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Re: ARCHAEORNITHOMIMUS



Dwight Stewart wrote:

<Originally, I had read that this Chinese dinosaur may have been the
oldest ornithomimid or ostrich mimic dinosaur. But recently an
acquaintance of mine said that the small 4th finger on the manus has
brought this into question. I believe that the 3rd digit is the
shorter one (but am not certain). My question is this: if 5 or 4
digits is generally a more primitive state, why would the presence of
a shorter (& then, therefore PERHAPS atrophied) digit in an earlier
Specimen of potential ornithomimid disqualify it from being an an
ostrich mimic? Am I missing something here or is the specimen too
incomplete to tell?>

  First, Ornithomimosauria is *Pelecanimumus* (Perez-Moreno et al.
1994) and Ornithomimoidea; Ornithomimoidea is *Garudamimus* (Barsbold,
1981) and Ornithomimidae; Ornithomimidae has everyone else:
*Archaeornithomimus*, *Gallimimus*, and the
*Ornithomimus*--*Struthiomimus*--*Dromeciomimus* group, in
increasingly advanced steps (regard the three-taxa group above as one
step: it's hardly a resolved taxonomic tangle, as Greg Paul and others
have demonstrated). And *Deinocheirus* most probably falls somewhere
in there.

-------

  I can tell you that the manus of *Archaeornithomimus* is by no means
primitive, having a well-developed, elongate metacarpal I that is
fully appressed to metacarpal II along its entire length, though mcI
does not reach the end of mcII or mcIII. This is certainly more than
can be said for *Harpymimus*, barring its consideration as a basal
therizinosauroid, as Peter Buchholz has suggested.

  There is a more primitve ornithomimosaurian dinosaur,
*Pelecanimimus*, whose manus has mcI as long as mcIII and almost as
long as mcII and is more advancedly appressed along all elements, plus
has fully discoidal distal carpals, like its more famous cousins,
*Ornithomimus* and *Gallimimus*, which does suggest that these
features, found only in Ornithomimosauria, are advanced and
synapomorphic of the whole group.

  *Archaeornithomimus*, though I know of no data on carpals (certainly
not in Smith and Galton, 1990), possesses an apparent reversal, where
the metacarpals are all subequal in length, and mcIII is much thinner
than the rest and does not appress mcII along its length; however, the
hand mentioned comes from the type, which is a juvenile, so these may
be ontogenetic and only exist in pre-adult forms. Juvenile North
American ornithomimids and *Gallimimus* are known, and I haven't seen
the data there.

  Also, there is no data on whether any specimen of Ornithomimosauria
has a fourth (or even fifth) metacarpal. No coelurosaurian, or
avetheropod, has, to my knowledge, a fourth (much less a fifth)
metacarpal.

==
Jaime A. Headden

Qilong, the website, at:
http://members.tripod.com/~Qilong/qilong.html
---
All comments and criticisms are welcome!

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