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Re: Lungs and Feathers (fwd)



Terry Jones recently wrote of Leon Claessens' work, and Leon noticed
it in the archives.  I've instructed listproc to accept his mail even
though he's not subscribed to the list, but I was thwarted by the fact
that the address in his signature is slightly different from the one
listproc extracted from the header of his message.  This was his
second attempt to get this message to the list; I'm forwarding it on
his behalf rather than asking him to try again... in the future he may
write to the list directly, but don't expect him to see any responses
you send to the list now or then; if you want him to read a response
make sure you send him a direct copy.

--
Mickey Rowe     (mrowe@indiana.edu)

-------- beginning of forwarded message -- MPR
From: Leon Claessens <lclaesse@oeb.harvard.edu>
Reply-To: Leon Claessens <lclaesse@oeb.harvard.edu>
To: dinosaur@usc.edu
Subject: Re: Lungs and Feathers (fwd)

The mailing list's discussion on dinosaur / theropod lung ventilation is
very interesting, and shows that the subject is still under active
investigation. Greg Paul brings up many valid osteological and
sedimentological objections against the hepatic piston pump model of
Ruben, Jones, Geist and Hillenius. However, the importance of the
physiological aspect in these inquiries should not be underestimated. I'll
just briefly comment on the possible involvement of the gastralia in this
matter. Please note that I am not a regular subscriber to the mailing
list, and only occasionally follow it's proceedings. 

--
On Mon, Jan 12 1998, Terry D. Jones wrote:

> Furthermore, it is unclear as to the mobility of the gastralia (I
> assume that Leon Claessens is still looking at this question).
> Regardless, it is doubtful that movements of the gastralia would
> result in significant changes in intraabominal pressure to allow
> filling and/or emptying of abdominal air sacs.

--

I would state that, considering the morphology of the gastralia in
theropods, it is undoubtedly a kinetic system. What the function of this
system was, is the appropriate question. I'd consider any passive
function, like viscera support or stomach-size-adjustment, to be secondary
an active function.  Here only respiration is a valid contender (I've even
considered functions as wild as external manipulation of the stomach). 

The gastralia could have been an external diaphragm analogue, but
volume-wise possibly not too effective. If lung diverticularization, or
differentiation of the caudal sac-like lung region into an abdominal
air-sac had occured, the kinetic gastralia would have been well suited for
operating them. Exact volume differences generated by gastralia movement
need further calculation, especially because they can not be considered
independantly of whole trunk dynamics. These studies are underway.

Off course, Steven Perry suggested a long time ago the that gastralia
would also prevent paradoxical inward movement of the viscera upon
inspiration.

I agree with Terry Jones that caution is needed when using terminology
concerning lung diverticularization and pneumaticity. Lung diverticula are
not necessarily air-sacs as observed in various states of development in
extant birds. Air-sacs or lung diverticula do not necessarily imply
uni-directional airflow. Archaeopteryx did not necessarily have
uni-directional airflow because it was a bird. On the other hand,
theropods like Dromaeosaurus did not necessarily not have such a system.
As a matter of fact, the prerequisites for cross-current gas exchange are
already present in the crocodilian lung. The many morphological
similarities between advanced theropods and birds argue for the
development of bird like lungs (relatively late) in the Theropoda-Aves
lineage.

Also, I am not quite sure that Greg Paul is referring to gastralia when
speaking of abdominal ribs in sauropod lung ventilation. The term
abdominal ribs is not preferred, due to its use for various different
structures in the abdominal skeleton over the century. It is probably also
no secret that I claim that sauropods do not have gastralia, and that the
Apatosaurus yahnapin and other bone structures represent mis-identified
sternal and xiphisternal elements. My paper on gastralia morphology and
function is, after more than a year of shelf-life, finally ready to be
submitted.

As a final statement, I noticed that Greg Paul, Terry Jones et al., and
Rich Hengst are giving presentations on dinosaur respiration at dinofest
in April.  Steve Perry, Phil Currie and I will also give a talk on the
subject. All of this promises some interesting exchange of opinions and
ideas. 

Leon

--- 
Leon Claessens                                  tel. 617-493-4177
Museum of Comparative Zoology                   fax. 617-495-5667
Harvard University                              lclaessens@oeb.harvard.edu
26 Oxford Street
Cambridge, MA 02138
USA