Re: Triceratops defence

[Ronald Orenstein <ornstn@home.com>]

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
>viviparous.  

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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