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Re: ARCHOSAURIAN TURTLES?
>Date: Sat, 29 May 1999 09:28:37 PDT
>From: "Matthew Troutman" <firstname.lastname@example.org>
>Subject: ARCHOSAURIAN TURTLES?
><<The theory of relativity does predict events not available for study,
>but so does cladistics. You said yourself we don't have all the
>fossils, and one doesn't always get an "answer" they were looking for.
> Take Olivier Rieppel at the Field Museum whose recent cladistical
>analysis suggests turtles may be archosaurs! Since the common
>"accepted" hypothesis was that turtles represented anapsids, the most
>ancient and "primitive" reptiles, Rieppel should have gotten what everyone
>else did if there was no real predictive power or everything was
>in cladistic methodology. Instead, many researchers have good reason to go
>back and look at turtles more seriously. Are they archosaurs? That's the
>risky prediction, without lots of fossils pointing the way.>>
>Rieppel didn't suggest that turtles were archosaurs, that was Hedges and
>Poling (1999). Rieppel found out in his 1993 analysis trying to determine
>sauropterygian ("euryapsid" in the paper) relations, that turtles fall
>to diapsids (above captorhinids) as a whole with the particular data set he
>was using. Most prominently with Michael DeBraga (1997), Rieppel found
>turtles are probably lepidosauromorphs, based on several features but most
>prominently the advanced mesotarsal ankle joint (note that Hedges and
>have turtles as closer to crocodilians than birds, but it is the bird group
>that has the AM ankle). Rieppel (1999) summarized his findings quite
>eloquently in his commentary on Hedges and Poling's molecular analysis.
>Also of interest is that he cites a paper in prep with Riesz that shows (as
>his many earlier analyses did) that sauropterygians are probably the
>relatives to turtles. Rieppel (1998) shows Testudines as a sister-group to
>thallatosaurians+sauropterygians (another new arrangement).
Hmmm....I remember backing down from my theory that diapsids may have
developed from the synapsid condition (somewhat embarrassingly I might add)
when I realized that what I was saying implied that turtles (as anapsid
representatives) should therefore be more closely related to humans than
birds! Now,...if turtles are actually lepidosaurian.........I may still be
on the right track about a one time only development of the "warm-blooded"
condition in terrestrial vertebrates.