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Re: Meter-wide "dinosaur" eggs reportedly found in Chechnya
Kiwis are astonishing creatures - I have seen an x-ray of a kiwi with an egg in
the oviduct, and it certainly takes up a good deal of space!
Another point should be reproductive strategy. Even in a large animal egg size
relates at some level to clutch size. The kiwi, of course, has a clutch size of
one, but faces (or at least faced before we got to New Zealand with a bunch if
exotics in tow) no really serious predation risk. The larger ratites (and
presumably larger birds of other affinities, such as Dromornithids?) lay larger
clutches (often with several females depositing in a common nest) and so, of
course, did at least some non-avian dinosaurs. As I recall ostrich eggs are
actually on the small side as bird eggs go in relation to the size of the
adult. One wonders what the clutch size of Aepyornis would have been!
1825 Shady Creek Court
Canada L5L 3W2
On 2012-04-16, at 12:58 AM, Tim Williams <firstname.lastname@example.org> wrote:
> Dr Ronald Orenstein <email@example.com> wrote:
>> Would these considerations apply only to hard-shelled eggs that had to fit
>> in the oviduct and pass through the pelvic girdle? Would a flexible-
>> shelled, elongate egg (say) have been bound by different size constraints
>> (though a soft shell might tear more easily on a heavier egg)?
> Yes, at some point an egg simply becomes too big to be held inside the
> body, and laid. The largest egg relative to the mother's body size is
> not found in the largest flightless birds like _Aepyornis_ or
> _Dromornis_, but in the smallest living ratites, the kiwis (_Apteryx_
> spp.). Kiwis have the largest eggs relative to body size of any bird
> - I've heard a figure of 25% of the mother's body weight bandied out.
> The amount of yolk per kiwi egg is about the same as that of an emu
> egg. This is according to Calder, W.A. (1979; "The Kiwi and Egg
> Design: Evolution as a Package Deal" BioScience 29: 461-467), who has
> a few ideas on why kiwi eggs are so big.
> The shell of an egg has to be thick enough to resist external stresses
> - not just when being deposited into the nest, but subsequent
> incubation by the bird (i.e., being sat on), as well as being jostled
> inside and against the nest. But the shell has to be thin enough that
> the chick can break out. Kiwi eggs have very thin shells. It is
> thought that the kiwi's underground burrow helps cushion the eggs,
> allowing the eggs to have thinner shells (relative to the volume of
> the egg). Plus, adult kiwis aren't that big - allowing underground
> burrows and nests to be part of their ecology in the first place, and
> meaning that the adult doesn't exert too much pressure on the egg when
> he/she incubates it.
> The egg inside the mother kiwi is so large that it does take up a
> great deal of internal space in the period just before laying.
> Apparently the egg expands at the expense of the stomach, preventing
> eating in the period prior to laying. I don't know if the sheer mass
> of a herbivorous bird the size of _Aepyornis_, _Dromornis_ or
> _Dinornis_ would have allowed the mother to break off from feeding for
> a few days or more.