Re: questions about the Odontochelys study

["T. Michael Keesey" <keesey@gmail.com>]

On Sun, Nov 30, 2008 at 5:35 PM, Tim Williams <tijawi@yahoo.com> wrote:
>
> On a separate issue, the presence of a plastron is said to be an indication 
> of an aquatic origin of turtles, because it provides protection for the 
> ventral body surface.  In terrestrial tetrapods, by contrast, the belly is 
> not exposed to predators unless the animal is rolled over.  For that reason, 
> the bellies of ankylosaurs are far less heavily armored than their backs.  
> However, one ankylosaur (_Liaoningosaurus_, based on a juvenile specimen) 
> does have quite a large "shell-like" ventral abdominal plate to protect the 
> underside close to the hips.  Rather than suggesting aquatic adaptations (!), 
> it may indicate that juveniles of this species were more prone to be rolled 
> over (such as by predators).  So would an adult _Liaoningosaurus_ be expected 
> to have such a large ventral plate as well?  If so, why?

What if the ventral armor was not for protection against predation,
but against the environment (vegetation, rocks, etc.)? (Probably
overkill, but I thought I'd toss the idea out there.)

Related question: 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?

-- 
T. Michael Keesey
Technical Consultant and Developer, Internet Technologies
Glendale, California