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Re: questions about the Odontochelys study



No, I do not have reasons, but neither do I have for the other way.
The pleurodire strucked me as too fast. Of course, velocities should
be measured to give a more serious statement. I did not know of
something similar of a "high march" for the matamata, but in any case,
an upright stance does not necessarily have to do with velocity.

With respect to permitting a greater amount of limb movility, it is
right when shell coverage is reduced around the limbs, but I think it
has nothing to do when related to the space between costal
plates/ribs, as for example in Archelon. In any case, there are also
pelagic sea turtles, which also performs subaqueous flight, with a
complete shell coverage without fenestras.

In addition, it was mentioned above a terrestrial turtle with reduced
carapace, so the loss of shell coverage may relate to something
different to specific adaptation to aquatic movements, at least for
those parts different from around the legs. Granted, I'm somewhat
Gouldian. Too many Natural History columns to pass unaffected.

2008/12/3 Mike Habib <habib@jhmi.edu>:
>
> Augusto Haro wrote:
>
>>>>
>> All right, but it was just an example that turtles with a heavy
>> cuirass are relatively fast, and that I doubt that turtles with less
>> completely covering shells, as the snapping, can really be faster.
>> Just to say I do not know exactly to what is decreased coverage of the
>> bony shell in turtles related.
>
>
> Is there a particular reason that you doubt a chelydrid could be faster?  In
> any case, the shell reduction, especially in the plastron, might have more
> impact on aquatic locomotion than terrestrial walking.  For mata-matas, as
> least, the plastron reduction allows the animals to take a somewhat more
> erect stance when punting along the bottom, and appears to greatly increase
> effective stride and speed (they're actually quite rapid movers when need
> be).  This is all unpublished, personal observation, however (albeit many
> years of personal observ. for that particular taxon).
>
> For pelagic aquaflyers, specifics of shell reduction or expansion might be
> related to required forelimb excursions, as well as the specific bracing
> important for mirrored stroke utilization (I recommend taking a look at
> Stephen Godfrey's 1984 manuscript on plesiosaur locomotion and aquaflying).
>
> Cheers,
>
> --Mike
>
>
> Michael Habib, M.S.
> PhD. Candidate
> Center for Functional Anatomy and Evolution
> Johns Hopkins School of Medicine
> 1830 E. Monument Street
> Baltimore, MD 21205
> (443) 280-0181
> habib@jhmi.edu
>
>
>