Re: Shuvuuia

[Mickey Mortimer <Mickey_Mortimer111@msn.com>]

Jaime Headden wrote-

> Mark Van Tomme (markvantomme@yahoo.com) wrote:
>
> <It seems that that skull is actually a troodontid one on the progress of
> description and will be published in a AMNH bulletin with some other
> troodontids,including some chinese ones that are part of the clade.>
>
>   The skull in question is currently on display near the block of an
> undescribed troodontid skeleton from Ukhaa Tolgod. This skull has white
> bone and reddish/brown matrix, so likely derives from the Djadokhta-type
> beds. There are several morphological features, however, that indicate
> that it IS an alvarezsaur, including absence of an ascending process of
> the jugal, a feature of the "prefrontal/lachrymal" that projects into the
> orbit, extremely minute and high-crowned teeth, no "crowding" of teeth at
> the rostral end of the jaw (they all appear to be evenly distributed along
> the jaw), no lateral dentary groove for the dental nutrient foramina, and
> a strongly curved posterior margin of the quadrate, which all occur in
> *Shuvuuia.* These features make it likely that this skull IS an
> alvarezsaurid.

I agree with most of these characters, barring the dorsal jugal process,
whose base is visible on the left side.  I don't feel the anterior crowding
or lateral dentary groove are unambiguous enough in the photo to make a
judgement on yet.  There are some other characters it has which are unlike
troodontids.  The nasals are short compared to the frontals (unlike Shuvuuia
too).  The jugal is very low compared to orbital height (like Shuvuuia).
The splenial isn't broadly exposed laterally (like Shuvuuia).  The
retroarticular process is elongate (also like Shuvuuia).  However, there are
several ways in which it resembles troodontids more than Shuvuuia.  The
maxillary teeth cover over 30% of the maxilla, unlike Shuvuuia and
Pelecanimimus.  The lacrimal has an elongate posterior process, making it
'T-shaped'.  The prefrontal appears to be absent.  The outline of the
supratemporal fossa on the frontal is sinusoidal, a deinonychosaurian
synapomorphy.  A sagittal crest on the parietal appears to be present.  The
quadrate is angled posteriorly a significant amount (>5 degrees).  The
foramen magnum is taller than wide.  The pes is quite obviously troodontid,
and the forelimb is different from the derived morphology in alvarezsaurids.
The forelimb resembles other troodontids except for the elongate phalanx
II-2 and subequal III-1 and III-2.
I added the taxon to my analysis, and it ended up as a basal troodontid,
more primitive than Sinovenator, IGM 100/44 or Sinusonasus.
Archaeornithoides (from the same formation) was the next outgroup.

Mickey Mortimer