Re: Tanystropheus & archosaur evolution

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

Larry Dunn wrote:

> ---"M.Alan Kazlev" <akazlev@kheper.auz.com> wrote:
>
> > 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.
>
> My understanding is that Eoraptor and (even more so) Herrasaurus are
> basal Theropoda rather than basal Dinosauria (although others say that
>
> Eoraptor is not a dinosaur at all).  Haven't been looking at
> Sturikosaurus, though.

yes - there seem to be two interpretations - one has Herrerasaurus & co
as basal theropods, another as basal dinosaurs.  I prefer the 2nd
interpretation, if only because:

(a) there logically WERE basal dinos somewhere, and

(b) one would expect that at least SOME (even if fragmentary) their
remains are therefore likely to have turned up in the various rich
early-late Triassic (Carnian) tetrapod assemblages (Ischigualasta, Santa
Maria, Popo Agie, Lower Docum, Maleri, etc,) and so therefore

(c) if Herrerasaurus & co are NOT basal dinos, then where the frig ARE
those beasts?

Of course, one way around this cunundrum would be to say that the
Theropoda themselves are the basal stem from which the other lines of
dinos (sauropodamorph & ornithischia) evolved.

Taxon Herrerasauria therefore becomes a suborder of Order Theropoda,
Superorder Dinosauria (or at least that's how I'd put it in my
acladistic frame of reference)

--
Kewl!   :-)

M.Alan

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