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RE: Defining Ornithischia (was Re:)



--- Tim Williams <twilliams_alpha@hotmail.com> wrote:

> Guy Leahy wrote:
> 
> >Some authors would further expand/subdivide
> Ornithischia.
> 
> When you say "some authors", do you mean "one
> author"?

Yes... 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.

I would agree... :-)

> 
> 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.

Mr. Peters is using a character-based definition for
Paranornithischia.  For example, Mr. Peters regards
the following characters as important in establishing
a relationship between Lotosaurus, Silesaurus and
Lesothosaurus:

1. Ventral maxilla is narrow.
2. The orbit marks the halfway point of the skull.
3. The quadrate rises vertically and is concave
posteriorly.

Mr. Peters inteprets Effigia and Lotosaurus as 
possessing a predentary bone, along with Silesaurus
and Sacisaurus. Mr. Peters provides a alternative
restoration/interpretation of the Effigia skull using
his tracing technique.  Mr. Peters also discounts the
presence of a calcaneal spur in Lotosaurus and Effigia
as a character that would disqualify these taxa as
ornthischians.

David Peters does not restrict his thoughts regarding
alternative phylogenies in the Prehistoric Times
articles to ornithischians.  In issue # 80, Mr. Peters
gives us his interpretation of all of Amniota.
He states that he used 151+ taxa with 228 characters,
the matrix for which he created in MacClade and
analyzed with PAUP.

A few of the conclusions from David Peter's effort
are:

1. Cephalerpeton is considered to be the basalmost
amniote.
2. Tetraceratops is removed from Synapsida, and its
sister taxa is Limnoscelis, with Tseajaia as the next
outgroup.
3. Diadectes is considered as an amniote, with
Procolophon the nearest outgroup.
4. Sharovipteryx is the nearest sister taxa to
pterosaurs, with Saltopus the next outgroup.
5. Lagerpeton and Tropidosuchus are sister taxa, with
Teraterpeton and Chanaresuchus the next outgroups. Mr.
Peters also groups one specimen of Youngina as a
sister taxon with Chanaresuchus.  
6. Marasuchus and Herrerasaurus are sister taxa, with
Thecodontosaurus the next outgroup.
7. Silesaurus and Lotosaurus are sister taxa within
Ornithischia, with Pisanosaurus the next outgroup.
8. Scleromochlus is nested within Crocodylomorpha,
between Gracilisuchus and Pseudhesperosuchus.

> 
> 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.

No criticism taken... ;-)  

> 
> Cheers
> 
> Tim
> 
>
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