[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

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



(apologies for cross-posting)

On 10/10/05, Tim Williams <twilliams_alpha@hotmail.com> wrote:
>
> 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.

This is a very good point. But I think there is also some kind of
responsibility with converted names to accord with historical usage.
For example, _Maniraptora_ was initially defined as a stem-based clade
specified internally by _Aves_ (sensu stricto) and externally by
_Ornithomimus_, and that's all it has ever meant. Nobody wants to
change the definition if certain taxa, like _Tyrannosauroidea_ or
_Therizinosauria_, fall inside or out under various topologies,
because it's intrinsically understood as a stem-based clade.

With taxa like _Ornithopoda_, though, there are decades of usage
before it was ever given a phylogenetic definition. Much more care
must be taken with the definition. Then there are taxa like
_Euornithopoda_, not converted from traditional taxa, but named after
them--a blurry area in between.

Then again, some taxa, like _Dinosauria_ and _Archosauria_, have been
embraced as defined clades, so maybe it's just a matter of overturning
everybody's preconceptions, one taxon at a time.

Good luck...
--
Mike Keesey
The Dinosauricon: http://dino.lm.com
Parry & Carney: http://parryandcarney.com