Re: questions about the Odontochelys study

[Graydon <oak@uniserve.com>]

On Sun, Nov 30, 2008 at 08:04:03PM -0800, Jaime A. Headden scripsit:
>   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.

Didn't someone manage to show that croc armor is more of an exoskeletal
back support than armor, as such?  Which would make the dorsal part more
important than the ventral part.

Ventral armor in aetosaurs, well, three things come to mind:
        - risk of being flipped and attacked on the ventral side by
          predators provides selection pressure for ventral armor
        - a low centre of mass helps with avoiding being flipped over in the
          first place, so belly armour is selected for as part of selection
for a low centre of mass 
        - the genetic pathways to grow dermal armour grow dermal armour,
          without being all that specific about location; especially if the
pathways are associated with ribs, and gastralia are still present,
this would tend to make armour something that developed generally,
rather than specifically.  (Don't know if gastralia are known from
aetosaurs or not.)

-- Graydon