Re: A critique of Sullivan's pachycephalosaur paper,

["Jaime A. Headden" <qilongia@yahoo.com>]

Mickey Mortimer (mickey_mortimer111@msn.com) wrote:

<<Sullivan's diagnosis for Pachycephalosauridae reads like one of those classic
'diagnoses' from the 1950's that lists symplesiomorphic or variable characters
in addition to synapomorphies.  "Ornithischian dinosaurs with thickened,
fully-flat or incipiently to fully-domed frontoparietals."  So... the
thickening is all that needs to be mentioned then.  "Supratemporal fenestrae
absent to well-developed."  Uh... this would exclude which states now?>>

David Marjanovic (david.marjanovic@gmx.at) wrote:

<This is apparently not _intended_ to be a diagnosis (or "definition"). It is a
description, at best a determination key. "If you see an animal that fits this
description, it probably is a pachycephalosaurid.">

  Sullivan's diagnosis is the classic form of diagnosis, by which features are
listed that are present in the group that can be recognized in most if not all
the taxa. It is not meant to be differential, or really, even descriptive. It's
a MASSIVE summary of the most extreme differences. Unfortunately, it means any
ornithischian with a thickened braincase falls into this as the statements are
so general as to be worthless. For example, ankylosaurs perfectly fall into the
diagnosis by Sullivan's reckonning. This differs significantly from Sullivan's
2003 treatment of the group in which diagnoses were "characters present" in the
more phylogenetic sense. This is probably what Mickey is referring to.

  Cheers,

Jaime A. Headden
http://bitestuff.blogspot.com/

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)

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