Re: "real" opisthopuby (very speculative)

["Rob Schenck" <rs7286@albany.edu>]

this is interesting because just the other day I was reading a paper by
Thulborne titled  Origins of Ornithischians.  In this paper however
_euparkeria_ is considered a pseudosuchian, and the ornithischians are
thought to have resulted from the pseudosuchians, the implication being with
_euparkeria_ being on the line.  It appears that the main reasoning for this
is that the pubis of _euparkeria_ seems to be "bent" at the anterior end,
bending torwards the posterior.  This is iI guess the start of the rotation.
The next taxa presented in this phylogentic line has a well developed and
fully rotated postpubic process, with a very underdevelped prepubis, and the
postpubis is taken to be the homologue of the saurishcian pubis.  However,
_euparkeria_ is not considered a pseduosuchian anymore, and i don't think
that anyone thinks the ornithischians are derived from a pseudosuchian stock
either.  _euparkeria_ seems to have moved along with the ornithosuchians,
however,  it is not a basal dinosaur if my understanding  is correct.  So
the apparent bending or rotation of the pubis may not infact be the
ornithiscian rotation, and if anyting it would mean that all dinosaurs with
have a rotated pubis primitively ( if _euparkeria_  and is representative of
something on the line leading to dinosaurs).

what was even more interesting was that in this paper the main lines of the
ornithischians are thought ot come from a hypsilophodontian "plexus" instead
of a simple line, with things like iguanodonts beig a grade.  further more,
he lists stegosaurs as being completly unrelated to ankylosaurs, and
actually has stegosaurs, ankylosaurs and the hypsolophidont plexus all
originating near simulatneously from the pseudosuchian stock.  Of course,
this is back in 1971, and i just note it as its interesting to see how much
has drastically changed since then, while, say, Ostrom's dromaeosaur idea
has survived (for nearly as long i think right?).

the article is
Thulborn, R.A. 1971 Origins of Ornithiscians Nature 234:75-78
and there was also
1971 Zoolgical Journal of the Linnean Soceity 49(3) 235-245

as a side note, he also seems to have written an article in Paleontology in
1972 on Triassic Ornithischians, but unfortunatelty my library doesn't carry
this journal,  it has the journal of paleontology, but no "paleontology",
not the Journal of Vertebrate Paleontology either, and that REAL
frustrating.  Is there some way to get these items on line?  Or are only
synposes availible, like on Dinodata and such?

~R.

----- Original Message -----
From: "Ken Kinman" <kinman@hotmail.com>
To: <dinosaur@usc.edu>
Sent: Friday, December 07, 2001 4:14 PM
Subject: Re: "real" opisthopuby (very speculative)


> Dear All,
>      Is it possible that the prepubic process is a primitive character in
> Ornithischia, and that its gradual loss is derived.
>      And here's some wild speculation to chew on (spit it out if you don't
> like the taste)----- what if the prepubic process IS homologous to the
pubes
> in other dinosaurs, and that the postpubic process is the real neomorph?
> The postpubic process could have gradually lengthened in parallel to the
> ischium.
>      If so, ornithischians would be very propubic, and they would have
never
> exhibited either mesopuby or opisthopuby (in the sense of the pube
rotating
> backwards).  That way the pubes would have never been sticking into their
> big herbivorous guts.  And those ornithischians with extremely reduced
pubes
> may have just gradually lost the original (prepubic) process and never
have
> developed the postpubic process at all.
>          --- Just an idea,
>                     Ken Kinman
>
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