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

["David Marjanovic" <david.marjanovic@gmx.at>]

>   The actual spelling of the name is *Agnostiphys,* not *Agnosphitys;*
check comments online, from Darren Naish and others.

That's what I did. And it's Darren's comment which, for reasons that are
unknown to me, states that *Agnosphitys* is the intended spelling.

> <But it shares with ornithischians, to the exclusion of (basal)
saurischians, the following features (quotes from Glut's
> encyclopedia, p. 62):
>
>   - herbivory, with assorted dental characters:
>     - [...]>
>
>   "Herbivory" should, expectantly, form the same or similar complex of
anatomical features in a jaw among dissimilar animals.

That's why I listed it as one character with several details, and counted it
as one in the minimal list (of 6).

> virtually identical to traversodont cynodontian and multituberculate
molars.

Don't know what you mean, because those 2 look very different from each
other.

> so that Glut's quote, presumably from the 3rd supplement,

No, from the original. The 3rd isn't published yet!

> <  - a beak on the tip of the lower jaw. There is no predentary, but
because the beak must have come before the predentary (assuming
> that the predentary, like the rostral, evolved to give additional support
to the beak), this should not exclude *Silesaurus* from
> being the basalmost ornithischian.>
>
>   This doesn't really work as most work appears to support that a
keratinous beak it not neccessary for either herbivory,

I agree, considering the sheer number of beakless herbivores! Note it's the
next character in my list, not included in the herbivory complex.

> or formed prior to a toothless jaw.

More or less at the same time, I assume.

> It seems likely, but there has yet to be any proof for this. The lower
jaw's "hook" apparently interacted
> only with teeth, as it is narrower than the paired premaxillary dentition,
so the possibility of a lower "beak" to propose the
> presence of an upper beak, as in ornithischians, co-existent with a
reduction in dentition relative to premaxillary length, is not
> viable.

I don't! I propose the presence of a lower beak but not of an upper beak in
*Silesaurus*! As I wrote: "a beak on the tip of the lower jaw" and nowhere
else. Half a beak, if you like.

> The "hook" therefore may have served a separate function than cropping
vegetation; the paired dentaries would form a apex in
> cross-section higher medially than laterally, and is remarkably unlike
that of the predentary morphology of basal ornithischians,
> and I would suggest that it not be considered homologous to the predentary
of ornithischians.

I don't consider the tips of the dentary homologous to the predentary! :-)
How could I?!? I just entertain the possibility that the rhamphotheca which
covered them could be homologous. And this I base on another possibility,
namely that the predentary could be an "ossification of the beak", like the
rostral.

> < - 4 sacrals (respectively 4 fused vertebrae, 2 of which contact the
ilia). Ornithischians start at 5 (all of which contact the
> ilia), basal saurischians retain 2.>
>
>   This doesn't really support anything. *Eoraptor,* as stated elsewhere,
has _three_ not _two_ sacrals.

Could be convergence in both cases. I just say it is one character, not
less, not more.

> The condition in *Silesaurus* appears to be unique,

Of course. But because it is not impossible that the 5 sacrals of
ornithischians evolved via such a condition (note my cautious wording), I
added it to the list.

> < - the lack of the 5th toe.>
>
>   Pardon? The fifth metatarsal in some saurischians has a phalanx on it,
but this is hardly a toe.

Sure it is. :-) OK: "the lack of phalanges on the 5th pedal digit". Better
that way?

> However, because the foot of
> *Silesaurus* is so derived, with a fifth metatarsal that is shortened and
semilunate as in tetanuran theropods only,

It's commonly absent in ornithischians.

> this is unlikely to be a condition relating to ornithischians, especially
as the foot has other advanced, cursorial adaptation (short toes,
> shortened second and fourth metatarsals relative to the third) that is
unlike anything but a theropod.

Perhaps the loss of the 5th toe is a cursorial adaptation of Ornithischia
including *Silesaurus*, and then *Silesaurus* added more cursorial
adaptations that the undoubted ornithischians didn't add.

> < - a (slight) crossing of radius and ulna>
>
>   Highly plesiomorphic, as both ornithischians and saurischians have
crossed ulnae.

Theropods don't, sauropods don't, crocodiles don't. Herrerasaurids don't
either, AFAIK. Do basal sauropodomorphs? Has there been enough research to
tell?
        I agree it's likely an adaptation to quadrupedality.

> the long forelimbs thus argue for quadrupedal adaptations and, like the
> (obviously non-ornithischian *Marasuchus* which has similar limbs, or
*Lewisuchus* with similar
> humerus, or *Scleromochlus* with similar limb structures as well).

Yes?

> < - 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.>
>
>   "Reduced" argues there was some to begin with, and the condition was
reversed.

Yes. That's an interpretation of mine -- as I wrote.

> However, if the argument is due to vertebral "chonoi" or the "chonoses"
between successive
> vertebrae, or the fossae between the centrodiapophyseal laminae of the the
vertebrae themselves, these are also present in
> non-dinosaurs like *Marasuchus* and *Lewisuchus* and are limited in
*Herrerasaurus* and other basal dinosaurs, implying this is a
> plesiomorphy, and is "incipient," rather than "reduced." Neurocentral or
central fossae do not occur in basal theropods, and are
> unexpected to occur.

OK.

> The conclusion should favor that this form is not a dinosaur based on the
use of Ornithischia +
> Saurischia.

What are, now, the synapomorphies of Dinosauria?

> Dzik's usage of herbivorous adaptations to propose an ornithischian
identity as being possible

He doesn't do that. He uses e. g. the beak.

> If there is anyone with cited research on *Chindesaurus*
> as a poposaurid or other rauisuchian/basal crocodylomorphan, I (and David,
I am sure)would love to see it.

Of course. :-)