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shell thickness - Bigelow; also pores
>Regarding the discussion on whether the thickness of the ?T. bataar
>a diagenetic feature or is original structure:
>A 1992 paper by Karl Hirsch and Rolf Kohring (Jour. Vert. Paleo.
>describes some crocodillian eggs from the Eocene of Wyoming. They note
>the fossil croc. eggs are 65-68 mm long, and 0.6 mm thick.
>From some quick math on my part:
>This thickness is _proportionally_ slightly over twice as thick as the
>_proportion_ in the ?T. bataar eggs, if that is the true T. bataar
Yes, and on average dinosaur eggshell is proportionally thinner than a
comparable sized bird egg.
> They noted no dissolution effects on the outer surface of the egg
>Prisms and plates of calcite on the inner surface of the shell does, in
>places, appear to be, in their words, "eroded".
Yes, that is due to the embryo removing calcite from the mammillae.
Eroded mammilae is typical
of hatched eggs.
> The ?T. bataar eggshell may have experienced some degree of
>to a smaller thickness; however, this doesn't seem to be universally so
>all fossil eggs. A blanket statement that dismisses egg thickness as
>unusual is probably premature.
You misunderstood me. Telescoping is common in elongated eggs standing
on end. The result is
a shortening of length, it does not affect shell thickness. I gave no
blanket statement dismissing
shell thickness. In fact, it is used in the diagnosis of egg taxa.
>It may relate to how the eggs were layed, buried,
>or even incubated.
Perhaps, but less than you might expect. Actually it is the gas
conductance values of the egg
shells that provide the most clues to the nesting environment.
>Shell thickness is not just a side-show curiosity.
I never said it was.
>From personal experience, I have seen the effects of pressure solution
>fossil mollusk shells in thin section, and the pitting, embedded quartz
>grains, and resultant neomorphism of prisms is unmistakable. It should
>be easy to resolve this discussion regarding the ?T. bataar material.
Certainly, but I was not referring to diagenesis. My understanding of
Neil was that he was
stating that compaction would thin the eggs.
>it would be interesting to compare the shell pore density on modern
>crocodylian eggs, ostrich eggs, and the ?T. bataar eggs. This may give
>some clue as to what the _relative_ embryonic metabolisms are for these
>groups of archosaurs...at least, in my opinion>. Oxygen uptake, you
Done a long time ago: Seymour, R., and Ackerman, R. 1980. Adaptations to
in birds and reptiles. American Zoologist 20:437-447.
Ackerman, R. 1980. Physiological and ecological aspects of gas
exchange by sea turtle eggs.
American Zoologist 20:575-583.
Board, R. 1980. Porosity of the avian eggshell. American Zoologist
Mou Y., 1992. Nest environments of the Late Cretaceous dinosaur eggs
from Nanxiong Basin,
Guangdong Province. PalAsiatica Vertebrata 30:120-134.
Paganelli, C. 1980. The physics of gas exchange across the avian
eggshell. American Zoologist
Sabat, K. 1991. Upper Cretaceous amniotic eggs from the Gobi Desert.
Seymour, R. 1979. Dinosaur eggs: gas conductance through the shell,
waqter loss during
incubation and clutch size. Paleobiology 5:1-11.
Seymour, R., 1980. Dinosaur eggs: the relationships between gas
conductance values through
the shell, water loss during incubation and clutch size. M moires
Societe Geologique de France