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




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