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re: definition of "reptile"
From: "Paleontology Columbus College, Georgia"
> I've stayed out of discussion on "mammal-reptile" nature because I have
> nothing additional to add. However, I notice that the term "reptile"
> by everyone. I suggest the term is meaningless and invalid because the
> original Linnean definition and concept is irrevocably changed. I suggest we
> substitute "Diapsida" for "Reptilia" and separate all the papaphyletic groups
> into proper lineages: thus, we should recognize the classes:
Well, that is the way the cladists would do it.
However, the rejection of paraphyletic taxa is questionable.
There are a number of reasons, both practical and theoretical,
to continue to use paraphyletic taxa.
Reptilia is a perfect valid paraphyletic taxon.
One problem with the cladistic criterion for taxa is that it
requires either that major adaptive shifts be ignored in the
classification, *or* that the morphologically conservative
groups related to the derived group be broken up into numerous
extremely small, scarcely differentiated taxa.
Let us take an example - birds.
Birds are the result of a major adaptive shift, and consequently
have a large suite of new (apomorphic) adaptive characters.
They are also a large, higly diverse group. This suggests that
they ought to be distinguished at a fairly high taxonomic level.
How to do this? In fact how to seperate Aves at *any* taxonomic level?
Well, the taxa Diapsida, Archosauromorpha,
Archosauria, and Dinosauria, if defined in the cladistic sense,
*must* all *include* Aves. To seperate the birds, it is necessary
to break things down further - *much* *further* - if one is to
maintain the cladistic rule. The living diapsida must first be broken
into Lepidosauria and Crocodilia. Then, assuming the most widely
held phylogeny is correct, Dinosauria must be split into at least
*seven* taxa of no lower rank than the Aves taxon! This produces
the silly result that Ornithomimosauria, a group of forms so similar
to one another they are almost indistinguishable to the layman,
must be at least the the same rank as Aves!?!?
The peace of God be with you.