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Re: [crpntr@ix.netcom.com: Re: Walking with dinosaurs]




On Thu, 20 Apr 2000, Mickey Rowe wrote:
Kenneth Carpenter wrote:

>   Thanks for the kind words on my book. Regarding the mouth size, you
>   must understand that MOST carnivorous mammals were the size of a
>   shrew, hence would barely be able to get their mouth around your
>   pinky.

I agree.  But most large egg layers today
are only preyed on by a couple of mammalian predators.  Indeed, in the
case of rheas a single predator causes very high mortality.  

>  In addition, the teeth are all very high cusped, as in a
>   shrew, and indicate a diet of insects. A shrew-size mammal cannot
>   push a navel orange-size egg (the average size of dinosaur eggs)
>   against another to break it open, let alone get its mouth around
>   it.

Yes.  And I'm not proposing that shrew-sized mammals did the damage.

>   However, Gobicodon and Didelphodon, cat-size, could easily crack
>   open snaller eggs or ends of eggs in their mouth (e.g., the end of a
>   Elongatoolithus egg).

 ...and _Cimolestes magnus_ (badger-size, I think), and possible
undiscovered candidates (we haven't found the ancestor of first
known Carnivora--found in earliest Paleocene).  In my view there is some
relaxation on size selection going on.  What about that huge
(dog-size) multi (Taeniobilis, I think it's called) sitting in the
Smithsonian?  I'm not suggesting its rodent-like
teeth were good for cracking eggs.  I am suggesting there was a shift to
larger size toward the end of the Cretaceous.  

>   I don't think that rolling eggs together to
>   break them open was a very important strategy because dinosaurs
>   apparently buried their eggs. Ostrich eggs that get broken by
>   banging against another are laid in the open where there is no
>   constraining earth to keep the eggs from rolling. That then leaves
>   only the mouth as a way of breaking open an egg.

Yes, that's exactly what I thought until I wrote to researchers on Rhea
predation.  They think the only way the diminuitive Hairy armadillo can
get into an egg is by this method--their mouth is way too small to gain
purchase.  When they create a network of tunnels beneath the nest, it
collapses under the bird's weight.  Down come the eggs, undoubtedly with
alot of soil.  Still they manage.  Reboreda believes they must knock the
eggs together.  Perhaps it is possible to dig the soil away from two eggs
and ram them together.  A mystery to follow, for sure.

Thanks for the response.
John Bois.