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Re: definition of "reptile"

David Schwimmer wrote:

... we should recognize the classes:
> Diapsida (includes "Euryapids" Squamates, Crocodilia, Archosauromorphs,
> Crocodilia, a few miscellanea), Synapsida/Mammalia, Chelonia or Testudina,
> and DInosauria/Aves as the constituents of the former "Reptilia."  The
>  Primitive amniotes of the Pennsylvanian-Permian probably deserve a separate
> class but I have no great insight into these.
>   Nothing I've noted above is particularly novel, except the idea of compl  
> drop
> Erm "reptilia."  Comments?

John Alroy wrote:

...we could perhaps substitute  
> Reptilia for either Amniota or Diapsida. But things have just gotten  
> too confusing at this point - there are even some who would have the  
> term "reptiles" stand for Sauropsida (Diapsida + turtles). Therefore,  
> I agree that we should just drop the term completely.
I agree that the taxon Reptilia as in common use is meaningless - largely
because the Linnean system had been followed regardless of subsequent 
discoveries (like evolution!).  I currently use Reptilia to describe all
amniotes except the synapsid/mammal lineage.  My only problem concerns the
relationship of the anapsid line to the rest of the amniota - if it is true,
as suggested by cytochrome data etc, that synapsids are more closely related
to diapsids than anapsids I would be inclined to give Chelonia class status
(and retain Mammalia).  However, I am not yet convinced that there are no
synapomorphic characters supporting my Reptilia.  The obvious one is the 
uricotelic metabolism, with mammals retaining the *amphibian* type condition
of urea production.  If I could be persuaded that uric acid production was
acquired independently by anapsids then I would remove them from Reptilia.

Of course, the taxon labels and groupings are partly a matter of personal taste,
and whether you're inclined to *lump* or *split*.  As long as all taxa are 
monophyletic, so far as can be determined, there will always be room for 
alternative individual classifications (I mean, can anyone seriously see all
taxonomists agreeing?) - the important thing is to define the system you are
using if it could be ambiguous.


Tony Canning

'The past sure is tense' (Don Van Vliet)