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Re: Lumping Spinosauridae Redux



> Date: Tue, 21 Sep 2004 04:55:53 -0700
> From: Mickey Mortimer <Mickey_Mortimer111@msn.com>
> 
> My position is that the most important thing when deciding whether
> to make two species congeneric is the monophyly of the resulting
> genus.

The problem with that position is that, by induction, everything
that's ever lived is a single genus.  Example: suppose we say that we
have no other specimen phylogentically between _Brachiosaurus
altithorax_ and _"Giraffatitan" brancai_, and for that reason sink
both species into _Brachiosaurus_.  Then we observe that the immediate
outgroup to _Brachiosaurus_ is _Sauroposeidon_, so nothing separates
them phylogentically and we therefore sink _Sauroposeidon_, so that
_S. proteles_ becomes _Brachiosaurus proteles_.  But the outgroup is
now _Cedarosaurus_, so we sink it into _Brachiosaurus_ and
_C. weiskopfae_ becomes _Brachiosaurus weiskopfae_.  But then ...
[skip a bit, brother]
... But the outgroup is Plantae, so we sink we sink plants into
_Brachiosaurus_, and our work here is done :-)

To be clear, I fully realise that you are not advocating going to
these extremes.  But I do think this shows that you can't just rely on
monophyly of the new, broader genus when deciding whether one should
be sunk into another.

I guess we could say that monophyly of A-together-with-B is a
necessary but insufficient condition for sinking A into B.

 _/|_    _______________________________________________________________
/o ) \/  Mike Taylor  <mike@indexdata.com>  http://www.miketaylor.org.uk
)_v__/\  "I'm not a lawyer; I have, however, done some dumb things"
         -- Jane MacDonald.

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