Re: Ornithopoda + (Heterodontosauridae + Marginocephalia) phylogeny

["T. Michael Keesey" <mightyodinn@yahoo.com>]

--- Tim Williams <twilliams_alpha@hotmail.com> wrote:
> Tom Holtz wrote:
> 
> However, I don't know how Ornithopoda is defined - is it stem-based or 
> node-based, and if node-based is _Heterodontosaurus_  one of the anchor 
> taxa?  If it is, and Heterodontosauridae and Marginocephalia form a clade, 
> then pachies and ceratopsians would all become ornithopods.  Looks like 
> another job for Mike...   :-)

No problem.

Sereno 1998 defined it as Clade(_Heterodontosaurus_ + _Parasaurolophus_). I'm
not aware of any other formal definitions in the literature. (_Euornithopoda_
was defined as Clade(_Parasaurolophus_ <- _Heterodontosaurus_) in the same
paper.)

So, yes, under this definition, _Ornithopoda_ could include pachycephalosaurs
(not so objectionable), psittacosaurids (somewhat objectionable, but it's been
done before), and neoceratopsians (pretty objectionable). Personally, I feel
these definitions should be revised. A stem-based _Ornithopoda_ and a
node-based _Euornithopoda_ would be very useful.

Incidentally, I don't have the paper, but I *think* it may have defined
_Heterodontosauridae_ as Clade(_Heterodontosaurus_ <- _Parasaurolophus_), which
could also include pachies and ceratopsians. I could be wrong, though.


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