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

[Tim Williams <twilliams_alpha@hotmail.com>]

Mike Keesey wrote:

> Since _Euornithopoda_ is defined as clade(_Parasaurolophus_ not
> _Heterodontosaurus_), Butler's findings would render marginocephalians
> and possibly thyreophorans as euornithopods(!)

Certainly marginocephalians would be euornithopods, going by Fig. 26.  If 
Ornithopoda is defined as a node-based clade anchored on _Heterodontosaurus_ 
and _Parasaurolophus_ (Sereno, 1998), then marginocephalians are both 
ornithopods and euornithopods.

But if the stem-based definition of Ornithopoda is used ("all cerapodans 
closer to _Edmontosaurus_ than to _Triceratops_"), then marginocephalians 
cannot be ornithopods, and Ornithopoda becomes a clade *within* 
Euornithopoda!  Oh dear...

> But this is probably about as far as the discussion can go until
> further studies are done.

The point I'm driving at is that there is always going to be "further 
studies".  These studies are destined to overturn previous topologies, with 
the result that many current PT definitions are tossed around like corks in 
the ocean.  Many clades are defined with a specific topology in mind, 
without considering the possibility that future analyses may recover a very 
different topology.  Until we have the One True Tree, then taxa are going to 
move around with each new analysis, and definitions should take this 
account.

Sorry... this message took on a life of its own and somehow turned into a 
rant.

Cheers

Tim