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Re: Egg sizes
Matt Fraser wrote:
> >On Wed, 5 Nov 1997, Dann Pigdon wrote:
> > Since all eggs need oxygen to survive, I would suspect that the
> > diffusive efficiency of any type of egg shell could only be stretched
> > to a certain limit, beyond which the surface area:volume ratio would be
> > insufficient.
> Right, but couldn't elongation of the egg increase the surface to volume
> ratio? Perhaps this design was used to allowable extremes.
Most of the largest dino eggs seem to be spherical, probably
to improve their structural strength. The elongated shape of many
smaller eggs may also have to do with the narrow pubic opening of
the species that layed them.
> > Could this be why most dinosaur pubic openings were suspiciously small,
> > relative to body size that is?
> Could be - good point. Clutches may have been the rule. It would seem to
> me to make more sense if the hatchling's sizes were somehow proportionate
> to those of the parent, if parental care was involved. Generally
> speaking, the larger the critter that exhibits parental care, the fewer
> and large the expected live offspring (I think that this is true).
It seems to be true of mammals, but probably not in dinosaurs.
If they were restricted by their pubic openings to laying small
eggs then even the largest of dinos probably layed a decent clutch.
Eggs may also be infertile and never hatch, so laying several is a way
of accounting for this. There is also predation to think about.
Many mammals can either run soon after birth, or can be carried by
the parents, or are hidden away in hard to get places (tree top nests,
burrows). I can't see a sauropod nesting in trees or down burrows,
or carrying small fragile eggs, and eggs are notoriously bad runners :)
> > The largest modern (well, almost) bird egg I can think of
> > would be the Madagascan elephant bird. Although it is extinct the eggs
> > are occationally found buried in sand dunes, which was apparently
> > how they were incubated. It would be interesting to know whether any
> > dinosaur eggs are known to excede this egg size.
> Yep, and if there were none that did, what does that say about parental
> care, etc.
Most modern flightless birds also lay large clutches, in
fact an emu or ostrich clutch is often much larger than those of
smaller flying birds. I think it would take just as much parental
care to look after a large clutch of eggs as it would for a single
egg, especially so once they hatched.