Re: Armadillos at the K/T! (long)

[Graydon <graydon@dsl.ca>]

On Thu, Oct 04, 2001 at 04:26:35PM -0400, John Bois scripsit:
> That's true, generally.  But Late Cretaceous dinosaurs were united by many
> similar imperatives.  According to the data I have been able to access
> (Graham Worth's data base) over 90% of late K dinos were larger than
> ostriches (from memory, now).  Meaning...they found it more difficult to
> hide than smaller species (a mountain is easier to find than a pebble).

But they don't have to hide *them*; they have to hide the *eggs*.  If
the adults are large, they've got a couple of alternatives not
available to current ratites -- nest materials small predators can't
move, and massive nests -- as well.  Maisauria nests were substantial
excavations, in heavy clay or fine mud, materials that a mammal would
have trouble tunnelling through, and getting to the nesting ground
involved crossing the alkali lake.  As passive defenses, that looks
pretty good against small mammalian nest raiders; the general location
of the nest may be obvious, but getting into any particular nest for the
eggs will be hard.

Predators will be selected for relative success, as well; if it's easier
to eat hatchlings than eggs, that's what the predators will tend to try
for.  If the hatchlings are easier to defend, that's a net win for the
parents.  (hatchlings can at least run away, which has to help some...)

Small dinosaurian predators still have to dig into the nest -- something
the usual small theropod is ill-suited to do -- and avoid the adults.
Large dinosaurian ones would rather eat the adults.  It doesn't look
like a particularly tough situation for a large R strategist.  There are
going to be losses -- there had better be, given the implied breeding
potential! -- but it's not at all obvious how egg-and-hatchling
predation is going to be overwhelming under those circumstances, any
more than it's obvious how it's easy to grab buffalo calves out of the
herd.  (It happens; it happens quite a lot.  But it's not easy for the
predators, and the herd doesn't tend to shrink.)

-- 
                           graydon@dsl.ca
               To maintain the end is to uphold the means.