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Re: Australodocus a titanosauriform and other new papers



Jaime Headden <qi_leong@hotmail.com> wrote:

> Whitlock's issue is the same one I had (here: 
> http://qilong.wordpress.com/2011/03/11/systematic-originalism/) when dealing 
> with Taylor resurrecting Paul's otherwise unused *Giraffatitan*: The use of
> *Giraffatitan* superimposes the idea or concept of "genus" on the discussion 
> of diversity; that "brachiosaurids" are _more diverse_ than previously 
> argued; that *altithorax* and *brancai* have a lot of
>  differences, but that *altithorax* vs. *brancai* is "insufficient" to 
> recognize this; and that no analysis published supports placing *brancai* 
> anywhere else than next to *altithorax* -- and when highlighting
> this latter argument, Taylor failed to support it when splitting them and 
> then testing them cladistically.


Yes, this relationship (having _Brachiosaurus_ and _Giraffatitan_ as
sister taxa) was found to be the most parsimonious result.
Nevertheless, Mike also found that only a single further step is
required for _Giraffatitan_ to fall closer to Titanosauria than to
_Brachiosaurus_.


Whitlock thought it was appropriate to sink _Giraffatitan_ into
_Brachiosaurus_, and keep _Australodocus_ standing as a separate
genus.  This is actually a phylogenetic hypothesis; but he didn't
actually test it.  The way to do this would be to treat
_Brachiosaurus_, _Giraffatitan_, and _Australodocus_ as separate OTUs,
instead of invoking Whitlock's supine argument that genus and names
are mere 'signifiers', so it doesn't matter what we call them.  (It
would have helped to throw some derived titanosaurs into the analysis
too.)


>  The argument that we are better at facilitating communication by using a 
> binomen, in this case a genus-species couplet (as used by Taylor when 
> resurrecting the taxon name), fails because the
> objective value of the genus is inherently tied to a failed systematic 
> system, the Linnaean System.


True - up to a point.  As far as genera are concerned, the binomial
system is subjective  - but it is not "arbitrary" (as claimed by
Whitlock).  If you're going to lump _Giraffatitan_ into
_Brachiosaurus_, why not throw _Sonorasaurus_ in too?   Based on what
is known of it, _Sonorasaurus_ is morphologically more similar to
_Brachiosaurus_ than _Giraffatitan_ is.  Witlock's argument that
tradition should carry the day is spurious, and goes against the grain
of phylogenetic taxonomy.



Mickey Mortimer <mickey_mortimer111@msn.com> wrote:

> When we discussed this on your blog, we narrowed our disagreement down to the 
> fact that you don't see genera as clades.  But I can assure you that Taylor, 
> Williams, myself and most others on here
> DO think of genera as being clades.  Thus retaining brancai in Brachiosaurus 
> implies it is in a clade with altithorax to the exclusion of Sonorasaurus, 
> Cedarosaurus and every other named genus.  And
> THAT's the reason we all have a problem with it.  You may view genera as just 
> Linnaean labels, but most of us see them as implying monophyly.


Yes.  Exactly.






Cheers

Tim