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

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

----- Original Message -----
From: "John Bois" <jbois@umd5.umd.edu>
Sent: Friday, October 05, 2001 7:06 PM


> On Fri, 5 Oct 2001, David Marjanovic wrote:
> [...]
> > So it is not always better to run?
>
> If you are a mammal and face a predator who has a better than even chance
> of besting you, it is always better to run.  But baby runs with you
> because either he is fast himself [...],

Same for precocial dinosaurs.

> or he is still inside mummy.

In this case he represents a burden for mummy who's therefore more likely to
die which means the death of both. Bad for a K-strategist. Kangaroos
sometimes throw their baby out of the pouch which means its death but the
mother's survival, and a reserve embryo is already in storage.

> Thse
> choices are not as clear cut for a dinosaur who must weigh the destruction
> of his brood if he abandons the nest to reproduce another day.

Then he does reproduce another day -- r-strategy!
What about buried nests? Not everything can dig fast enough to get at buried
eggs before a parent returns.

> Some speculation is better than other speculation.  The speculation that
> large dinosaurs were hard to hide and, therefore, had to defend their
> nest, is a pretty good one, in my view.

Large dinosaurs were harder to hide than small ones. Not necessarily their
nests.
Don't you think it's possible to defend one's nest against a mammal? :->

> >...and
> >the
> > latter is destroyed by *Microraptor*, *Archaeopteryx*, birds...
>
> No.  Small things can hide.

The "arms race for increasing size" is disproved by it.

> They thus avoid the hazard of obligatory
> defense.

First show me this is a hazard!

> So, the hypothesis depends upon dinosaurs being big--which,
> curse me, is the same assumption for the bolide idea.

No. The bolide idea states that everything terrestrial above 25 kg will die
because of the sheer earthquake, at least close to ground zero, and that
_most_ below 25 kg will _likewise_ die out. Which is what happened =8-)

> For example if the David dinosaur was being attacked by
> a _T. rex_, a John dinosaur nesting next to him would also be
> threatened.  I would join the fight.

Pretty useless if you're a hadrosaur (and not, say, a *Triceratops*). Your
nest should survive when you run away unless *T. rex* tramples it, if the
young are precocial enough or if you come back.

> If, though, your nest was a seething
> mass of furballs,

Ah, that's your assumption -- _incredibly vast numbers_ of big mammals
suddenly coming from nowhere! That's really bad speculation. Recent
mammalian (or other) nest robbers tend to come alone AFAIK, and there simply
aren't "seething masses" of them.

> > 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.
>
> Yes, nesting in remote places is a great idea.  Not to say the dinos
> didn't do it, just that they were less effective at distancing themselves
> >from other walking dinosaurs.

I just say _pterosaurs_ did it and should therefore have survived according
to your speculations.

> > > 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?
>
> I looked through Worth's database (3.0) again.  The vast majority
> of Late Cretaceous species were over 4 meters in body length.  I'll try
> and get a better figure.

I'd really like to know which year this database is from.
I haven't counted, but when I look at the list of "Dinosaurs of Alberta by
Formation, Exclusive of Aves" on p. 288f. of Mesozoic Vertebrate Life, I get
very different estimates (around or below 50 %).