Re: questions about the Odontochelys study

["Jaime A. Headden" <qilongia@yahoo.com>]

Mike Keesey wrote:

<Why have no terrestrial testudines lost the plastron? Or even just reduced it? 
The only testudines with reduced plastra that I can think of are chelydrids 
(snapping turtles), and those are aquatic. Am I missing any other examples?> 

  Sea turtles, which reduce the expansion of both dorsal and ventral plates to 
finger-like strips. See also *Archelon* and kin.

  I actually find the bizarre preservation curious, the presence of a nearly 
fully formed plastron and unique ribs. All this tell me that dorsal osteoderms 
would have been present but were lost. They might simply not fuse to the ribs 
in this taxon, especially since neurals are apparently present. This seems if 
anything counter to the original presentation of dorsally bare but ventrally 
intact armor.

  The thesis that ventra armor is good for aquatic armored animals does not 
tell us why the dorsal armor of crocodilians are more dorsally than ventrally 
evident, why the aetosaurs are terrestrial but have ventral armor, etc.

  Cheers,

Jaime A. Headden

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)