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Re: Nesting with Dinosaurs.




On Tue, 18 Apr 2000, Larry Dunn wrote:

> --- John Bois <jbois@umd5.umd.edu> wrote:
> > As in: "Many of the events portrayed in this
> > show are speculative.  For example, though there is
> > no direct evidence for
> > what killed the dinosaurs, the bolide makes a great
> > story."
> 
> And, "there is no direct evidence that mammals raided
> dinosaur nests and ate their eggs."
 
Very good and touche.  But, then again, we know extant mammals do
this.  We know that wherever there is a large egg being laid, in
almost every case, there is a mammalian predator.  Mammals desire
eggs.  The question is not one of will, more of ability.  So, we can make
a reasonable speculation that this may well have occurred.  Regarding
bolide, the trouble is that NO REASONABLE SPECULATION HAS BEEN
OFFERED.  Rather, we are expected to believe  that the dinos were just
kind of blown away by quivers full of cataclysmic events.

Actually, the show is a bit of a breakthrough in the egg domain.  At last
we can visualize nest predation where gape is not an issue.  As you know
the dominant predators on large extant dinosaurs (rhea and ostrich) have
mouths incapable of breaking eggs.  But this is no impediment.  They
simply knock them together.  Yet gape is subject to misconception even by
the wisest of researchers.  For example, Kenneth Carpenter, in his
otherwise fantastic book (a must read, in my view) cannot consider mammals
as a potential cause of extinction because, "(considering) the small size
of their mouths, it seems doubtful that any of these could have cracked
open a dinosaur egg."  He does, however, think _Didelphodon_ may have been
capable of this.

Tom Holtz' comments on the raiding of an abandoned nest are
appropriate.  Yet, why must our speculation stop there.  My leader, Mickey
Rowe, argues well in Paleologica paper, that many/most dinosaurs may have
been diurnal.  If they had poor night vision they would have been at the
mercy of egg robbers, who they couldn't see.  Here again we see a modern
analogue: black-backed jackals cannot steal ostrich eggs in day time but
do so without penalty at night!  Further, given the size relative to their
offspring--both eggs and hatchlings--there would likely be a strong
inhibition to nocturnal movement.  I don't see that _T. rex_ has an answer
once mammals reach some threshold of size and/or behavior.

So, for a final piece of speculation, I propose a sequence for this (in
North America, at least).  Mammals (in cahoots with birds) reach some
behavioral threshold in small dinosaur niche and drive them into
extinction.  Once these mini-tyrants are gone, selection on small
size of mammals (for stealth) has been relaxed.  Mammal size can increase
to the point that they can handle bigger eggs.