Re: Coelurosaur Phylogeny

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

George Olshevsky (dingogeorge@aol.comn) wrote:

<Segnosauria was defined by listing its contents way back in the early
1980s  (was it Barsbold's 1983 dissertation? I think so). This is good
enough to  establish the name. ICZN does not rule on taxa above family
level, so it will  be usage that ultimately determines whether or not
Segnosauria is accepted.  Therizinosauria is a latecomer name and I prefer
Segnosauria, having used it  with some frequency for the past 20-odd
years.>

  The ICZN cannot dictate how either name in preference would be used, so
the nature of synonymy is not enforceable (nor is it recommended, a case
can be made, based on current systematics, for using _both_ names for
different clades). Barsbold's usages (not definitons) of the name
Segnosauria was confined to what we would now use as a subset of
therizinosaurids, as it included only the therizinosaurids *Segnosaurus*,
*Erlikosaurus*, and *Enigmosaurus*, based and diagnosed by pelvic
features. The other therizinosaurids that lack these features, if one
wanted to use the included taxa (as Enigmosauridae and Segnosauridae) such
as the "nanshiungosaurid" (Dong still used this in Dong and You, 1995,
describing *Nanshiungosaurus bohlini*) *N. brevispinus* would be a
non-segnosaurian therizinosaurid. This is problematic as Barsbold,
Maryanska, & Osmolska, 1990 (_The Dinosauria_) used Segnosauria and
included the same taxa, as well as *Therizinosaurus*; Maryanska used both
taxon names (Therizinosauria was included by implication with
"therizinosaurs" as used, but so was "segnosaurs") but preferred
Segnosauria (it came first and was not in parentheses, as was
"therizinosaurs") in 1997 in Farlow and Brett-Surman's _Complete
Dinosaur_, and included *Therizinosaurus* as well as *Alxasaurus*; whereas
in the later volume (by a month, I beleive) Russell (1997) independantly
used the name Therizinosauria for the same taxa. This was defined by
Russell at that time.

  None of this, priority of issues, is relevant since in any case, the
ICZN does not commend use of Therizinosauria, or Segnosauria, and
phylogenetic taxonomy is not sound until or if the PhyloCode is ever
enforced, and then it will be like the ICZN ... you can follow or not. So
even if one taxon is used more, both may be valid, except that a
definition does not render the application of another prevalent name
invalid. Russell should have known this as he was the only worker
preferring "Therzinosauria" in the first place and ignored all other uses
of Segnosauria in mainstream works on the group. However, Mike Keesey is
right and if you prefer PT and wish to follow the PhyloCode draft, then
Therizinosauria is the only one that can be used until Segnosauria is
explicitly defined. Problem is, Russell's definition is essentially one of
the longest in dinosaur works, given that it specifies all included
therizinosauroids (by name) and excludes particular groups, rather than
species. This definition should be condenses, if you want to conform to
PhyloCode's draft recommendations.

  Cheers,


=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

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

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