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Re: Obligatory parental nest attendance.



John Bois wrote:
> 
> I was wondering if anyone would care to comment on this idea?
> Oxygen is limiting for underground nests.  Many dinosaurs oviposited in
> sand.  Dinosaur eggs were bigger (in general) than turtle and crocodile
> eggs.  They therefore required more oxygen.  They also probably had a
> higher rate of embryonic growth, and so needed even more oxygen.  These
> together made it necessary to have eggs closer to thwe surface in
> order to access that oxygen.  If this were all true, their eggs would not
> have the moderating  effect that a thick layer of sand would provide.  The
> only way to provide this would be for a parent to modulate the various
> optima, by warming, shading, ventilating, etc.
> I seem to remember that most late-cretaceous nests are fairly shallow.
> Comments on or offline appreciated.

This is precisely what megapodes (like the Australian brush turkey)
do. The male of most species tend the nest mound carefully, and a
temperature receptor in their beak helps them to decide whether the
eggs need to be covered more or uncovered. However this seems to have
more to do with temperature control than it does oxygen supply.

Apparently the Madagascan elephant birds incubated their eggs by
burying them in sand, and those eggs were huge. Remember that plant
roots need oxygen too, so I suspect that in all but the most hard
packed soils that there is plenty of oxygen to go around. Turtle
eggs are usually buried quite deep - I've seen people excavating them
have to plunge their entire arm up to the shoulder down into
the hole.
-- 
____________________________________________________
        Dann Pigdon
        Melbourne, Australia

        Dinosaur Reconstructions:
        http://www.geocities.com/capecanaveral/4459/
        Australian Dinosaurs:
        http://www.alphalink.com.au/~dannj
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