Re: Stormbergia dangershoeki, new Early Jurassic ornithischian from South Africa

[Tim Williams <twilliams_alpha@hotmail.com>]

T. Michael Keesey

> > ... and ceratopsians and pachycephalosaurs as derived ornithopods.  At
> > least, that's how I read Butler's tree.
>
> Depends on which definition of _Ornithopoda_ you are following. Sereno 
> (1997) considered it a node-based clade, and anchored it on 
> _Heterodontosaurus_ and _Parasaurolophus_ (1998), but in the latest edition 
> of The Dinosauria, it is "all cerapodans closer to _Edmontosaurus_ than to
> _Triceratops_", which explicitly excludes _Marginocephalia_.

Using Butler's tree, these two definitions give an Ornithopoda that are very 
different in content.

> "Classic" Ornithopoda is a massively paraphyletic assemblage roughly 
> equivalent to "unarmored
> _Ornithischia_" or "bipedal _Ornithischia_". In adapting it to cladistic 
> taxonomy, there seems to be a consistent desire to restrict it to a 
> particular lineage (a la _Amphibia_) rather than expand it to include 
> descendants (a la _Dinosauria_), probably because the very popular term 
> "Ornithischia" is already available for the expanded group (not to mention 
> "Predentata").

Yes, the traditional/classical Ornithopoda also included scelidosaurs, 
psittacosaurs and pachycephalosaurs.  So I can't see why Ornithopoda 
shouldn't be node-based and expanded to include pachies and ceratopsians, 
should the topology show that iguanodontians and marginocephalians are 
closer than previously thought.

Cheers

Tim