Re: Basal Ornithischia and Stegosauria

[Nick <nick.gardner@gmail.com>]

On 8/12/06, Jamie Stearns <stearns5@cox.net> wrote:
> Given that I've got a request for something on Ornithischia, I'm putting
> some of it up now.
>
> `---Saurischia
> ..`--+---Pisanosaurus
> ....|...`---Lesothosaurus
> ....|.....`--Stormbergia
> ....|.......`--Agilisaurus
> ....|.........`---Ornithopoda
> ....|...........`---Abrictosaurus
> ....|.............`--+--Heterodontosaurus
> ....|...............|...`---Lycorhinus
> ....|...............`---Pachycephalosauria
> ....|.................`---Ceratopia

Ceratopsia would be correct here, I believe. I can't comment much on
your tree, except it's not too different from what's been considered
on-list, or what has been published in Butler's 2005 paper on
Stormbergia, except he found Abrictosaurus as a heterodontosaurid, and
heterodontosaurids as a whole outside of the
Ornithopoda+Marginocephalia clade (Cerapoda?).

> ....`---Scutellosaurus
> ......`--+---Tatisaurus
> ........|...`---Emausaurus

I know Dong (1990) put Tatisaurus in the Stegosauria, I wasn't aware
this has been tested. What was your rationale in including Emausaurus
as well? I know Tracy Ford considers this apparently, but I was
curious...

> ........|.....`--+---Huayangosaurus
> ........|.........|...`---Regnosaurus
> ........|.........`---Dacentrurus
> ........|...........`---Chungkingosaurus
> ........|.............`---Chialingosaurus
> ........|...............`---Kentrosaurus
> ........|.................`---Lexovisaurus
> ........|...................`---Tuojiangosaurus
> ........|.....................`---Hesperosaurus
> ........|.......................`---Stegosaurus
> ........|.........................`---Wuerhosaurus
> ........`---Scelidosaurus
> ..........`---Ankylosauria

Ankylosauria is a stem-based clade, IIRC, so Scelidosaurus would be
included in it, not outside of it.

I can't say very much on your tree itself, except that it seems
different from the results of running Galton and Upchurch (2004). I've
not had a chance to really look at their matrix, but it seems to be
the best published thus far on stegosaurs.

> I've probably made my share of mistakes here, especially given the recent
> idea that Chialingosaurus may be invalid due the holotype material being
> missing or something. And I've recently heard that Stegosaurus was the only
> stegosaur to lack shoulder spines, not sure if this is true. If it is, it
> would be the most derived of them all.

> Do Wuerhosaurus or Hesperosaurus have
> shoulder spines?

Both are scored as unknown for parascapular spines in Galton and
Upchurch's data matrix. And Carpenter et al. didn't take note of the
absence of parascapular spines IIRC. I don't have the original
description of Wuerhosaurus, but Dong didn't comment in his chapter on
stegosaurs in Dinosaur Systematics.
>