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Re: [RE: Air sacs in extant non-avian reptiles?]



Unfortunately reptilian air sac study is nowhere near as deeply covered as
avian air sac study, but I'll see what I can do.

Chameleons - 

Various chameleon species are known to have large partitioned lungs that
extend throughout the entire body. I don't know how "air-sacy" they are nor
can I knock off a species list either; unfortunately.

The purpose of these bodily lungs is probably very different from that of
birds, since no chameleon is known for its high endurance (or reasonable
speed). It seems that they mostly use them for long bouts of "puffing" where
they inflate their bodies and do a lacertilian strut.

Snakes -

32 snake species are known to have air sacs in their bodies and once again
there really is not too much research regarding these tracheal air sacs. 

One species known for its air sacs (and one in which research has been done)
is _Gonyosoma oxycephalum_ the red-tailed rat snake.  The snake's air sacs
compose about 16% of the body length and are divided up into 15 separate
chambers that extend from the edges of the tracheal cartilage. Each sac
connects to its neighbour and when inflated, gives the snake a fat neck
appearance (a lot like the fat neck seen in varanids, but no real relation). 
Air sac inflation is optional with the snakes able to inflate their lungs
without inflating their air sacs and when they do inflate the sacs, the lungs
still function normally.

The purpose is anybody's guess. Of those 32 snake species known to possess
sacs, all but one are colubrids (the wild card here is _Ophiophagus hannah_,
the only cobra known to have them) and the majority appear to be arboreal. The
occurence of air sacs does not seem to follow any-one evolutionary line as
some of the closest relatives to _Gonyosoma_ lack air sacs (_O.hannah_ being a
prime example) while other, more distant relatives, do have them.

Defense seems a good reason for the sacs, but the result (fat neck) is easily
duplicated by several "sac-less" snakes so there is probably more to it.

As I said, there hasn't been that much work done in this field (the curse of
being a herp enthusiast and yet one of the joys of being a herpetologist), but
I'll give you what I can.

Brattstrom, H.B. 1959. The functions of the air sac in snakes.                
                  _Herpetologica_ 15:103-104.

Lillywhite, Harvey B. 1999. Defensive Neck Displays in Snakes _REPTILES_      
                       Vol 7, 9:27-30

Noble, G.K. 1921. Snakes that inflate. _Natural History_ 21:167-171.

Young, B.A. 1991. Morphological basis of "growling" in the king cobra         
             _Ophiophagus hannah_. _Journal of Experimental Zoology_          
        260: 275-287.

Young, B.A. 1992. Tracheal diverticula in snakes: possible functions and      
             evolution. _Journal of Zoology_ (London) 227:567-583.


Jura


P.S. Regarding the whole taxonomy fiasco. In the immortal words of that
vulture from Disney's The Jungle Book: "Aw now don't start dat again!"

Jurassosaurus's Reptipage: A page devoted to the study of the reptilia:

http://reptilis.webjump.com

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