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> This could obviously be solved by evolving a soft
> shell (and then abandoning
> it altogether). The textbook explanation
> (...assuming there really is a
> textbook that mentions this question!) is that
> because archosaurs store the
> calcium the embryo needs in the shell and not in the
> yolk, the hard shell
> can't be abandoned, but I have no idea how testable
> this really is. It
> certainly sounds neat, however.
Should be testable by now by a dedicated researcher,
but to me it sounds like something not too hard to
reverse. What cods and Arctic sharks, inter alia, do
with their liver suggests that lipid storage and
calcium metabolism are natural buddies.
So reading it the other way around - no
(ovo)viviparous dinos because no marine dinos until
Neornithes - would work as well, because there was no
real advantage gained from ovovivipary.
There are ovoviviparous lizards and snakes (e.g.
Lacerta vivipara, Vipera spp.) at least some of which
are thus enabled to settle montane and subarctic
habitat. So it *can* happen, but it is certainly
adaptive and comes at some unkown cost (the cost is
there or else it woulsd be more widespread). Of
course, during the Cretaceous, there cannot have been
much of this habitat around...
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