Re: Armadillos at the K/T!

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

On Sun, 30 Sep 2001, David Marjanovic wrote:

> OK, but you assume such a case of background extinction for not one species,
> or maybe 10 around the globe, but hundreds or thousands at the same time
> while nothing such happened during a long time before. 

The notion of "background extinction" is specious.  There are reasons for
organisms becoming extinct.  I have suggested what I believe are
potentially good reasons for the extinction of large oviparous
species--reasons which are given more weight by their apparent continuing
operation in the Cenozoic.  It either happened that way, or it
didn't.  Apparent rates of extinction have no theoretical grounding: to me
it is absurd to suggest that extinctions are basically two
flavors--background or catastrophic.  The evidence for terrestrial
vertebrates at the K/T in the Western Interior is neither.

> > Thirdly, while it makes good sense, predator/prey
> >  oscillations around theoretical carrying capacity is illusive to test,
> and I
> >  know of no study which shows this to be the case.
> 
> I'm sure such studies exist. In school I had an example of an island in a
> Canadian lake which was first populated by moose (in a severe winter, over
> the ice); this population exploded and then crashed a few times. Later
> wolves came in, but their population exploded only once (and much less
> extremely), and then the famous fluctuations began.

As I said, it makes good sense to me.  However, the idea that all
organisms are happily oscilating for eternity around a comfy carrying
capacity is romantic.

> > >We have used the bolide hypothesis to
> > >suggest that catalyst to many disrupted ecologies from the Devonian on.
> > > There is evidence for
> > >this.
> >
> >  Evidence of impacts, yes.  None for direct causation, however.
> 
> Now come on. We can be 100 % certain that more than nothing will happen when
> a 12-km-rock impacts aka 10,000 times all nuclear weapons of the world are
> ignited at the same time on the same spot (without the effects of
> radioactivity). It just _can't_ have left all non-neornithean dinosaurs
> unaffected.

I don't think the hypothesis does a good job of explaining 100% of the
extinctions.  I never have (I first heard of it when a student of Gould's
came into class and proceeded to inform us of what was to her a fact--it
just seems more complex to me than that, and I was irritated by the
presumption of certitude wrought from a time so distant--she and Gould,
could have used some humility, in my view, when confronted with a problem
as ecologically complex as this one).

> >  Millions of species have become extinct over geological time.  We have a
> >  fair idea of the causes of only a handful.  How can one claim extinction
> is
> >  _never_ due to predation on young.
> 
> True.
> But to claim _mass_ extinction is due to predation on young is <looking for
> the right adjective...> erm, bizarre.

I'm only claiming that a niche disappeared: that of terrestrial large
oviparous species.  I would like to decouple other extinctions.

> > This is especially difficult to argue
> >  when we realize that by far the most severe cause of mortality in many if
> >  not most species is _predation on the young_.
> 
> Of mortality, maybe (in crocodiles it's AFAIK flooding of the eggs). Of
> extinction?

First comes mortality, then extinction.  Right?  If extant organisms
suffer much mortality due to a certain factor, that factor should be
suspect if extinction occurs.

> > Also, "natural ecologies" are
> >  the denumen of all previous struggles for survival.  Species that
> couldn't
> >  cope are gone!
> 
> So why don't we see progress in evolution?

Greater computational power in most vertebrates relative to Triassic
species.  Ditto speed.  Reproductive security and specialized nutritional
structures in mammals vs. "stem reptiles".  Ability to engage specialized
vectors to carry your sperm in flowering plants.  Independence from water
in plants and animals.  I mean, I could go on forever.  From which planet
must a visitor come that doesn't see these as progressions of a
kind?  The eye.  Birds' wings. etc., etc.

> > Badger-size is a threshold under (or around) which many offspring
> > predators of today operate: hairy armadillo, caracara hawk, coatis,
> > monitor lizards, skunks, squirrels, cats, rats, weasels, foxes...I could
> > go on.
> 
> Nile monitors (famous for eating croc eggs) are AFAIK bigger... However,
> where's the devastating effect of *Gobiconodon* all over Asia and North
> America in the EK? (Just in case >:-> -- it was too early to have caused the
> Cenomanian-Turonian event, which was AFAIK a more marine affair)

You may be right about the monitor--I know it's longer, I would guess less
massive???  What sort of a mammal was Gobiconodon--ecological role,
etc?