Re: Coelurosaur ischium unique?

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

Nick Pharris (NJPharris@aol.com) wrote:

<Tyrannosaurs and ornithomimosaurs generally have ischia more than 2/3 the 
length of the pubis,
and at least some specimens of each have obturator processes placed less than 
25% down the ischial
shaft.>

  Mononykes and birds also have ischia longer than 2/3 the length of the pubis, 
and for this
apparent nesting indicates they reversed the plesiomorphic condition (relative 
to them) of short
ischia. This is not regarding Sereno's usage of Ornithomimoidea, which can be 
considered a
relative sistergroup relationship. However, Sereno's usage is thus:

--Ornithomimoidea
   |--Ornithomimidae
   `--Alvarezsauridae

  He apparently sunk Ornithomimosauria into Ornithomimidae as effective 
synonyms by defining
Ornithomimidae as *Pelecanimimus* + *Ornithomimus*. Effective use of a 
perfectly good taxon
(Ornithomimosauria) was dissolved by making it a heterodefinitional synonym of 
Ornithomimidae.
This may have been done as an attempt to establish a traditional -oidea, -idae 
nesting
relationship. Mononykine elongated ischia in this scheme, however, is no longer 
such a distinct
reversal as the ischia of ornithomimes are also elongate. However, all other 
analyses besides
Martin's and Sereno's (Holtz, 2000, 2001; Chiappe, 1996; Novas, 1996; Chiappe 
et al., 1998)
indicate that mononykes are closer to birds than are ornithomimes or they are 
to ornithomimes, and
that Ornithomimoidea is a heterodefinitional synonym of Maniraptoriformes. 
Who'da thunk?

<Coelophysoids can't really be said to have obturator processes at all. I am 
pretty sure I have
never seen a non-coelurosaur with the classic, _Ornitholestes_- or 
_Deinonychus_-type triangular
obturator process.>

  Actually, considering the recent publication of Currie and Chen, 2001, on 
*Sinosauropteryx*,
there is in fact a "trapezoidal" obturator process, with a distinct 
ventrocaudal notch in the
process that gives the element a distinctive allosaurine appearance. 
*Compsognathus* does not have
this condition (Bidar et al.; Ostrom, etc....).

=====
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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