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Re: Tanystropheus ?



Nov. 21, 1998, M.Alan Kazlev wrote:

>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.


Thanks for that rundown. I thought it went something like that, except I`ve
read somewhere that Pseudosuchians were stressed as the starting point of
the dinosaur line. I know the interrelationship of these early groups are
somewhat complex, and to an extent still not entirely determined. I`m
getting a hold of Sereno`s dissertation on early archosaurs which should
shed more light on the subject (for me anyway).

I wasn`t sure they could determine sauropod type features in Eoraptor and
Herrerosaurus  I thought they were strictly pre-theropod forms, hence
sauropod splitting off at an earlier time. I admit not knowing much about
the detailed skeletal structures and how to interpret it yet (which I hope
to remedy soon).

Of course, I`m also predjudiced by my "theory" of a common pterosaur-bird
ancestor  of which Cosesaurus suggests itself...which in turn would suggest
a branching off of the sauropod-ornithischian line before this
Prolacertilian lost digits and became airborne. ..and (don`t you know),
there`s Tanystropheus sitting there with its long neck. (an early expression
of that particular gene pool?). This (of course) may all prove wrong, but
I`m determined to investigate it anyway. Can`t hurt in taking a look.

Lagosuchus I would think was a secondarily flightless form, descended from
Pterosaurs. (here again, I think a ground up model of flight development
unlikely).