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Re: Adios, "Brachiosaurus" brancai

2009/9/11 Tim Williams <tijawi@yahoo.com>:
>> 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):

See?  Told you I didn't know enough to comment!  :-)

>> 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.

Sorry, I obviously wasn't making myself clear here.  I am NOT
advocating that someone should go ploughing into Psittacosaurus and
moving each species to its own genus "just in case"!  All I am saying
is that when you name a new species of an existing genus, you are
betting the new taxon's name on your phylogenetic hypothesis.  That
might have been a reasonable thing to do in 1800s, when we only knew
about a handful of dinosaurs; but here we are with 600 genera or
however many it is now, and with new phylogenies coming out ever five
minutes that throw all the old ideas up in the air.  It would be
interesting to run the stats(*) but I'm guessing that more than half
of all dinosaur species originally named within an existing genus have
subsequently been renamed; and I bet that if cladistic analyses were
run at the species level rather than ASSUMING genus monophyly, we'd
find ourselves reshuffling a lot more.

So when naming a new species in 2009, why even offer up that hostage
to fortune?  Better to give it a uninomial, and let the ashes fall
where they may.

> 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.

True enough, and a good point.

But remember that we know a lot more now that those goober-heads back
in the 19th century knew.  For a start, we know to avoid creating
nomina nuda, and more about how to avoid raising names that end up as
nomina dubia.  There is no way that most of those Cetiosaurus species
would be named if discovered today.

>> 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_)."

Oh, I did wonder how "This isn't a comp" was going to finish :-)

Well, some time soon I'll be shoving Sauroposeidon and the Archbishop
into the matrix.  When I do, I guess I'll report on SV-POW! (and maybe
post a note here for those who are misguided enough not to read
SV-POW! regularly).  The other will have to wait.