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RE: Adios, "Brachiosaurus" brancai
Mike Taylor wrote:
Aside from simply describing the differences between *brancai* and
*altithorax*, distinguishing *b* and *a* from one another and placing them
differentially in a matrix, and comparing the result to other analyses? Three
pages, and one specific paragraph justifying the name (which actually does
nothing to justify the generic status of *Giraffatitan*).
There are two reasons:
1. Aforementioned lack of distinction between *brancai*/*altithorax* and
*Giraffatitan*/*Brachiosaurus*, which leads us into defining "genus" and
species, and defining how to determine the difference. The "reason" being:
"All elements sufficiently well preserved in both species, then, exhibit
distinct differences, and generic separation is warranted since the two species
are more different from each other than, for example, Diplodocus and Barosaurus
Marsh, 1890." (Taylor, pg 798)
The choice here was to support a genus (which is as yet undefined in the
paper) instead of, say, sinking *Barosaurus* into *Diplodocus* (which already
at this point contains *Seismosaurus*) or some such. This tends to call into
question a lot of such splitting and even lumping, but there is no way to argue
against these aside from the issue of decrying either redundant nomenclature,
or excessive nomenclature where no information is gleaned from its use.
2. The analysis of Taylor supports *brancai* and *altithorax* as sister taxa.
Why is it needful to split them when the very analysis run to support
distinction does not move these taxa around relative to the somphospndylian
titanosauriforms? Yes, one tree after reducing the parsimony of the analysis
will find the two taxa split stemwise rather than conjoined nodewise, but this
analysis does not support this. Distinguishing based on analysis with robust
support of relationship of one split-off taxon to a group not including the
other is seemingly ample support for such naming, and as an example results in
*Tornieria* and later *Janenschia* as split from *Barosaurus* whence they were
refered from generic ambiguity (instead of coining a containing name on the
spot "equivalent" to *Barosaurus*).
The prefered fiction (a matter of perspective, one would say) that Tendaguru
and Morrison taxa related to the same general area of phylogenies to one
another should not bear the same names is a fiction only perpetuated by
distinguishing the fiction of the genus, which Taylor furthers by blatantly
arguing for their use.
Mike and I actually agree on the ideal system, but I see the issue as
unsettlable until we can do away with ranks compeletly. Mike has attested to in
the past that there is some sense of utility for a "family" and "genus" and in
this case, the system of concentric containing taxa and the rank based system
of the preference of the genus, its refinement to the species, and then its
containment by the family, order, class, etc. are incompatible when seen from
the perspective of the need to support a taxon by its rank, which is what I
feel is the issue here. I have no problem with *Giraffatitan* (and I agree with
Paul that it is indeed a fine name), but I do feel that excessive taxonomy for
the sake of a "feel good move" is excessive.
So with that, I leave this latest installment of the Great Genus Debate (a
subset of the What is a Rank? Battle in the Phylogenetics-Linnaeism War) with a
hearty kudos to Mike for a well done paper and excellent presentation on the
ample relook at *altithorax* and its distinction from *brancai* (which is real,
don't doubt it) and much needed attention for the former.
Jaime A. Headden
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> Date: Thu, 10 Sep 2009 22:58:52 +0100
> From: email@example.com
> To: firstname.lastname@example.org
> CC: email@example.com
> Subject: Re: Adios, "Brachiosaurus" brancai
> At the start of this thread, I wrote:
>> (And now we get into another discussion about what a "genus" is ...)
> And lo! It was so!
> 2009/9/10 Jaime Headden :
>> On a purely technical level, I do think it is hasty to dismiss the identity
>> of *"Brachiosaurus" brancai* as a species of *Brachiosaurus*, for a few
> Hasty? Read the 20 meaty pages and then tell me it's hasty!
>> Complexing the genera by recognition of *Giraffatitan* (which workers are
>> still permitted to ignore) is not substantiated by a study that forces
>> *brancai* closer to any other taxon other than *Brachiosaurus altithorax*,
>> and from what I understand (unless Mike is willing to email me a copy of the
>> paper) based on the SV-POW! post, the study receives a polytomy of
> The PDF is prominently linked, twice, from the SV-POW! post. Here's
> that link again:
> The phylogenetic analysis follows that of Harris (2006) except in
> splitting the compound "Brachiosaurus" OTU into separate OTUs for
> Brachiosaurus proper and Giraffatitan. In all MPTs, Brachiosaurus and
> Giraffatitan form a clade; but only one further step is required to
> make Giraffatitan a somphospondylian.
>> The questiuon here is: How is this information better conveyed by placing a
>> species into a genus, versus placing all the species into a single genus?
>> What does *Brachiosaurus* mean if it will only ever be synonymous with
>> *altithorax*? The utility of nesting taxonomy is that containers can hold
>> more than one internal "object" or name, and it seems a waste to support
>> this for some tax and not others (especially since I suspect there is a
>> drive to have genera -- a "species" is just not sexy enough to care about,
>> and this issue plagues the *altithorax* problem).
> Genera are better than species because they are uninomials. (Well: a
> name like "Xenoposeidon proneneukos" is a binomial by convention, but
> the reality is that its a uninomial that happens to have a space in
> the middle.) I thought we all agreed that uninomials are better than
> binomials because it's dumb to encode your phylogenetic hypothesis as
> part of the name. I guess you'd be happy with the generic name
> Giraffatitan if my phylogenetic analysis had recovered it as a
> somphospondylian; but then what do you do when Jeff Wilson's analysis
> comes along and recovers it closer to Brachiosaurus after all --
> rename it back to B. brancai? And if it is recovered as the sister
> taxon to Euhelopus zdanskyi, are we going to rename it Euhelopus
> brancai? Let's just not go there. Monospecific genera, please! Keep
> phylogeny and nomenclature separate.
>> So my question is this: Why do we need *Giraffatitan*, and cannot have a
>> *Brachiosaurus proteles* etc.?
> If you want, you can put Giraffatitan and Sauroposeidon -- and
> Cedarosaurus and Venenosaurus -- all into Brachiosaurus. And you can
> put Opisthocoelicaudia into Saltasaurus, and Nemegtosaurus into
> Rapetosaurus; and then you can put Rapetosaurus into Saltasaurus too,
> since they are now sister taxa, and so on back down the tree till we
> put Brachiosaurus (i.e. what we now call Brachiosauridae) into
> Saltasaurus, too. While you're at it, put Barosaurus into Diplodocus.
> And so on until you consider Homo synonymous with Brachiosaurus.
> (Hey, I wouldn't mind being Brachiosaurus sapiens!) If you want to
> avoid this degenerate conclusion, you have to draw a line somewhere.
> I am drawing it between Brachiosaurus and Giraffatitan.
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