phil Currie has just returned from examining
>the type Sinosauropteryx slab. And no Virginia, Ruben et al's septum does not
>exist, it's complete air from top to bottom. So much for that notion. 

This all looks pretty subjective.  I'd be a lot more comfortable if he'd
taken someone from Ruben's lab with him.

  --Toby White