Re: Tanystropheus & archosaur evolution

["M.Alan Kazlev" <akazlev@kheper.auz.com>]

Larry Febo wrote:

> >Date: Fri, 20 Nov 1998 08:27:58 -0500
> >From: Robert Margulski <RMarguls@cybercomm.net>
> >To: dinosaur@usc.edu
> >Subject: Re: Tanystropheus?
> >Message-ID: <3.0.3.32.19981120082758.007252c8@raven.cybercomm.net>
>
> >Please pardon my ignorance. Are you guys talking about
>
> >1) Tanystrosuchus: Kuhn, 1963 (with the long neck)
>
> >or
>
> >2) Tanystropheus: von Meyer, 1855 * (which is not presently
> >thought to be dinosaur)
>
> >or
>
> >3) I should go back and check my references and shut up.
>
> >At 07:08 11/19/1998 -0800, Larry Dunn wrote:
> >>
> >>---"Stewart, Dwight" <Dwight.Stewart@VLSI.com> wrote:
> >>>
> >>> > From: Larry Febo [SMTP:larryf@capital.net]
> >>> >
> >>> > Tanystropheus,....(got me wondering about this thing again). I
> don`t
> >>> > suppose
> >>> > anyone considers it as a possible precursor to prosauropods?
> >>>
> >>> Looking at the skeleton, I was wondering that too.  The teeth look
>
> >>> odd, though.
> >>
> >>T. isn't a dinosaur though, is it?
>
> If you haven`t deciphered from the above statements, I`m the one who`s
>
> questioning the early ancestry of  the sauropod line. Out of the
> various
> archosauromorphs , I was wondering if anyone considered the
> prolacertiform
> Tanystropheus (as in Van Meyer 1855), or the prolacertiform group in
> general
> to be the precursors to the true archosaurs. (Tantstropheus itself, I
> know,
> dosen`t have the prerequisite antorbital fenestra). They are , after
> all,
> considered as ancestral (by some) to the Pterosaurs, which are
> themselves
> archosaurs.

 well, I'm an evolutionary systematist from way back - i grew up reading
paleontology books in the pre-cladistic era & much prefer thinking in
terms of ancestor-descendent relationships rather than sister groups.  I
would thereforey envisage the following sequence as *approximating* the
evolutionary line to archosaurs & dinosaurs (reading from top to
bottom...)
------------------------------
Petrolacosaurus & Aeroscelis (Permo-Carb ancestral Diaspids)
early prolacertiforms e.g. Protorosaurus (mid Permian - ancestral
archosauromorphs)
Archosaurus & Proterosuchus (latest Permian-earliest Trias - ancestral
archosauria)
Erythosuchids & Euparkeria
undiscovered mid Trias predecessor to Ornithosuchus
Lagosuchus & co. (late mid Trias)
undiscovered early Carnian Eoraptor-like dinosaur ancestor
Staurikosaurus & Herrerasurus (proto-theropoda)
Theropoda-proper, Sauropodamorpha, & Predentata (=Ornithoischia)
-----------------------

Tanystropheus, as you point out, is not a direct anscestor.  It
represents a continuing line of prolacertiforms living alongside more
"advanced" Archosaurs.  It is NOT the ancestor to the prosauropods,
which would've evolved from a Eoraptor/Staurikosaur/Herrerasaur type
proto-dinosaur.

David Peters suggests (on his Pterosaur Home Page site) that Pterosaurs
evolved from prolacertiforms rather than lagosuchids.  As a
lay-paleo-enthusiast I myself am utterly  ignorant regarding comparative
osteology & hence unable to make any comments pro or con on that matter
however.



--
Kewl!   :-)

M.Alan

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