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Re: questions about the Odontochelys study
Jason <firstname.lastname@example.org> wrote:
> Admittedly, the discovery of _Odontochelys_ has me leaning
> a bit more towards Sauropterygia now, but I'd still
> argue that the procolophonid hypothesis is at least as
Also, I don't know if the inclusion of _Odontochelys_ into the matrix boosted
the support for the Testudines+Sauropterygia clade above the measly 53% found
> Prior to the embryological discovery that turtles evolved
> the plastron first, a good alternative argument for plastral
> evolution was that it served as a brace for the carapace. By
> connecting both sides of the carapace together through the
> plastron, the chelonian shell was significantly
Is this why terrestrial tortoises tend to retain the plastron?
> While this no longer seems feasible for turtles, it might
> have held for ankylosaurs; at least _Liaoningosaurus_.
By comparison, other juvenile nodosaur specimens (such as the "scuteling" from
Fort Worth TX, and _Anoplosaurus_ from England) were found without any
associated dermal armor, presumably because it had not yet ossified. Or maybe
the difference was taphonomic - i.e., something about the circumstances
surrounding the preservation of _Liaoningosaurus_ allowed part of the dermal
armor to be fossilized, despite it being not fully ossified?
> Perhaps the little guy got stepped on a lot. :)
My guess is that the armor made baby _Liaoningosaurus_ just a little bit
crunchier when it was being chomped on by a predator. Those little plates
might have gotten stuck between the predator's teeth. :-)
> I don't have the _Liaoningosaurus_ paper, so I'm
> not sure if this ventral plating ever connected to the
> dorsal armour, or if it was on its own.
There doesn't seem to be any connection; the only dorsal armor preserved
appears to be a bunch of stegosaur-like plates close to the pectoral girdle.
These subtriangular plates are interpreted as being vertical in life. So
overall, based solely on the preserved armor, the belly of _Liaoningosaurus_
seems to have been much better protected than the back and sides. (Or again,
this might be taphonomic.)
(BTW, in a previous message I mentioned that the left ventral plate was
preserved. My mistake - it was the right one. The left one is only an
impression - like the anterior ventral plates.)