SVP DINORESPIRATION

[GSP1954@aol.com]

A few minor corrections concerning my fast paced talk in Pete's epic summary
of the fascinating dinotalks at SVP. Plus, some additions to my presentation.

I did not use phylogenetic bracketing to restore basal gracile crocodilians
with a liver-piston lung system, PB is inappropriate to use in this case
because the ancestoral condition was proabably the normal reptilian system.
What I did was show that basal crocs had some but not all of the skeletal
respiratory adapations seen in their descendents, which suggests the unusual
crocodilian respiratory complex was in the process of evolving. 

What I did use PB for was to confirm the conclusion by the Oregon State group
that theropods must have had septate lungs, because all reptiles and birds
have them. I also showed that PB *cannot* be used to restore the internal
lung intricacy of other dinosaur groups and pterosaurs simply because they
have left no living descendents, which one needs before one can
phylogentically bracket a fossil to show that it retains the primitive
condition. The use of PB by Oregon State people to assert that all dinosaurs
had septate lungs is invalid. What *did* they have? Heck if I know.

Nor did I argue that the earliest ornithodirans had air-sacs. In fact, I am
pretty sure that they were absent in all but tridactyl footed theropods
because pneumatic vertebrae are absent. I showed that in tridactyl theropods
(Coelophysis on up) there is a progressive development of skeletal features
that indicate a corresponding evolution of a bird type air-sac system, which
probably reached a ratite-like level in dromaeosaurs, oviraptors, troodonts
etc.  

I did not really show that Jones may be incorrect in claiming that gut
contents are well preserved Sinosauropteryx. After all, Phil Currie - who has
carefully examined all the specimens [unlike either moi or the Oregon State
folks who seemed to have a remarkable lot to say about them although they
have only photos of one specimen to go on] - had been kind enough to do so
for me the day before:) Thanks also to L. Chiappe for helping dismantle the
wildly inaccurate restoration of the pubes of Archaeopteryx by Jones et al.
Gosh, I hardly needed to be there!  

Here I am going to add some modifications to my talk. Jones showed a slides
of one of the Sinosauropteryx slabs and claimed that it showed a croc-like
arrangement of the viscera separated from the lung cavity by a arched
transverse psuedodiaphragm. This is of course dubious in terms of
preservation, but it is also irrelevant even if true because birds also have
a diaphragm-like structure, and it too is arched at least in some birds (see
K. Schmidt-Nielsen 1972 How Animals Work). Therefore, Jones et al have no
actual evidence that dinosaurs had a croc-like respiratory complex! (They
also claimed that theropod and modern croc pubes are similar, but the
immobile, long, distally narrow pubis of Coelophysis and the short, broad
mobile croc pubis could hardly be more different). Both the skeletal anatomy
and phylogentic position of theropods completely precludes them from having a
well developed liver piston arrangement. 

What is interesting is that diaphragm-like structures are present in crocs
and birds. It is odd that birds have this structure because they seem to have
little need for one. Because a diaphragm is a derived condition not found in
most nonarchosaur reptiles (teiid lizards have them), and the croc clade
versus bird clade split occurs way back in the Archosauria, it is possible
that a psuedo-diaphragm is the general archosaur condition. There is evidence
that most basal archosaurs including the earliest dinosaurs had aerobic
exercise capacity a little above the reptile level (slightly expanded ilia,
more erect limbs, high trackway speeds, more rib mobility). It is possible
that some poorly developed form of abdominal piston ventilation was present.
This developed in various ways. Among crocodilians a it became highly
developed to the current condition as a lumbar region and mobile pubis
allowed extreme abdominal shifting. Perry has suggested that some form of
abdominal ventilation was present among ornithischians. I noted that in
ornithopods the presence of a very well developed lumbar region as well as
absence of gastralia and a procumbent pubis suggest that a mammal-like
diaphragm arrangement had developed. Tridatcyl theropods and sauropods
largely abandoned the old system in favor of air-sacs as they lengthened and
increased the mobility of the posterior ribs (opposite the development of a
lumbar region in crocs) in order to ventilate abdominal air-sacs. The
intermediate stage may have been present in intermediate theropods such as
Sinosauropteryx. Birds "remember" the old arrangement via their
psuedodiaphragms.   

Concerning long trachea in sauropods, swans have extremely long trachea not
only because they have long necks, but because the airway does a loop in the
region of the sternum! (Has to do with vocalization.) The lungs look wimpy in
comparison (see Schmidt-Nielsen 1972 again). Of course air-sacs make this
system work despite the enormous dead space. Since it is probable that
sauropods had pulmomary air-sacs, they too should have been able to overcome
the problems posed by their very long but very narrow airways without needing
elevated atmospheric oxygen, or auxilary openings at the base of the neck.   

Whose talk was the best? No two ways about it. Mary Schweitzer's. You had to
be there to fully see that there are very well preserved feathers on
Mononykus heads that are virtually identical in macro and micro structure to
the simplest modern bird feathers. Beautiful scanning electron micro photos
and everything. They are also similar in form to what Currie described for
Sinosauropteryx. Phil's talk was the most fun of the bunch, probably left the
Oregon State group a little dazed from the impact. At this time the evidence
that some theropods were truly feathered is extremely good, but the biochem
work on the composition of the structures needs to be finished before more
final conclusions can be made. 

GSPaul