Re: questions about the Odontochelys study

[Tim Williams <tijawi@yahoo.com>]

Mike Keesey wrote:

> 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.)

The ventral shield of the juvenile _Liaoningosaurus_ specimen seems to have 
been quite extensive: although only a single (left) ventral plate is preserved, 
more ventral armor is evidenced by impressions.  The belly armor of 
_Liaoningosaurus_ may have served the same purpose as that of aetosaurs - 
whatever that might be.  It may have something to do with the ability to resist 
being flipped over, and/or (as you suggest) what kind of substrata the belly 
gets exposed to during locomotion.

If _Liaoningosaurus_ is a basal ankylosaur, its body armor may not have been as 
'heavy-duty' as more derived forms.  So, _Liaoningosaurus_ may have had to rely 
more on its belly armor.

Michael Habib wrote:

> > 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?
> 
> There is also plastron reduction in Chelus fimbriatus
> (mata-mata), but they're even more aquatic than most
> chelydrids.

With the disclaimer that I don't know all that much about turtles... I do know 
that the snapping turtle and mata mata are ambush predators, so protecting the 
underside may not be so important.  Or at least, belly armor (plastron) is not 
as important as it is to aquatic turtles that spend more of their time swimming 
in the water column.  In other words, if such aquatic ambush predators spend 
much of their time motionless, with their bellies close to the sediments 
underneath, then their bellies are not as vulnerable to attacks from below - 
hence the secondarily reduced plastron.




Cheers

Tim