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Re: something's wrong here: Qianosuchus phylogeny
T. Michael Keesey writes:
> > > > Really? What is the reason for knowing a priori that scleromochlids
> > > > could not possibly be paraphyletic with respect to pterosaurs?
> > >
> > > There is only one known scleromochlid, *Scleromochlus* itself, and
> > > it has autapomorphies, so the most parsimonious assumption is that
> > > it's not an ancestor of anything else we know -- never mind its
> > > geological age, which IIRC isn't older than the oldest known
> > > pterosaurs.
> > OK, but that's an accident of what we currently happen to know about
> > scleromochlids. I guess you were making a point about that specific
> > taxon; I misread your comment as meaning that no taxon ever can be
> > directly ancestral to any other -- which of course is what I was
> > disagreeing with.
> Well, for that matter, why couldn't it be an accident of what we
> currently happen to know about pterosaurs? Why couldn't we use
> pterosaurs as a paraphyletic grade that gave rise to scleromochlids?
> There's nothing to prevent a taxonomist who uses paraphyletic taxa
> from including the final common ancestor of Scleromochlus,
> rhamphorhynchoids, and pterodactyloids in Pterosauria, with
> Scleromochlus as part of a derived offshoot.
> (See, this is why higher-level paraphyletic taxa are a bad idea....)
Well, no ... you've not shown that higher-level paraphyletic taxa are
a bad idea, you've just shown one possible consequence (that one taxon
can be located inside another) and _asserted_ that it's bad. And that
consequence is really just a restatement of the definition of
paraphyly, so your statement seems to reduce to "paraphyly is bad
because of the badness of paraphyly" :-)
I still don't get this -- never have. Despite being very fond of
formal phylogenetic nomenclature (most of my published and in-press
work is on that very subject) I simply don't see what would be bad
about definitions of the form X = Y-Z where X is a paraphyletic taxon
and Y and Z are other taxa such that Z is a subset of Y. Every
argument I've ever seen against such definitions boils down to
fundamentalism: That Would Be Bad Because It Is Forbidden.
/o ) \/ Mike Taylor <email@example.com> http://www.miketaylor.org.uk
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