RE: Defining Ornithischia (was Re:)

[Tim Williams <twilliams_alpha@hotmail.com>]

Guy Leahy wrote:

> Some authors would further expand/subdivide Ornithischia.

When you say "some authors", do you mean "one author"?

> For example, in two issues of the popular magazine Prehistoric Times 
> (Issues # 80 and # 81:
>
> http://www.prehistorictimes.com/backissue.html
>
> David Peters has written articles where he groups *Lotosaurus*, *Effigia*, 
> *Sacisaurus* and *Silesaurus*together as a subclade within Ornithischia.  
> Mr. Peters coins the term "Paraornithischia"
> for this subclade.  Mr. Peters defines "Paraornithischia" as ornithischians 
> which possess a predentary bone, but do not have retroverted pubes.

Oh dear.

With all due respect to David Peters... this is rubbish.  OK, so I guess I'm 
stretching the obligatory "with all due respect" to breaking point, but here 
goes...

First of all, it is very difficult to take Mr Peters' phylogenies seriously, 
given his (a) lack of understanding of cladistic methodology in general; (b) 
lack of understanding of character coding in particular; (c) use of 
imaginary characters obtained by Adobe Photoshop.  Give a computer with PAUP 
to a tree full of monkeys and they would probably produce the same phylogeny 
as Mr Peters.

Secondly, it sounds like Mr Peters is using a character-based definition for 
Paraornithischia.  However, from your description of "Paraornithischia" it 
appears that this group is paraphyletic, and therefore not a clade.  I'm not 
certain that Mr Peters is aware of the difference.

Thirdly, I would not look to "Prehistoric Times" for the latest 
ornithischian phylogeny.  I would defer to the scientific literature, 
preferably peer-reviewed.

This is not a criticism of Guy Leahy (it was an honest and well-intentioned 
posting) or of Prehistoric Times.  It's merely an attempt on my part to 
bring ornithischian phylogeny back to reality.

Cheers

Tim

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