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Re:



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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