Re: phylogenetic position of Achillobator, Yandangornis, etc.

["Mickey Mortimer" <mickey_mortimer@email.msn.com>]

Nick Longrich wrote-

> I keep getting avimimus coming out smack-dab in the middle of the
> oviraptors, near oviraptoridae and  caenagnathids. This is based on:
> beak

This is not really a separate character, but a combined version of toothless
premaxilla and dentary, which are best left separate because of things like
Caudipteryx.

> fusion of premax

The figures of Conchoraptor and Oviraptor in dorsal view in the Dinosauria
seem to show unfused premaxillae.  In the description of Avimimus' skull,
Kurzanov refers to the "premaxillary bones" and "each bone", suggesting
unfused premaxillae.

> fusion of cranial bones
> rodlike jugal bar
> pterygoids closely appressed and fused to base of skull (!!!)

These are also present in birds.

> anterior regions of iliac blades inclined medially

Also present in mononykines, troodontids and ornithomimids.

> propubic pelvis

plesiomorphic

> edentulous premax
> edentulous dentary
> crenellate beak
> dentary medially curved to symphysis to form U-shaped symphysis
> downcurved, pendant paroccipital processes
> elongate retroarticular
> ?long, shallow sliding articular joint for the quadrate
> short pubic boot elongate anterior, short posterior

I agree that these would be good Avimimus+Oviraptorosauria synapomorphies.
They were all included in my analysis.

> Many of the supposedly birdlike features, such as
> -tarsometatarsus
> -large hypapophyses
> -antitrochanter on the ilium
>
> Are actually found in the dromaeosaurs, troodontids, and
> oviraptorids.

What references do you have for tarsometatarsi in these groups?  Also, isn't
the antitrochantor of Avimimus quite a bit larger than the equivalent
structure in these groups?  What about the tall neural canal in dorsal
vertebrae, fused pelvis, unexpanded preacetabular process, reduced pubic
symphysis (~30% or less), ischium less than 70% of pubic length, reduced
obturator process, large posterior trochantor, pedal phalanx II-1 less than
90% of pedal phalanx III-1.  These are all characteristic of paravians or
subgroups of that clade.

Kurzanov's flight-feather attachment point is pretty
> questionable (and kinda moot considering they are in Caudipteryx), and
> there is a carpometacarpus in the type of Oviraptor philoceratops so it's
> kinda questionable what it means to find one in Avimimus...

The ulnar ridge was not considered in my analysis and I have never heard
that the type of Oviraptor has a carpometacarpus- it's merely said to be
closely appressed in Smith (1992?).

Avimimus also
> lacks some of birdlike features seen in paravians, such as the way that
the
> posterior iliac blade comes to a little point, or any sort of
> hyperextension in the toes.

It does taper to a point, but in an odd way.  In "normal" paravians the
(primitively vertical) posterior edge of the postacetabular process slopes
ventrocaudally.  In Avimimus, it seems to not exist or be indistinguishabley
confluent with the horizontal dorsal edge of the ilium.  Ever notice the
Brazilian "oviraptorosaur" is similar in this regard?  I admit, the toes are
weird- but not oviraptorosaur-like either.

> Anyways, I think most of theropod phylogeny is up in the air but
> I'd lay down serious money on this thing being oviraptor if the parts are
> associated, and maybe a couple oviraptor relatives if they aren't from the
> same animal (I think I heard something about some of the vertebrae being
> troodontid though). I just have a measly ~250 character matrix, but I
coded
> pretty much every single 1, 0 and ? from illos in the literature when I
> couldn't from fossil; I tried running the head and postcrania separately
> and got both as oviraptor relatives. My cynical side wonders what this
> proves; I am always disappointed when I don't get what I want out of PAUP,
> and suspicious when I get back what I thought I should.

It very well may be an oviraptorosaur- we'll just have to wait and see what
the Mesozoic bird volume says.

> I think you likely got Protarchaeopteryx dead-on, tho, though we
> desperately need better fossils of that animal to prove this. Those
> super-long caudal transverse processes, e.g. are classic oviraptorosaur.

Transverse processes, eh?  Never noticed that.  If not better fossils, at
least a better description, with lots of illustrations is needed.  I wish I
would have taken more advantage of seeing it first hand...

Mickey Mortimer