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Re: Triceratops defence
John Bois wrote:
>I think we do know this. A placenta-less viviparous species cannot carry
>large babies. How would they get their oxygen? If the babies weren't
>large they were probably, almost certainly, prone to high predation rates,
>especially if undefended.
>It is interesting in this context to note that no avian species are
That is why I said that the likelihood of viviparous dinosaurs was remote -
but note two things: first, viviparous animals, even large ones, do not
necessarily give birth to large young (eg kangaroos and bears), and
non-placental viviparous species CAN produce reasonably large young (up to
70 cm in a tiger shark, for example). Viviparous sharks have quite a range
of adaptations for supplying nutrients to young without a placenta.
Besides, of course, we know that ichthyosaurs gave birth to quite
respectably-sized live young.
It has been suggested, BTW, that birds, because of the nature of their
egg-production process, are evolutionarily foreclosed from developing
vivipary. I am not sure how I feel about this one way or the other, but of
course even if this is true it does not necessarily mean that ornithischian
dinosaurs were under similar constraints.
Ronald I. Orenstein Phone: (905) 820-7886
International Wildlife Coalition Fax/Modem: (905) 569-0116
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