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Re: questions about the Odontochelys study
Mike Keesey wrote:
> What if the ventral armor was not for protection against
> but against the environment (vegetation, rocks, etc.)?
> 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
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.