Re: Coelurosaur phylogeny

["Mickey Mortimer" <Mickey_Mortimer111@msn.com>]

Thomas Holtz wrote-

> > While I agree it is preferrable to have a written definition for a clade
> > (diagnoses are comparatively useless due to their lack of stability),
it's
> > not an official rule that this must occur before a clade name is used.
I
> > fail to see the difference between indication of content in a
> > figure versus
> > in text.  Surely one is as good as the other.
>
> Not as such.  Specifically, a label on a figure does not state the
> definition, but leaves open several different alternatives.  It does not
> specify if that name is node-based, stem-based, apomorphy-based, or
> content-based.  It does not specify the anchor taxa or "anchor characters"
> or required content.

Oh yes, I agree a written definition is far more useful than a figure label
(and should be necessary for a valid clade name once Phylocode is
implemented).  I was just saying a written "indication of content" (eg. "We
introduce the name Enigmosauria for the clade containing oviraptorosaurs and
segnosaurs") is no different than a node labeled Enigmosauria on a
cladogram.  Jaime seemed to have a problem with content being indicated by a
figure as opposed to text, as he wrote- "The point of my post was to point
out the use of a name used in a _figure_ as being anything applicable to any
clade, when there is no statement accompanying that defines its useage,
either a diagnosis, indication of content, or definition."

> But such differences ARE imperative, as the stem-based and node-based taxa
> are different taxa with different ancestors.  Okay, they KNOWN membership
> might be the same, but the goal of phylogenetic taxonomy (itself a more
> inclusive term than just the PhyloCode: I know of many PT practitioners
who
> are not pleased with various aspects of the PhyloCode, and dread it as the
> potential downfall of PT) is a phylogeny based on statements of ancestry.
> As such, a stem-based and node-based name are necessarily different taxa,
as
> they have different ancestors.

True, but it's not imperative for discussion at this point, though it will
be in the long run.  My point was that the "stem enigmosaurs" are so poorly
known at this time that you'll be discussing almost the same clade whether
using a node- or stem-based definition.  It's not like dromaeosaurids, where
lots of well known taxa (eg. Microraptor, Bambiraptor, Sinornithosaurus)
could be included or excluded depending on which definition you apply.  Not
that we should be content with Enigmosauria being so poorly defined, but we
can live with it for now.

> Futhermore, without a text statement of definition, how would we know what
> happens to "Enigmosauria" when (for a hypothetical example) it turns out
> that oviraptorosaurs are closer to eumaniraptorans than to
> therizinosauroids?  If it is a node-based name anchored on _Oviraptor_ and
> _Therizinosaurus_ (for examples) then Enigmosauria also includes
> Eumaniraptora; if it is a stem-based name anchored on _Oviraptor_ (say
"all
> taxa closer to _Ovi._ than to _Passer_") then it excludes
therizinosauroids
> in this topology; if anchored on _Therizinosaurus_ then it excludes
> oviraptorosaurs.

This is a problem of course, but it would still exist if there was a written
diagnosis or "indication of content".  Only when phylogenetic nomenclature
comes in does this get solved.
I was never arguing figures could or should be used to define clades, or
that clades shouldn't have explicit definitions.  I was just saying a
cladogram is just as effective as a written indication of content for
defining a clade (both doing pretty bad jobs of it), and that no published
clade names (above the family-grade level covered by ICZN) are invalid or
unofficial until Phylocode is implemented.

Mickey Mortimer