RE: On the subject of mysterious absences...The Answer

[Tim Williams <twilliams_alpha@hotmail.com>]

Adam (adam@crowlspace.com) wrote:  

> Tim, whatever you wrote got chewed by the list-server, but Dan seems to
> have responded to it. What did the original say as he only preserves
> part in his reply?  


Yeah, sorry about that.  David's response preserves most of my original 
message.  


I'll add that the following paper offers a nice summary, despite being nearly 
10 years old.  Although the authors recover a turtle+sauropterygian clade 
(within Lepidosauromorpha), they do discuss some of the problems associated 
with pinning down turtle relationships.  


Rieppel O. & Reisz, R.R. (1999). The origin and early evolution of turtles. 
Annual Review of Ecology and Systematics 30: 1-22.   


Abstract: "A critical reexamination of turtle relationships continues to 
support asister-group relationship of turtles with a clade of marine reptiles, 
Sauropterygia, within crown-group Diapsida (Sauria).  The high Homoplasy Index 
raises concerns about the phylogenetic information content of various 
morphological characters in broad scale phylogenetic analyses.  Such analyses 
may also suffer from inadequate statements of primary homology.  Several such 
statements that have played an important role in the analysis of turtle 
relationships (dermal armor, acromion, astragalo-calcaneal complex, hooked 
fifth metatarsal) are reviewed in detail.  An evolutionary scenario for the 
origin of the turtle bauplan suggests an aquatic origin of turtles, which is 
supported not only by their sauropterygian relationships, but also by 
paleobiogeographic and stratigraphic considerations.  However, turtle 
relationships remain labile, and further investigations of their relationships 
are required,
 involving molecular and physiological data."  


Cheers 

Tim     
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