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Re: something's wrong here: Qianosuchus phylogeny



On 9/4/07, Mike Taylor <mike@indexdata.com> wrote:
> David Marjanovic 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....)

-- 
Mike Keesey