Re: Adios, "Brachiosaurus" brancai

[Tim Williams <tijawi@yahoo.com>]

Mike Taylor <mike@indexdata.com> wrote:


> 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.


I do think Mike makes a good case for making the east African _brancai_ a 
separate genus from the North American _altithorax_.  Apart from the reasons 
stated in Taylor (2009), this also dispels the much vaunted faunal association 
between the Tendaguru and Morrison Formations.  For a long time, these two 
formations were thought to share a common fauna, which (in turn) was cited in 
support of a privileged connection between east Africa and western North 
America during the later Jurassic.  With other "common" Tendaguru-Morrison 
genera likewise split up (_Barosaurus_/_Tornieria_, 
_Dryosaurus_/_Dysalotosaurus_), it was only a matter of time before 
_Brachiosaurus_ went the same way.  


However, I certainly don't agree that all genera should be monospecific.  Using 
that logic, _Psittacosaurus_ would have to be split up into six or seven (or 
whatever) genera, which does not seem justified.

 
> 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.


The phylogeny featured in Taylor (2009) (Figure 6) only includes two 
traditional brachiosaurid OTU's: _altithorax_ and _brancai_.  This isn't a comp
 relationship would still be recovered for _altithorax_+_brancai_ if a larger 
sample of taxa were included in the analysis, including those genera mentioned 
by Mike (_Sauroposeidon_, _Cedarosaurus_, _Venenosaurus_).




Cheers

Tim