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

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

> <I agree, considering the sheer number of beakless herbivores! Note it's
the next character in my list, not included in the
> herbivory complex.>
>
>   Note above. Perhaps it should have been included in the list.

Certainly not, given e. g. the beaklessness of sauropodomorphs.

> The argument for the presence of a beak in the upper
> jaw of basal ornithischians like *Lesothosaurus*

is irrelevant to this discussion, because (for the 3rd time) I don't argue
for the presence of a beak in the upper jaw of *Silesaurus*.

>   If taken as a series of acquisitions, I would say it has a _major_
impact on the issue. "Four" vertebrae incorporated into the
> sacrum, versus just "sacrals" touching the ilia, would be treated as a
state of a separate character that has to be considered in
> light of other taxa.

Yeah, sure. My point is that 2 "true" sacrals + 2 "sacrodorsals" may be an
intermediate between 2 sacrals + 2 dorsals (plesiomorphy) and 4 "true"
sacrals (derived ornithischians).

> In *Lesothosaurus,* only three scrals contact the ilia,

Good to know.

> <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.>
>
>   Yet the conditions as they are are not the same, and such a hypothetical
scenario shouldn't be used as an apomorphies,

As a possible apomorphy. :-)

> especially since the orinithischian and *Silesaurus* sacra
> are distinct fomr one another under the listed condition.

Perhaps this doesn't stop *S.* from being the _basalmost_ ornithischian.

> <Sure it is. :-) OK: "the lack of phalanges on the 5th pedal digit".
Better that way?>
>
>   Yes. But then, retention of the tow could be a saurischian apomorphy, as
well.

Retention is by definition a plesiomorphy.

>   While basal ornithischians reversed the other features, including
convergent femoral anatomy with saurischians, the ascending
> process shifted laterally ... again ... the calcaneum shrunk (being
primitively large in basal ornithischians and saurischians but
> tiny in *Silesaurus* as in tetanuran theropods with a semilunate aspect.

You're right, I ignored the femur. Have yet to compare...

> <Theropods don't, sauropods don't, crocodiles don't. Herrerasaurids don't
either, AFAIK. Do basal sauropodomorphs? Has there been
> enough research to tell?>

In the same issue, HP Matt Bonnan argues that herrerasaurids and at least
*Plateosaurus* were incapable of pronation. Is there any quadrupedal
prosauropod trackway? Because in this case the fingers should point
laterally. Must look strange. I don't know if the wrist would allow it (mine
does).

>   Contrary in these observations, theropods do have crossed unlae, as do
"prosauropods." But perhaps I should clarify that when the
> radius progressed from the lateral humeral condyle to the medial wrist,
and the wrist is perpendicular to the distal humeral
> transverse axis, the wrist in lateral view does not look crossed; this is
still crossed when one looks in cranial view.

Yes, but very slightly. In lateral view they look parallel, and that's my
point. That's no comparison to mammals, undoubted ornithischians, and even
*Silesaurus*.

> In quadrupedal animals such as thyreophorans and articulated
*Heterodontosaurus* [...], the manus faced
> cranially without any adequate alteration of the distal humerus to permit
the radius _not_ to cross the ulna

That, too, is my point.

> and the monograph is not out yet (soon...).

:-)

>   Crocodilian distal wrists bave bones between the radius and ulna (ulnare
and intermedium) which are expanded and provide a carpal
> block that prevents the radius from crossing the ulna. This is seen in
lacertilians, amphibians, etc. As a secondary conclusion,
> pronation of the wrist does not require a radius to cross an ulna,

In crocs, the hands are not pronated, instead the forelimbs sprawl enough to
make the hands face cranially. In amphibians, the fused radioulna can rotate
about its long axis, as I learned from HP Matt Bonnan's paper.

> <<...[T]he 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?>
>
>   I was hoping it was obvious that the limb structure is similar to
non-dinosaurian archosaurs, and may allude to the plesiomorphic
> nature of the limb structure, but this does not seem to have been the
clearest case.

You apparently didn't finish the sentence. You have "and, like the", then
the parentheses, and then the full stop.

>   And writing that, I had this odd, bizarre tought that had nothing to do
with the jaws but has been regarded in the past. As the
> oldest dinosauriform with a fully tridactyl pes, footprints regarded as
Middle Triassic to early Late Triassic in age do not
> neccessarily need to be theropodan.

Indeed.

> Oh, and that Avepoda now includes ALL dinosaurs and *Silesaurus,* if it's
a non dinosaur, as it
> possesses the first occurence in common with birds of a metatarsal I [or
even, with a stretch, an mtV] that does not contact the
> tarsus and a fully tridactly pes (I mean, hell, there may not even be a
first toe anyway).

Because this condition is not homologous to that in birds, Avepoda does not
include *Silesaurus*.