RE: Air sacs in extant non-avian reptiles?

["Henri Rönkkö" <overmind@iobox.fi>]

I thank you for your reply, but I'm afraid there was a misunderstanding. I was 
talking about extant, in other words, modern, nowdays reptiles (non-avian 
ones). I have read that some of the both non-dinosaurian and non-avian reptiles 
that live among us today have air sacs attached to their lungs. The sources of 
mine are David Norman's book "Prehistoric life" and GSP's message to the DML; 
the latter critisized the theropod lung articles of Ruben's team.

Now, I am pretty confident that the claims conserning the presence of pulmonary 
air-sacs in some of today's non-avian and non-dinosaurian reptiles is based on 
some real evidence. I would like to know the names of the animals.

And as we all know, air circulates unidirectionally in the avian pulmonary 
complex. Today's non-avian and non-dinosaurian reptiles, as well as mammals, in 
turn, have inefficient "dead-end" lungs. I was wondering, what possible use 
could today's non-avian and non-dinosaurian reptiles possessing pulmonary air 
sacs have for these air sacs, and asking anyone possessing the information to 
reply me.

Previous discussion:

> > I have read that ait sacs extending from the lungs are present in some
> > extant, non-avian reptiles. I'd be interested to know the names of these
> > reptiles. Also, if someone has tried to explain the function of these
> > structures in these dead-end lungs, please tell me.
> >
> > Best wishes,
> >
> > Henri Rönkkö >>

- discussion on taxonomy snipped -

> There are various types of air sacs in birds (some in the skull, some in the
> body).  With your reference to the lungs, you are referring to the ones in
> the body.
> 
> The actual soft tissue of the air sacs have only been described so far in
> modern birds. Indeed, we don't have them preserved in fossil birds of the
> Mesozoic or Cenozoic, but their presence of some of them can be inferred by
> complex cavities in the bone.  Chambers of the same morphology are found in
> almost every advanced theropod dinosaur: dromaeosaurs, troodontids,
> oviraptorosaurs, therizinosauroids, tyrannosaurids, ornithomimosaurs, and
> carnosaurs.  Less complex chambers are found in ceratosaurian theropods and
> sauropod dinosaurs.  Pterosaurs have similar chambers in their vertebrae.
> 
> Air sac tissue itself is not yet described for these fossils: only the bone
> is found.  However, the presence of the airsacs is inferred for these
> animals in the same way it is inferred for _Archaeopteryx_ or _Ichthyornis_
> or other animals which are considered "birds" but which lie outside the
> group comprised of all living birds (the only animals for which we can
> definitely point to the sacs).  The histology of the bone surround these
> chambers is identical to those seem in the pneumatic bones of birds.
> 
> As for the purpose of these air sacs: by shunting air from trachea to lungs
> to air sacs and out again, there is a one-way (rather than two-way) flow of
> air into the lungs.
> 
> P.S.  Although the position of birds as maniraptoran coleurosaurian theropod
> saurischian dinosaurs lends support to the hypothesis that the chambered
> vertebrae of saurischians were related to air sacs, some of the great old
> traditional paleontologists, such as Swinton and Romer and Janensch (who did
> not accept a dinosaurian origin of birds) also supported the idea of an
> avian air sac system in Saurischia.

- snip -
----
Soittoäänet ja ikonit matkapuhelimeen!  http://www.iobox.fi/