RE: Stegosaur volume of Swiss Journal of Geosciences

[Tim Williams <tijawi@yahoo.com>]

On Sat, 18/9/10, Anthony Docimo <keenir@hotmail.com> wrote:


> > But how do we know that Ceratopsidae encompasses _Ceratops_?
>
>  just a hunch....because that's how it was created in the first place?


Well, you'd be forgiven for thinking that.  But many things have changed since 
Marsh (1888) first came up with the family Ceratopsidae.  We now use 
phylogenetic taxonomy, which has unsettled certain time-honored assumptions.


Currently, every phylogenetic definition that has been proposed for 
Ceratopsidae has pointedly excluded _Ceratops_, the name-giving taxon.  
Instead, these definitions have included well-known genera such as 
_Triceratops_  and _Centrosaurus_ (Dodson et al., 2004; Sereno, 2005), or 
_Triceratops_ and _Pachyrhinosaurus_ (Sereno, 1998).


So if Ceratopsidae is defined as the least inclusive clade that includes 
_Triceratops_ and _Centrosaurus_ (Sereno, 2005), then in order for _Ceratops_ 
to be a ceratopsid, it has to be shown to be a member of this clade.  This can 
only be done by phylogenetic analysis.  Until this is demonstrated, it remains 
an open question whether _Ceratops_ is a ceratopsid.


> then shouldn't our default assumption (at least until proven otherwise) 
> be that _Ceratopsidae_ counts _Ceratops_ as a member?


No; we shouldn't be *assuming* anything.  We should be hypothesizing, then 
testing.  The hypothesis is that _Ceratops_ is a member of the least inclusive 
clade (Ceratopsidae) that includes _Triceratops_ and _Centrosaurus_.  Until 
this hypothesis is tested, it should not be simply assumed that _Ceratops_ is a 
ceratopsid.  


Both the ICZN Code and the draft PhyloCode actually require that _Ceratops_ (as 
the name-giving genus) is a member of Ceratopsidae.  Thus, we should either 
include _Ceratops_ in the definition of Ceratopsidae; or we should scrap the 
name Ceratopsidae for this clade. 



Cheers

Tim