Re: Pygostylia and Oviraptorosauria

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

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

<I'd also like to know if there's any published version of the commonly
used stem-based non-definition of Oviraptorosauria which includes
*Microvenator*, *Nomingia*, *Caudipteryx* and probably
*Protarchaeopteryx*, considering that the official definition is
{*Oviraptor* + *Chirostenotes*} Sues, 1997 -- why has this clade got the
name Caenagnathoidea, and when? --, and that the only other definition I
can find in the literature is {*Oviraptor* > Neornithes} Sereno, 1998.>

  Only two definitions for Oviraptorosauria have been published.
Barsbold's original usage was differentiate, among toothless theropods,
*Oviraptor* and *Ingenia* from ornithomimids; at the same time, he named
Ornithomimosauria, and included two "families", Garudimimidae and
Ornithomimidae. Barsbold suggested Caenagnathidae was a grouop of
oviraptorosaur-like animals, but they were not included until much later.
Sereno used the definition {Oviraptor + Chirostenotes} for "Oviraptoridae"
in 1999, and then changed the name, in accordance to the ICZN (art. ?) to
Caenagnathoidea to comply with the oldest included family-name,
Caenagnathidae (1940) [compare to Oviraptoridae, Barsbold, 1979].

  Other definitions have been offered, for instance a series of contents
to include several basal forms that have only recently (as of 1998 or
later) been considered as oviraptorosaurs. One publish phylogeny includes
*Protarchaeopteryx* as a possible oviraptorosaur, but only Mortimer
(unpublished) has tried to explicitly test this. However, none of these
holds serious weight, and none have been explicitly discovered to be very
robust. Some are quite plesiomorphic.

  Definitions are:

  Barsbold, 1979a, b "*Oviraptor* <- *Ornithomimus*", as implied by
taxonomy and phylogeny
  Sues, 1997 {*Oviraptor* + *Chirostenotes*}
  Sereno, 1999 [sensu 2000] {*Oviraptor* <- Aves}

  Holtz' formulations in 1995 and more recent have supported the use of
*Ornithomimus* as the common stem in maniraptoriform and maniraptoran
definitions and thus included groups. Sereno used Sues' definition for
Caenagnathoidea, hence the group is a homodefinitional synonym of
Oviraptorosauria, if one applies priorities to definitions (I favor this
treatment, though the rule is not enforceable for the present, but would
prefer both taxa have different definitions that both be preserved). I
also favor Barsbold's original treatment of the group, as it preserves the
same information, and still permits the possible treatment of
therizinosaurs as the closest outgroup. Other names may be required to
define other included forms. However, in any definitional usage,
therizinosaurs as the closest outgroup to oviraptorosaurs proper, will be
called Oviraptorosauria to include both groups. This is not under the
original intent since all treatments of the taxa in question that have
found the sister group relationship, they have been mutually exclusive,
and a clause may be formulated when formal definitions are adopted, to
define Oviraptorosauria as {*Oviraptor* <- *Ornithomimus*, Aves, or
*Therizinosaurus*} which should please many people. *Velociraptor* and
*Troodon* (or a suitable taxon that can actually be well-compared) may be
added to further define the stem. A node-based clade to include segnosaurs
and oviraptorosaurs, and a stem opposing oviraptorosaurs to include
segnosaurs may be required. I have posted on this in the past.

=====
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.

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