AVIMIMUS

[Tetanurae <Tetanurae@aol.com>]

There has been much talk on this list lately about the idea that _Avimimus_
may be a chimera.  This idea I think has quite (QUITE) a lot of merit.  First
of all, as George has pointed out, the holotype is just the skull cap, which
is good.  I would rather not have to go through a painful disection of the
holotype and have that damn carpometacarpus become the holotype....

Because the refered material has some very strong similarities with
mononykines and oviraptorids, I once considered them as sister groups, or
mononykines as the sister group to elmisaurs within the oviraptorosauria...  I
have since come to the conclusion that this thing is more likely a chimera
since it is only the head that is similar to oviraptorids and only the feet
that are similar to mononykines, and there are elements that could easily
belong to different animals entirely and don't really much resemble oviraptors
or mononykines.

SKULL

>From what is preserved of the skull cap and the rostrum, it is clearly an
oviraptorosaur.  I am not too sure of Perle's suggestion that it is a baby
oviraptorid, it could be I suppose, but it could also belong to an adult of a
different taxon (Avimimus).

The skull is oviraptorosaur* because:
1) the upper and lower jaws are toothless
2) the premaxilla sports krenulations
3) the rostrum fragment has a depression previously called the external nares,
but is probably the anteorbital fossa because it has an extra hole (maxilary
fenestra) in it: so the dorsal migration of the nares over the AOF
4) long, slender jugal

It is becoming quite clear that previous reconstructions  of _Avimimus_ are
quite wrong (Kurzanov, Paul, Chaterjee) in light of the fact that the
rostrum's depression is probably the AOF.  All three authors have illustrated
the postorbital-jugal bar as being gone, but since both elements are broken it
is not known.  I would suspect that it is still there.

FEET

It is becoming clear now that there are three basic types of arctometatarsaly:
Elmisaur arctomet pedes are arctomet on the dorsal surface, but not at all
arctomet  on the plantar surface.  True arctomet pedes (tyrannosaurs and
bullatosaurs) are arctomet on the dorsal surface, and somewhat arctomet on the
plantar surface (MT III is pinched, but the proximal portion is not obscured).
Mononykine arctomet pedes are fully arctomet on both dorsal and plantar
surfaces.

The feet refered to _Avimimus_ are clearly of the last type.  No other
theropods have feet that aproach this condition so it is either indicative of
a clse relationship between oviraptors and mononykines (unlikely as per
discussion the past week or so), a case of tremendous convergence (unlikely),
or indicative of the fact that this is actually a chimera.

OTHER ELEMENTS

I don't know who owns the skeleton that goes between the head and the feet...
The tibiae seem to bear some resemblance to _Oviraptor_, the pelvis could have
come from an Oviraptorosaur, or even something like _Bagaraatan_....  Anyone
want to give me a grant to fly to Moscow?

Peter Buchholz
Tetanurae@aol.com

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*I will refrain from refering to skulls as oviraptorid or oviraptorosaur
because, even though Sues has added new data, it is still inclear what a
caenignathid/elmisaurid skull looks like.