Re: turtles, mammals and rattlesnakes...

[Thomas_R_HOLTZ@umail.umd.edu (th81)]

>> 
>> According to the NH article, turtles evolved during the Permian period
>> from a group of animals known as pareiasaurs.  What I'm wondering is
>> a) how secure is the conclusion that turtles arose via that lineage,
>> and b) given that we accept it, how much help does that give us in
>> determining where the turtle/snake/mammal splits occurred?  
>
>This probably refers to the work by Michael Lee, who has described several
>shared derived characteristics linking turtles to pareiasaurs.  I believe it
>has been published in Science.  I have seen him present this work, and 
>discussed it with him, and it seems very convincing.  As pareiasaurs were 
>previously thought to be a sister group to Chelonia, I don't see how this
>adds to the mammal/reptile relationship debate..

At present, I believe that there are two main camps concerning turtle
origins.  Both agree that turtles are within a group (Parareptilia) which
contains several extinct forms.  Lee favors a relationship with
Pareiasauria.  Reisz and others think that pareiasaurs are the sister group
to the Chelonia-Procolophonida clade (procolophonids are small forms which
looked like fat spiky lizards).  Personally, I'm a little far removed from
this debate.  Either idea seems reasonable to me.

>
>Tony Canning
>tonyc@foe.co.uk
>
>

Thomas R. HOLTZ
Vertebrate Paleontologist, Dept. of Geology
Email:Thomas_R_HOLTZ@umail.umd.edu (th81)
Phone:301-405-4084