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More on whether Reptilia is a useful taxon:
Responding to Stan Friesen:
>>>"Reptilia is a perfect valid paraphyletic taxon.<<<
No, I don't agree.
First, I'm by no means a rabid cladist. In fact, by pure
cladistic logic, allowing no paraphyly, we're crossopterygian
But, the original concept of Reptilia as generally understood
is in no way the modern group. We all can agree that the
Synapida are far removed from all the other basic amniotes, as
are the turtles and (probably their ancestors) the procolophonids
More so, the dinosaur/avian clade may be as far away
phyletically _and_ morphologically from the remaining "reptiles"
(i.e. minus turtles, other "anapsids" and synapsids) as are any
other amniotes. So the term "reptile" hardly applies to them.
My point is, our remaining more-or-less-related core of
"reptiles" is so different from the original usage of the term,
that "Reptilia" becomes virtually meaningless.
In my VP classes I do not use it except as an historical note.
Nevertheless, I do accept logical cutoffs between, say,
primitive Synapsids and Mammals, avian and non-avian dinosaurs,
recognizing that all taxonomy is interpretive and adaptive.
>>>"Let us take an example - birds.....How to do this? In fact
how to seperate Aves at *any* taxonomic level?"<<<
Easy, define autapomorphies, such as presence of pygostyles vs.
tails, feathers, carinae or carinae as a plesiomorphy, etc. and
you've separated avian from non-avian dinos. The problem is
simply reduced to whether or not they are a Class. I think the
evidence suggests not. Dinosaurias should include Aves, but as a
subclass; or betterm Dinosauria could be a superclass with
Dinosaurxxxx and Aves as Classes. They do it all the time with
Aganathan "fish" (check any recent work).
Replying to John Alroy:
>>>"It seems to me that instead of preserving all sorts of
paraphyletic higher groupings like "Reptilia," we should simply
get rid of the entire ranking system itself."<<<
That's a bit too extreme. We can all acccept that Linnean ranks
are artificial, and there for purposes of communication.
>>>"Actually, I do agree that there is a place for paraphyletic
groups in paleontological classifications. However, I think they
should be avoided when this is reasonable, and perhaps restricted
to the genus level, where I really find it hard to see how we can
I agree, but even taxa to the Ordinal level are OK if we accept
them as artificial lumps.
Again, my basic argument was that "Reptile" was garbage can term
and it, alone, needs to be dumped as a vertebrate class.
A point I make to my VP classes is that any primitive
(whatever that means) amniote will basically look lizard-like in
overall body plan, and hence "reptilian." This is the basic
amniote gross shape: tetrapodal, elongate, long tail,terminal
head, etc. This plesiomorphy of amniotes led to the concept of
Reptilia, which we now know is grossly paraphyletic.