Re: Alligator (Archosauria) "air sacs"

[Jura <pristichampsus@yahoo.com>]

---- Original Message -----

> From: David Marjanovic <david.marjanovic@gmx.at>
> To: dinosaur@usc.edu
> Cc: 
> Sent: Monday, 20 February 2012 12:03 PM
> Subject: Re: Alligator (Archosauria) "air sacs"
> 
>>  Using gross dissections and computed tomography we studied the lungs
>>  of juvenile American alligators (Alligator mississippiensis). Our
>>  findings indicate that both the external and internal morphology of
>>  the lungs is strikingly similar to the embryonic avian respiratory
>>  system (lungs + air sacs). We identified bronchi that we propose are
>>  homologous to the avian ventrobronchi (entobronchi), laterobronchi,
>>  dorsobronchi (ectobronchi), as well as regions of the lung
>>  hypothesized to be homologous to the cervical, interclavicular,
>>  anterior thoracic, posterior thoracic, and abdominal air sacs.
>>  Furthermore, we suggest that many of the features that alligators and
>>  birds share are homologous and that some of these features are
>>  important to the aerodynamic valve mechanism and are likely
>>  plesiomorphic for Archosauria.
> 
> See, this is the kind of thing where I'm totally baffled that it wasn't 
> figured out a hundred years ago, or 120 or 130.
> 
> I suppose the logic that has prevented people from dissecting crocodilian 
> lungs 
> for so long went like this:
> 
> 1) Crocodilians are reptiles.
> 2) So, crocodilians have reptile lungs, not mammal lungs or bird lungs.
> 3) What are reptile lungs like? Let's dissect the nearest reptile and find 
> out!
> 4) We're in Europe, so let's just take the nearest lacertid, perhaps the 
> nearest "colubrid" and maybe the nearest viperid and cut them open.
> 5) <snip> <snip>
> 6) Hooray! We've figured out what reptile lungs are like!
> 7) Textbook describes and illustrates generic non-varanid squamate lung as 
> "reptile lung".
> 8) Everyone believes it is known what reptile lungs are like.
> 9) Everyone believes it is known what crocodilian lungs are like, because 
> crocodilians are reptiles.
> 
> Ceterum censeo Reptilia esse nomen del
ame, follow Joseph Collins and restrict it to Squamata or 
> Lepidosauria. Otherwise, destroy it. Kill it with fire.

+++++++++++++++++++++++++++++++++++++++++++++++

I agree with much of your presentation for why this wasn't figured out a 
century ago, but I disagree that the reason behind it was because crocs were 
lumped in as reptiles. It was because of that old Victorian view (that in many 
ways still holds today) that reptiles are all the same and all simplistic, 
primitive animals. It took this long to figure out how croc lungs worked not 
because crocs were thought to have simple reptile lungs, but because the 
concept of the simple reptile still exists.

Jason>