Re: Triceratops defence

[John Bois <jbois@umd5.umd.edu>]

On Sun, 13 Jun 1999, Ronald Orenstein wrote:

> Perhaps it was as you say
> - or perhaps the eggs were carefully hidden somewhere - we don't know -
> possibly with different parts of the clutch in separate places.

So this is where I'm claiming at least a teensy bit more leeway should be
granted; that there
are factors which make this highly unlikely.  Such as: It would be
difficult for a triceratops to lay and leave.  They couldn't swim to a far
off island, like sea turtles.  They couldn't slither down a hole like
lizards and snakes.  They couldn't creep away unobserved and hide the egg
under a rock.  When they go somewhere, they leave a large signature, a
signal for predators.  If they had growth rates anything like avian
species (there is support for this, isn't there?) they couldn't bury the
eggs anywhere and leave them to develop on their own.  Hole-nesting
megapodes are one of the few species that do this.  But triceratops eggs
would be limited in this respect.  Firstly, with larger eggs their surface
area/volume ratio was smaller making burial problematic for O2 diffusion.
Secondly, rapid developmental rates require very consistent
microenvironmental optima--but near surface burial would mean temperature
swings (diurnal, at least), and therefore slower incubation rates.
Well, anyway, I'm trying to argue that maybe we aren't there yet, but that
there are other ways than just fossils to get at these questions.

> Until
> someone finds fossil evidence we are only assuming.  Of course there is the
> (perhaps remote) possibility that they gave birth to live young that were
> active soon after birth, like zebras or elephants today - if this was the
> case it could have been a useful adaptation for the animals if they were
> continuously on the move.  Again, we just don't know. 

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.  J. David Ligon, in The evol of avian breeding systems, Oxford
U Press 1999, claims that this is simply because ovipary, for birds at
least and nothing to do with flight, is superior.  He says bi-parental
care is a winning factor here, among other things.

But I certainly accept your points about the details of any defensive
strategies.