Re: Adios, "Brachiosaurus" brancai

[Tim Williams <tijawi@yahoo.com>]

Mike Taylor wrote:


> Well, I don't know anywhere near enough about ceratopsians
> to comment
> intelligently on that particular case.  But are we
> really confident
> that the complex of, what is it now, eight or nine
> Psitracosaurus
> species is monophyletic with respect to the various other
> basal
> ceratopsians that have been placed in other genera? 


I believe so.  Not that this is the final word or anything, but one recent 
study noted that the genus _Psittacosaurus_ is extremely conservative.  Sereno 
et al. (2009; Proc. R. Soc. B doi: 10.1098/rspb.2009.0691): 


"Psittacosaurus is the most diverse dinosaurian genus with at least nine 
species after a conservative taxonomic revision (Sereno 2009). The genus is 
speciose because nearly all taxonomic differentia are limited to relatively 
minor tooth or cranial bone ornamentation. Variation in tooth replacement rate 
or jaw morphology is negligible compared to that seen in closely related basal 
neoceratopsians. The psittacosaur postcranial skeleton, in addition, is 
remarkably uniform."


If Lukas's analysis holds up, then it would be an argument to sink 
_Hongshanosaurus_ into _Psittacosaurus_, rather than create at least eight new 
psittacosaurid genera.


> Because if not,
> we're heading for a Great Renaming, and those are never
> fun.  Whereas
> had those species all been placed in different genera in
> the first
> place, then their names would be unaffected by
> phylogenetic
> reshuffling.  That seems to me to be obviously A Good
> Thing.


I tend to think that a "Great Naming" is only predicated on a profound 
phylogenetic reshuffling, rather than (as you seem to be suggesting) a 
pre-emptive strike should a phylogenetic shuffling ever occur.  In other words, 
I think it's preferable to assess these matters on a case-by-case basis.


In the case of _Brachiosaurus_ vs _Giraffatitan_ (which sounds like a divorce 
case, which in a sense it is), there is adequate evidence on morphological and 
biogeographical grounds that the two genera should be treated as separate 
genera.  I agree with you here.


By contrast, in the case of _Psittacosaurus_, I'm not sure a phylogenetic 
re-shuffling is inevitable, especially with respect to other ceratopsians.  The 
genus is exceptionally 'tight', on morphological (see above) as well as 
biogeographical grounds.


> (One multiple-species dinosaur I DO know about is
> Cetiosaurus, which
> had thirteen(!) species before it was revised by Upchurch
> and Martin
> (2003).  They reduced it to ONE valid species, C.
> oxoniensis, with the
> others being nomen nuda, nomen dubia, or members of
> distantly related
> sauropod groups.  I'm sure the situation with
> Psittacosaurus is
> nowhere near so dire, as Cetio had to carry an awful lot
> of
> 19th-Century taxonomic baggage, but it's a cautionary tale
> nonetheless.)


The situation with _Psittacosaurus_ is very much different to _Cetiosaurus_.  
For _Psittacosaurus_, there are eight or nine ostensibly valid species (= those 
remaining after the nomina nuda, nomina dubia, and junior synonyms have been 
removed from the tally).  


I also think your _Cetiosaurus_ example is a cautionary tale from another 
perspective.  If every one of these _Cetiosaurus_ species had been granted its 
own genus at the time of their naming (which is in keeping with your uninomial 
argument), think of how many 'bad' genera we would be forced to deal with now.  
Those 12 invalid species you mention would be 12 invalid genera.  It's a little 
scary to consider how many new genera _Triceratops_ and _Plateosaurus_ would be 
split into, given the plethora of named (as opposed to valid) species there are 
in the literature.


> Like I said in the SV-POW! post, others are working on the more
> general problem of basal titanosauriform phylogeny.


Yep, my comment was not a reflection at all on your paper, which was not 
concerned with titanosauriform phylogeny.  I highlighted this, but that 
particular line inexplicably disappeared from my message.  I was actually 
lending support to the idea that the sister taxon relationship between 
_Brachiosaurus_ and _Giraffatitan_ could be broken up by a more expansive 
analysis that specifically included brachiosaurid OTUs.  Here is the complete 
paragraph, with the missing line put back in:


"The phylogeny featured in Taylor (2009) (Figure 6) only includes two 
traditional brachiosaurid OTU's: _altithorax_ and _brancai_.  This isn't a 
complaint; but I wonder if a sister taxon 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