Re: Air sacs in extant non-avian reptiles?

[Ronald Orenstein <ornstn@home.com>]

At 09:33 AM 31/07/00 -0400, ELurio@aol.com wrote:
> Have you actually compared a pidgen with a gecko? The differences are
> enormous!!!! The small group of physiologists  n fact accounts for
> practically all of them working today, not to mention every single
> orthinologists. Birds are as much reptiles as they are fish.

Well, speaking as an ornithologist I agree with the last statement!  Birds 
are both reptiles and fish, of course, just as we are both synapsids and fish.

The question of whether or not to recognize Aves as a class strikes me, 
though, as (a) moot and (b) certainly not to be decided on the basis of 
similarity.  For example, compare (say) a lungfish and a bluefin tuna - as 
different, I would think, as geckos and pigeons (if not more so) and yet 
both members of the traditional "class" Osteichthyes.

The point is that in a phylogenetic sense, even if we only consider living 
animals, a crocodile is more closely related to a pigeon than to a gecko 
-whatever their level of similarity.  Therefore if crocodiles are reptiles 
along with geckos, birds must be too.

However, ornithologists do generally support class status for Aves - but 
not, I think, because they think thee is any great inherent truth to the 
notion.  It is a a matter of convenience, because if you are going to 
reduce Aves to (say) ordinal level you must reduce the ranks below it and 
this becomes confusing, as most of us are used to thinking of modern birds 
as comprising twenty or thirty orders, not one.

Of course any heirarchical system like Linnaeus's must be arbitrary when 
imposed on a continuous evolutionary stream.  For that reason I rather like 
the idea of doing away with the heirarchies altogether.  Birds certainly 
consist of a monophyletic taxon, and whether you call it Aves or something 
else, or call it a Class, an Order or nothing at all, that fact does not 
change.  Reptiles including birds do too - but reptiles not including birds 
do not.  Neither do bony fishes if tetrapods are omitted. As long as we 
recognize this, and we all know what we are talking about in any given 
context, I do not think the rest matters, including whether birds are 
called a class, or whether geckos are called non-avian reptiles.
--
Ronald I. Orenstein                           Phone: (905) 820-7886
International Wildlife Coalition              Fax/Modem: (905) 569-0116
1825 Shady Creek Court
Mississauga, Ontario, Canada L5L 3W2          mailto:ornstn@home.com