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Re: Twighlight zone for dinosaurs.



No takers?  The creatures involved are the hairy armadillo preying on rhea
eggs.  I quote this remarkable behavior from Fernandez, G.J. and J.C
Reboreda 1998 _Effects of clutch size and timing of breeding on
reproductive success of Greater Rheas_ The Auk 115(2):340-348.

"Rainfall could have affected nest desertion directly as a consequence of
flooding, or indirectly by increasing the probability of nest predation by
armadillos or other predators.  Hairy armadillos create a gallery of
burrows that converges at the base of the nest and from which they steal
the eggs.  The nest is usually destroyed (literally, it sinks), and the
male rhea deserts.  In years of high rainfall, male rheas nest in the
higher areas where armadillos are more abundant.  In contrast, in years of
low rainfall, males nest at places that normally are flooded and where
armadillos are absent.  These places also have higher cover such that
nests are less easily detected by other nest predators."

The armadillo is about 40-50 cms long (from snout to tail) thus putting it
in range of Cretaceous mammals.  Such a model for potential cretaceous
mammalian nest predation has been previously (to my knowledge) absent.
This may not have anything to do with dinosaur extinction.  Rather, it
gives a horrific glimpse into how they might have struggled to survive!
Rhea catch it coming and going (by the way, the authors note predation on
their nest was probably significantly less today than in the past due to
major predators being extirpated from its range).  After chicks hatch they
are preyed upon by caracara birds of prey.  The upshot is that only 1 in
10 embryos reach 3 months old because of these important factors.  One can
only imagine what nest life was like when non-avian carnivores were
around!

Also interesting from a science process standpoint is the following:  I
had read Donald Bruning's Rhea papers and found it saddening that he made
no mention of any egg predation whatsoever.  So I e-mailed him and asked
him if this was an omission.  He replied, no, and that he believed mammals
simply couldn't get into the large very hard-shelled eggs.  That was that.
Then comes this paper reporting an apparently time-honored practice of
these armadillos.  I don't doubt the validity of Bruning's original
research.  But it does point out the danger in making assumptions from a
single series of observations, or single locality (and I certainly did
make that assumption).

Another conclusion I would like to make is that an animal's gape has
nothing to do with its ability to gnaw into a hard-shelled egg.  But I
can't.  I don't know how the armadillo get into the egg.  For all I know
they might roll them together (though this would seem difficult in the
collapsed nest and dirt matrix) as the black-backed jackal does an
ostrich's egg.  I will e-mail the authors and get back (assuming they
know).

Finally, I realise the timing of my discovery was unfortunate.  Some
thought I was trying to tweak the nose of the extinction moratorium.  This
information has definite non-extinction relevance and as such should not
fall under this ban.  I admit that much of what I talk about has the
extinction as a subtext.  However, as long as I can be trusted to not drag
the list into such a discussion--and I have _no_ desire to do this--I feel
I should be tolerated as long the subject is not extinction _per se_.

On the other hand, it is not fair to suffer insults without being able to
respond to them--for I am always able and willing and evermore capable of
doing so.  In that vein I would like to advise Larry that it is not the
_stealthy egg idea_, it is the NON-stealthy egg idea.  And it is not sung
to the tune of William Tell.  It is sung to the tune of the Macarena.