RE: Stegosaur volume of Swiss Journal of Geosciences

[Tim Williams <tijawi@yahoo.com>]

Michael Mortimer <mickey_mortimer111@msn.com> wrote:


> Long postorbital horns are only known in ceratopsids and
> their close sister taxa (Zuniceratops, Turanoceratops,
> etc.).  


True enough.  But which one is _Ceratops_: "ceratopsid" or "close sister taxon"?


> I was countering your statement that Ceratopsidae should
> have never been named by Marsh because Ceratops was so
> fragmentary. 


I didn't have Ceratopsidae in mind when I made that comment.  After all, this 
was the 19th century, so I think we can give Marsh the benefit of the doubt.  I 
was alluding to families named in more recent times that began as monotypic 
families - like Mussauridae or Agustiniidae or Aberratiodontidae.  The fact 
that these families were named makes them 'available' - which I don't always 
think is a good thing.  It's like you're rewarding workers who erect new 
families willy-nilly.  Other workers are more restrained, and don't 
automatically erect new families whenever they discover a particularly 
distinctive new taxon.  _Eoraptor_ and _Eocursor_ and _Mononykus_ could have 
been granted their own families (because they clearly didn't belong to existing 
ones), but weren't.


> Instead of ditching Ceratopsidae, why don't we define it in
> a way that will include Ceratops?  "Ceratops montanus <-
> Protoceratops andrewsi, Leptoceratops gracilis" or
> something?  


Yes, I'm fine with that.  However, that means you have to go through the 
motions of including _Ceratops montanus_ in a phylogenetic analysis.  This 
seems like a pointless exercise - all this extra effort just to have _Ceratops_ 
remain as the name-giving taxon.  


> Allosaurus fragilis is probably indeterminate within
> Allosauridae based on its holotype. Neovenator should be a
> carcharodontosaurid under that family's definition, and
> Neovenatoridae was based on the results of a single
> dataset.  Coelophysidae was also based on probably
> indeterminate material that had to be exchanged for a
> neotype.  Iguanodon and now it seems Stegosaurus were based
> on material
w
> Iguanodon is probably not the same as the original Iguanodon
> (likely to be Kukufeldia).  The "Brachiosaurus" that is
> well known is Giraffatitan.  Pachycephalosaurus' type is
> just a skull roof that could prove indeterminate once we
> have more complete pachycephalosaurines.  As far as I know,
> there hasn't been an in depth analysis of Diplodocus or
> Camarasaurus species in two decades, so who knows how longus
> (several caudals and chevrons) and supremus (8 vertebrae)
> will hold up.  These kind of examples are why we need
> strict priority-based taxonomy which does not fall when its
> eponym is found to be an undiagnostic member, as opposed to
> some subjective, authority-based system where things get
> renamed or lose their type status whenever someone thinks
> they're undiagnostic.


No, I think for the sake of taxonomic stability that we need to maintain 
well-known genera, even when they are found to have inadequate type species.  
That's why I think it was a good idea to replace the type species of 
_Iguanodon_, and to do the same for _Stegosaurus_. 


You mention that _Allosaurus_ and _Coelophysis_ were based on indeterminate 
holotypes.  Well, a neotype was designated for _Coleophysis_; and a neotype has 
been proposed for _Allosaurus_:

http://gspauldino.com/images/BZN67%281%29Case3506.pdf


I know you know this; but I'm just mentioning these examples to show that 
switching the type species and/or type specimen is an integral part of 
taxonomy.  It is not 'subversion'.  Not all taxonomy is priority-based.  
Sometimes entirely subjective decisions are made in order preserve taxonomic 
stability.


Should _Diplodocus_ and _Camarasaurus_ be found to be established upon 
indeterminate type species, then I'm sure a new type species will be proposed 
for these two genera.  This is preferable to either genus becoming a nomen 
dubium, considering how entrenched they are in the literature.


> As the above examples show, what seems like a justifiably
> valid taxon now may not be judged that way in the future. 
> 
 any more
> valid in 2100 than Marsh's views are now.  Sure Sinraptor
> dongi's holotype is rather complete, but there are questions
> as to its validity compared to the earlier named hepingensis
> and Yangchuanosaurus.  Yangchuanosaurus was named over a
> decade before Sinraptor, and has a more complete sacrum and
> tail.  Under your system, why not use "Yangchuanosauridae"
> as the proper name for the family?  It's all subjective
> anyway, so you can't say I'm wrong that the 15 years of
> genus priority, possibility of Yangchuanosaurus being the
> correct genus name, and more complete sacrum and tail trump
> Sinraptoridae being named and defined first and being based
> on a specimen with preserved manus and pes.  


All I'm saying is that Sinraptoridae is a better choice than 
Metriacanthosauridae for this clade.  I'm not saying that the best-known genus 
should *always* be the name-giver.  All I'm saying is that some families were 
named after very poorly known genera, and I don't think priority-based taxonomy 
is always helpful for family-level clades.  And priority-based taxonomy is not 
the gold standard anyway - otherwise we would use Dryptosauroidea (Marsh, 1890) 
in place of Tyrannosauroidea (Osborn, 1906).



Cheers

Tim