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Re: Nature's pterosaurs
Alan Brush (email@example.com) wrote:
<If it is valid to assume both specimens are pterosaurs and therefore
related, how significant does this difference become. There have been
numerous studies on the physiology of Ca and the proteins in avian
eggshells, not as much on why reptile shells are different. The assumption
has been that the leathery condition is basal and the calcified shell
derived. There reports put both systems in the same group with all the
implications of metabolism of Ca, vitamin D, and the included proteins.
There would also be mechanical and behavioral differences associated with
the hatching process. Astonishing!>
I think that the criteria listed for a "leathery" shell in the chinese
pterosaur is applied by the adherence to a rounded shape of the shell
margin, showing "no" breakage. But this is true in several fossil
hard-shelled eggs. Even in the one Liaoning bird preserved as an embryo,
the outline as an egg remains stable, showing adherence to shell margin,
wether hard or not. It may be that the "leathery" shell is not what it
seems. The other pterosaur embryo shows a rounded eggshell margin, but
only fragments of actual shell (erosion), but this may imply fracturing of
the shell during compression, as happens during more 3D shell preservation
(say, *Maiasaura* and *Hypselosaurus* eggs and those of the Gobi Desert).
Jaime A. Headden
Little steps are often the hardest to take. We are too used to making leaps
in the face of adversity, that a simple skip is so hard to do. We should all
learn to walk soft, walk small, see the world around us rather than zoom by it.
"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)
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