RE: Ceratops (was RE: Pterosaur diversity (was: Re: Waimanu))

[Michael Mortimer <mickey_mortimer111@msn.com>]

Tim Williams wrote-

> So the size of the horn cores is useless for diagnosing 
> Chasmosaurinae/Ceratopsinae.  Thus _Ceratops_ cannot be demonstrated to be 
> a "ceratopsine", and it cannot be demonstrated not to be a centrosaurine, 
> or a non-ceratopsid ceratopsoid for that matter.  <snip>
> Sereno does not use _Ceratops_ as a specifier, but _Ceratops_ is the 
> eponymous genus for Ceratopsoidea, Ceratopsidae, and Ceratopsinae.  It 
> might be best to abandon these names, and replace Ceratopsidae with 
> Centrosauridae.  Sereno suggested replacing Chasmosaurinae with 
> Ceratopsinae back in 1998, but the idea didn't exactly take off (as Sereno 
> [2005] admits), so Ceratopsinae can just be brushed under the carpet, IMHO.

Well, not so fast.  Horn core size isn't necessarily the only character 
which can be evaluated for Ceratops.  Perhaps other skull roof or occipital 
characters can distinguish ceratopsids from more basal taxa, or 
centrosaurines from chasmosaurines.  In fact, Ryan's thesis finds that his 
unpublished taxon is extremely similar with Ceratops and from equivalent 
beds.  I wouldn't be surprised if they were synonymous, though Ceratops' 
holotype is not as obviously diagnostic.

> Salgado (2003) also cites PhyloCode Recommendation 11.8B to support 
> upholding the use of the name Titanosauridae, because _Titanosaurus 
> indicus_ (usually regarded as a nomen dubium) is clearly a member of the 
> clade Titanosauridae, which is diagnosed by procoelous middle caudals.  
> However, there is no guarantee that this character might not turn up in a 
> more basal titanosaurian taxon (or even a non-titanosaurian sauropod - some 
> of which show procoelous proximal caudals).

True, but again we have other characters to consider (e.g. neural arch 
placement).  I don't think anyone doubts Titanosaurus is a titanosaurid (in 
the sense of being more closely related to Saltasaurus than Andesaurus; not 
a phylogenetic definition, but you get the clade I mean).  I'd agree with 
Salgado.  There's nothing in the ICZN saying family names shouldn't be based 
on nomina dubia.

> My point (sorry I didn't get there sooner) is that it is bad policy to name 
> family-level clades after nomina dubia (or even fragmentary taxa).  
> _Ceratops_/Ceratopsinae/Ceratopsidae is a good test case.

To play devil's advocate, both Ceratops and Titanosaurus were very 
distinctive when they were first found.  It's only with hindsight that we 
know strongly procoelous caudals and large brow horns have wide 
distributions.

Mickey Mortimer