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RE: Greg Paul's new (or newly named) iguanodonts
David Marjanovic wrote:
> Now this is interesting -- a phylogenetic definition for the name of a
> paraphyletic taxon! That's the first time such an idea is presented
Well, some fella named "Mike Taylor" suggested it (though not yet in print) ...
... and he was serious. :-)
BTW, I have no conscientious or ideological objections to naming paraphyletic
taxa, in principle. But I suspect that in practice these paraphyletic groups
could become more trouble than what they're worth. By definition, paraphyletic
groups could only be 'diagnosed' by characters they *don't* have, rather than
characters they do have. But the distinction could be lost by those who are
unfamiliar with phylogenetic nomenclature. Thus, these paraphyletic groups
could be mistaken as clades, and used (and abused) as such in
phylogenetic/evolutionary discussions. They would be not only misleading, but
potentially dangerous too.
For example, the paraphyletic group "Thecodontia" might be revived in
discussions on bird origins, especially by the tiny minority who advocate a
non-dinosaurian origin of birds (and who, as it is, tend to play fast and loose
with phylogenetic concepts). We could see a paper containing sentences like
"Birds (Aves) probably evolved from Thecodontia, given that primitive birds
share the following characters with thecodonts..." Naming paraphyletic groups,
no matter how practical-minded and honorable the motive behind it, could
further confuse the distinction between derived/apomorphic and
primitive/plesiomorphic characters. I think the current practice of using
(admittedly cumbersome) terms such as "thecodont-grade archosauromorph" or
"non-dinosaurian archosauromorph" helps ensure that groups like "Thecodontia"
continue to be *excluded* from phylogenetic discussions.
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