RE: Armadillos at the K/T!

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

On Mon, 1 Oct 2001, Michael de Sosa wrote:

> I'm sure this has been brought up before, but how come dinosaurian
> egg-and-young-eaters didn't wipe out the larger species a hundred million
> years before this? They were above badger-size for a lot longer than the
> mammals were, if that means anything.

They may well have been stressed by birds.  In any case, It seems that by
the end of the Cretaceous non-avian dinosaurs were not competitive
in the small animal niche.  They had put all their eggs in the big animal
niche.  It is likely that they had most to fear from other big dinosaurs
(after all, they were stuck to one site for 3 months or so).  They were
diametrically evolved to be unable to protect themselves against small,
nocturnal, fossorial beasts--there were few to none of these among
dinosaurs).

> Sorry if I seem skeptical before knowing all the facts, but it just seems
> unlikely to me that diverse groups of mammals on every continent waited
> until the very end of the Cretaceous to simultaneously grow large enough to
> be a threat to dinosaur eggs, and that they found and devoured every single
> nest of every single dinosaur species on every single continent. Not to
> mention that this remarkable feat of dietary prowess occurred around the
> same time as a huge meteor hitting the Earth and severe climate changes due
> to regressions in sea level.

We must remember that the extinction of dinosaurs is only recorded in one
place.  I am arguing that mammals and birds contributed there and that
they have had an abiding effect everywhere else in the Cenozoic.
  
> There were probably tons of factors affecting the K/T mass extinction. Nest
> predation may be one of them, even an important one, but I have a hard time
> believing it was the primary one.

Possibly true.  However, the apparent continuing selection against big egg
layers--that is, we see the mechanism in action--should make it a prime
(if not the prime) suspect.