Re: THE TURTLE PROBLEM

[Pieter.Depuydt@rug.ac.be]

> > Rieppel also considers turtles and placodonts as sister groups if 
> > memory serves, so in his view, turtles are extant Sauropterygia...
> > Right?

> It would seem so - but you think I believe *this*? I like my turtles as good
> little parareptiles.

I am not particular fond of Rieppel's turtle idea either, I was just 
extending the line of his reasoning. (I think the Henodus/Placochelys 
turtle like body is a nice example of convergence).
By the way, in one of the last Science issues (I don't have the 
reference at hand) Benton recapitulates the cladistic analysis of 
turtle relationships; his conclusion is (if I remember correctly) it 
takes only three or something additional steps to move turtles from 
Sauropterygia to Parareptilia, without affecting the relationships of 
the other groups. Conclusion: we cannot know and turtles remain a 
beautiful mystery.
However again molecular data could help. In the parareptile turtle 
hypothesis, crocodiles are more related to lizards than each is to 
turtles, in the sauropterygian turtle hypothesis, lizards are more 
related to turtles than each is to crocodiles.
(If it is of course accepted that Sauropterygia is closer to the 
lepidosaur clade than to the archosaur clade). 

Pieter Depuydt