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

["David Marjanovic" <david.marjanovic@gmx.at>]

----- Original Message -----
From: "John Bois" <jbois@umd5.umd.edu>
Sent: Thursday, October 04, 2001 10:26 PM


> On Wed, 3 Oct 2001, David Marjanovic wrote:
>
> > Now I realize what your basic assumption is: that nonavian dinosaurs
didn't
> > make any attempt to hide their nests but always preferred battle! Right?
:-)
>
> I don't know whose law it is, but it is better to run than to fight.  But
> if dinosaurs ran every time a large predator approached they would never
> reproduce.

So it is not always better to run?

> This put selection on defense, and, I believe, fueled an arms
> race for increasing size.

The problem is that evidence for or against the former is scarce and the
latter is destroyed by *Microraptor*, *Archaeopteryx*, birds and many others
that are supposed to have had bigger or equally sized ancestors, not to
mention that the biggest sauropods are not end-K (and sauropods didn't have
the biggest eggs).

> > If so, it has been falsified with the discoveries of Egg Mountain and
Egg
> > Island -- islands in an alkaline lake where *Maiasaura* nested -- and of
> > apparent colonial nesting in oviraptorids.
>
> On the contrary, colonies are wonderful defensive structures--as long as
> by increasing the numbers of defenders you reduce the probability of
> predation.

OK, but this also works when the predators are mammals or neornitheans. Why
shouldn't it?

> > I should also mention the
> > pterosaurs from Chile that nested in the desert (as some seabirds in the
> > region do today...
>
> Not sure what you mean here.

They fished at sea and nested far away in a desert. Today some seabirds nest
in the Atacama for the same reason. I'll have to dig up a ref, but AFAIK it
was reported on an SVP meeting too.

> Flying creatures

, such as pterosaurs,

> can lay their nests
> remote from many "home predators".

> > Extremely generalizing hypotheses of that sort are generally... oops :-)
>
> 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

known

> late K dinos were larger than
> ostriches (from memory, now).

Longer, taller and/or heavier? (I wouldn't trust estimates on the last.)
Individuals or species? How old is the database?