Re: Shuvuuia

[Mickey Mortimer <Mickey_Mortimer111@msn.com>]

Jaime Headden wrote-

> The skull also
> has features of the orbit (extremely tall and elongate: over 1/4 skull
> length and almost as high as long) and relatively large braincase to snout
> length that suggest, contra either troodontids or described skulls of
> *Shuvuuia,* that it may be juvenile.

Or, this could be natural for a basal troodontid, as birds have short snouts
as well.

> There is a very large antorbital fenestra, with what
> seems to be a tiny premaxillary fenestra almost enclosed by the anterior
> rim of the antorbital fossa, unlike troodontids except for *Sinovenator,*
> and it IS found in *Shuvuuia.*

Chiappe et al. (2002) state the presence of a promaxillary fenestra in
Shuvuuia is uncertain.

> The quadrate is more anteriorly inclined by
> nearly 1/4 the length of the quadrate, something resembling *Shuvuuia,*
> and not at all caudally inclined.

The proximal condyle is posterior to the distal condyles, with the quadrate
angled about 35 degrees to the ventral skull margin, which is more than the
near right angle seen in Shuvuuia, but developed (albeit more poorly) in
Saurornithoides and Troodon.

> The extreme small size of posterior
> maxillary teeth is at odds with EVERY troodontid, as this specimen lacks
> any apparent size gradation along the jaw for teeth, but this is not too
> important: basal troodontid teeth are virtually indistinguishable from
> alvarezsaur teeth apart from relative size.

If it's a basal troodontid, this may not matter much.

> There is an elongate, tapering
> process of the retroarticular; the post-dentary bones are incredibly
> shallow; the post-dentary bones become shallower caudally until they taper
> into the retroarticular process -- all unlike troodontids.

Postdentary bones are very shallow in IGM 100/44.  I agree regarding the
posterior taper, and already mentioned the retroarticular process.

> The dentary is
> gently curved upwards and it would appear gently _inwards_.

Medial curvature is indeterminate.  Upward curvature is more in agreement
with Sinovenator and Byronosaurus than the slightly ventrally curved dentary
of Shuvuuia.

>   Contra Mickey, the base of the ascending ramus of the jugal is not
> apparent, though the jugal does get deeper caudally (this is true in
> *Shuvuuia* as well).

Well people, check out the skull here-
http://paleo.amnh.org/gobi/onload.html and make your own decision.
The skull is labeled as Shuvuuia, and is under "Fossil Discoveries".

> The foramen magnum hardly appears to be complete, as
> it's angle from the photo taken gives it both a quadrangular aspect, and
> the look of erosional defects that suggests it is not as complete as it
> could be, especially in regards to the supraoccipital and left
> exoccipital.

We'll have to wait for better pics to determine which of us is right.

> I have no idea what Mickey is talking about when he refers to
> a sagittal keel on the parietals, as the fossa that converge medially
> appear to leave a platform, rather than a compressed keel; but, that is
> fine: a keel is absent in some skulls attributed to *Troodon* as well.

I don't see a platform.  Examine the right posterolateral view.

> The
> presence of a T-shaped lachrymal is largely pointless: it has long been
> held that the prefrontal had been incorporated into the troodontid
> lachrymal, as in other taxa, and the separate prefrontal/preorbital
> ossification in *Shuvuuia* can easily be accounted as part of the
> prefrontal-lachrymal complex.

Seems not to be how the T-shaped lacrimal is formed, judging by taxa with
prefrontals and T-shaped lacrimals (Gorgosaurus, Sinosauropteryx,
ornithomimosaurs, Sinornithosaurus).

> The two sides of the skull on the AMNH site
> are not consistent in their preservation, and while the projecting bone
> can be part of the prefrontal, as in *Shuvuuia,* it is likely this is a
> neomorph, and hardly consitent with either hypothesis; the left side of
> the skull shows a deeper, perhaps dissarticulated, element that
> corresponds in shape to the left side, but could also be a scleral plate,
> which even the _right_ side element could pertain to. Unlikely, but
> possible.

I highly doubt they are scleral plates.

>  The skull should be considered apart from the skeleton, in any extent,
> for its combination of troodontid-like and alvarezsaur-like features,
> which seem at odds with the skeleton's clear troodontid or
> deinonychosaur-like affinities. This does not mean then that the skull's
> alvarezsaur features can be dismissed, because the association of the
> skull and skeleton in a display (especially when the website refers to the
> skull as *Shuvuuia*) cannot be considered consistent of a phylogenetic
> inferrence or that the skull belongs to the skeleton.

Well, from what I've heard, the AMNH display indicates the skull belongs
with the skeleton.  I suppose we could ask Hwang or Norell to be sure.

Mickey Mortimer