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>Thanks to Matt Troutman for his last couple posts on climbing. I'm   
>interested in hearing more about his thoughts.


<<I recently had a discussion about this with someone who made me 
realize that getting lighter is one possible benefit of pnuematic bones, 
but getting bigger without getting heavier is another.  All else being 
equal, a 100 Kg animal with pnuematic bones would be larger than a 100 
Kg animal without pnuematic bones. If the mass lost by pnematization 
were applied--for example--towards slightly longer legs, you could have 
a faster animal as well.>>

I'm not denying that they help lighten weight, but I doubt that this was 
their original function (we're talking about pulmonary air sacs).  Most 
authors come to the conclusion that pulmonary air sacs in birds evolved 
for respiration and I concur.  However, I cannot see that they could 
have evolved for lightening weight.  Many birds lack postcranial 
pnematization but still retain functional air sacs.  This argues against 
the "lightened weight" hypothesis.  Moreover, many flightless birds 
still retain large air sacs an postcranial pnematization.  Limb 
pnematization by use of avian air sacs is unlikely in theropods and 
other dinosaurs.  Never once has a pnematopore or pnematic foramen in a 
limb bone been described for a non-avian (non-ornithurine if the humeral 
pnematic foramen in _Confuciusornis_ is a fake) dinosaur.  Simply put, 
there seems to be no pulmonary invasion of the long bones in dinosaurs.  
Probably the bones were simply hollow, which is something very different 
from pnematization.  Buhler (1992) stressed this repeatedly.  Very 
interestingly, Buhler argued that the long bones of the London 
_Archaeopteryx_ were hollow.  

<<Yalden considered it a moderately close analogy, but as Matt indicated 
he didn't push the analogy beyond trunk climbing; for good reasons in my 
opinion.  Even though the flying lemur is completely arboreal, it is 
actually very awkward in the trees. Its large patagium and non-opposable 
thumbs make movement among the branches very difficult. In fact, they 
often get around in trees by hanging upside down by their claws like the 
South American sloths. Archie was probably more agile among the branches 
and was certainly equipped to pursue cursorial activities as well.>>    

Yes, I only considered the analogy of _Cynocephalus_ and _Archaeopteryx_ 
to be only restricted to the trunk-clombing habits in my origninal post.  
But now that you bring it up _Cynocephalus_ can provide further analogy 
to _Archaeopteryx_.  Besides the obvious phylogenetic analogies, 
_Archaeopteryx_ and _Cynocephalus_ conform well to each other in matters 
of manual structure, pectoral structure, and other features.  Both 
creatures appear to be in early stages of flight (_Archaeopteryx_ is 
further up that ladder than _Cynocephalus_) so they can be considered 
further analogs.  The wide gliding membrane of _Cynocephalus_ can be 
loosely compared to the wing of _Archaeopteryx_.  Both share a similiar 
proportion as compared to the body and both can be viewed as a 
maladaptive state because they both would impede the progress of 
climbing.  Many recent authors have considered the large wing of 
_Archaeopteryx_ as evidence against its ability to climb quadrapedally 
(Peters 1985; Peter and Gorgner 1992; Richetal 1985; & Padian and 
Chiappe 1998) because it would presumeably get in the "way".  However, 
many gliding mammals (eg. _Petaurus_, _Cynocephalus_, etc.) have large 
gliding membranes that can easily make climbing hard to achieve (I have 
seen firsthand evidence of this in my captive _Petaurus_, which has a 
large gliding membrane that appears that it would easily get in the way, 
but doesn't).  

I cannot make a definite stand on the ability of _Archaeopteryx_ to hunt 
cursorially.  Even though the hallux is positioned rather dorsally on 
the tarsometatarsus, I still can see it easily it as a detriment.  The 
lack of fraying on the tail and wings (Feduccia 1993) also argues 
against cursorial habits, even if occasional.  Plus, there is Martin's 
(1991) evidence that _Archaeopteryx_ may have had a slightly splayed 
arrangement to the hindlimbs (this has been critisized often and I don't 
stick by it strictly).  

Anyway, I think that the evidence is good for a close analogy of 
_Cynocephalus_ and _Archaeopteryx_.

Matt Troutman

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