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Defining Ornithischia (was Re:)



Some authors would further expand/subdivide
Ornithischia.  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.

Guy Leahy


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

> Nick Gardner wrote:
> 
> >And as usual, no one really seems to give a damn
> about Ornithischia,
> 
> Hey I do!
> 
> >A very basic model of the current understanding of
> Ornithischian
> >groups would probably be something like the
> following:
> >
> >Heterodontosauridae
> >Stegosauria
> >Ankylosauria (your "armored dinosaurs")
> >Ornithopoda (this would include your "duckbilled
> dinosaurs" and
> >"iguanodons", as well as lots of other taxa which
> are serially closer
> >to them)
> >Pachycephalosauria (this would be your "boneheaded
> dinosaurs")
> >Ceratopsia (this would be your "horned dinosaurs")
> >
> >Of course, this doesn't take into account forms
> that do not fall into
> >these groups, like basal thyreophorans (such as
> Scutellosaurus) and
> >basal ornithischians like Pisanosaurus or
> Lesothosaurus.
> 
> And now _Eocursor_.
> 
> According to one recent phylogeny, the "basal
> ornithischian" category may be 
> even broader.  Many taxa that used to be regarded as
> "hypsilophodont-grade" 
> ornithopods (but not _Hypsilophodon_ itself) might
> in fact be basal 
> ornithischians, as non-cerapodan neornithischians.
> 
> To complicate things even further (and I know this
> is not news to Nick), the 
> heterodontosaurids could be basal ornithischians,
> basal cerapods, basal 
> ornithopods, or basal marginocephalians (or
> heterodontosauriforms).  They're 
> a weird bunch.
> 
> >It's important to understand that most researchers
> don't just split
> >groups into the old Linnean ranks anymore,
> 
> Praise the Lord for that.
> 
> Cheers
> 
> Tim
> 
>
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