Egg questions (was: Re: Allosaur baby faces)

[Jura <pristichampsus@yahoo.com>]

--- Christopher Taylor <ck.taylor@auckland.ac.nz>
wrote:

>     Which reminds me of another question I was
> thinking of asking - does
> anyone know if coelurosaurs laid hard-shelled eggs
> like modern birds, or
> leathery-shelled eggs like other reptiles? What is
> the earliest branch on
> the avian stem that we can be sure laid a hard egg?
> I ask because I was
> wondering if well-known stem birds such as
> Hesperornithiformes and
> _Ichthyornis_, which are commonly (albeit perhaps
> mistakenly) assumed to be
> biologically much the same as modern birds, can be
> assumed to lay a hard
> egg. Considering how difficult it is to imagine
> _Hesperornis_ moving at all
> on land, could it have even produced live young?
> (That last is rampant
> speculation, which I don't support in any way)
 
++++++++++++++++++++++++++++++++++++

I'll leave the answer to this question to more
qualified individuals. Offhand, though, I think
coelurosaurs are believed to have had hard shelled
eggs. Incidentally, not all reptiles lay leathery
eggs. Most tortoises are hard shelled egg layers,
along with most geckos. Hard shells seem to be useful
in areas low in humidity (leathery eggs are better at
gaining water and are often associated with areas of
high humidity).

Anyway, I have a follow up question to Chris's. How do
we tell the differences between leathery and hard, in
a fossilized egg? Furthermore, have there been any
fossil eggs of crocodilians, or squamates, or anything
that isn't a dinosaur; which might be used for
comparison. 

For instance, can we tell if the recently described
pterosaur eggs were leathery, or hard shelled?

Jason

"I am impressed by the fact that we know less about many modern [reptile] types 
than we do of many fossil groups." - Alfred S. Romer

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