Re: *Silesaurus*: the basalmost ornithischian after all?

["Mickey Mortimer" <Mickey_Mortimer111@msn.com>]

David Marjanovic wrote-

> - and its lack of epapophyses (which according to Fraser et al. [2002,
> description of *Agnosphitys*] are only known in "herrerasaurs and
> theropods" -- did they overlook...?).

No, I believe Fraser et al. are correct, at least in regards to axial
epipophyses.

> - herbivory, with assorted dental characters:
>     - "cheek teeth with low triangular crowns with well-developed cingulum
> beneath"
>     - "cheek teeth with crowns having low and bulbous base"
>     - "maxillary and dentary teeth with overlapping adjacent crowns" -- to
a
> very small extent in the mx, somewhat more in the d
>     - "maxillary and dentary teeth not recurved" -- well, they are, but
very
> little
>     - "maximum tooth size near middle of maxillary and dentary tooth rows"

Are any of these present in Eoraptor, with its semi-herbivorous teeth?

> - reduced postcranial pneumaticity -- at least that's how the "chonoi" of
> *Silesaurus*, which fail to enter the vertebrae, and the absence of
> pneumatic features in undoubted ornithischians can be interpreted

But is this a plesiomorphy instead?  Haven't there been studies suggesting
the supposedly pneumatic structures of erythrosuchids, crurotarsans and such
are actually vascular in nature?  While only pterosaurs, sauropods and
theropods have true pneumatic axial skeletons?

> - "large lateral process of premaxilla excluding maxilla from margin of
> external naris". I don't know how large large is, but, judging from the
> excavations on the nasal and mx, there was such an unpreserved process.
Even
> though ns and mx still met underneath it.

Eoraptor has a long process too, while Herrerasaurus' is very similar to
ornithischians' (long and broad).  Could be a dinosaurian plesiomorphy.

> - "lateral swelling of ischial tuberosity of ilium"; is this the
> antitrochanter, which according to Fraser et al. is a much more widespread
> feature?

Yup, that's an antitrochanter.

> Makes at least 6 and at most 16 characters, versus 0 to 2 that argue
> otherwise. I need not invite comments :-)

Very interesting.

> Do *Guaibasaurus* and *Saturnalia* really have completely closed acetabula
> like *Silesaurus*? :-o

Guaibasaurus has a slightly open acetabulum, as the ilial portion is
slightly concave ventrally.  Saturnalia's is "not fully open".

Mickey Mortimer