Question on turtle shells

[Martin Baeker <martin.baeker@tu-bs.de>]

Al long time ago I read in a book on extinct marine reptiles (I think
it was by Augusta) that there are marine turtles that have a
complicated evolutionary history where they lost the shell ,
re-evolved it (with a different bauplan), and lost it again.

However, I have completely forgotten all details. Is there any truth to
this? Does anyone have a reference?

Thanks a lot,

Martin.

                   Priv.-Doz. Dr. Martin Bäker
                   Institut für Werkstoffe
                   Technische Universität Braunschweig
                   Langer Kamp 8
                   38106 Braunschweig
                   Germany
                   Tel.: 00-49-531-391-3073
                   Fax   00-49-531-391-3058
                   e-mail <martin.baeker@tu-bs.de>