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Re: _Night Comes to the Cretaceous_



Dinogeorge@aol.com wrote:

> In a message dated 98-08-08 07:18:53 EDT, jwoolf@erinet.com writes:
>
> << There is nothing all that strange about a mass extinction, if you
> understand
>  ecological dynamics.  It's entirely possible for one element to get out of
>  alignment and have a massive destabilizing effect.  An unstable ecosystem is
> a
>  vulnerable ecosystem, and it can fall apart in a shockingly short amount of
>  time.>>
>
> You're still talking about local effects here. The world comprises hundreds or
> thousands of ecosystems.

Each of which can break down for a different reason.  And ecosystems don't exist
in isolation -- when one breaks down, its neighbors are also affected.  Woodland
ecosystems affect edge ones; edge ecosystems affect grassland ones; land
ecosystems affect water ones; et cetera.  Engineers call it a "cascade failure."

> <<If something wipes out the top predator, for example, unpreyed herbivores
>  can strip the land bare and eat themselves into starvation.>>
>
> How would the disappearance of, say, _Tyrannosaurus rex_ in North America
> affect the herbivorous dinosaurs of, say, India?

It would matter if the same or closely related species is the top predator in 
both
places, and a sweeping pandemic or other external cause kills it both places.

> <<  Or if a new type of plant appears which spreads rapidly and which none of
> the big herbivores can eat -- kudzu or spurge, for example. Or a fungus or
> microbe that parasitizes a large array of species like _Pfiesteria_, the
> infamous "cell from hell" that has been ravaging the fish populations along
> several parts of the East Coast every year for several years now. >>
>
> How would the appearance of kudzu in, say, South Carolina, cause the
> extinction of, say, bald eagles in Alaska? Kudzu arrived from somewhere else;
> why isn't the place it arrived from devastated?

Because in the place where it was -- East Asia, if I recall correctly -- it was
controlled either by climate or by local herbivores.  Suppose a new species of
plant arose that had no enemies in its origin-place and spread from there?  Yes,
eventually something would turn up that could eat it, but in the meantime it 
could
do a heckuva lot of damage.

> Global mass extinctions >must< have global causes.

But not necessarily _extraterrestrial_ causes.  Maybe everything traces back to
global climate -- it looks like a brief burst of global warming was instrumental
in the Permian extinction.

> And--which "evidence" does the asteroid/comet impact at the K-T
> boundary not "explain"? If you do indeed have evidence that the impact
> >didn't< cause the K-T mass extinction, trot it out. Maybe it's publishable.

I know it's published, because it's all _been_ published by people with
credentials.  All the versions of the impact theory that I've seen fail to
explain:

* the lack of extinction among small endotherms.  Small endotherms MUST have a 
lot
of food intake to stay alive and keep their metabolism going.  A shrew can 
starve
in a few hours, a small bird like a warbler can starve in a few days.  The 
impact
scenario does not explain where these animals continued to find enough food, 
when
plants were wiped out or had their growth badly stunted by the cold and darkness
of the 'asteroid winter.'

* the fact that even cold-weather, high-latitude dinosaurs disappeared.

* the marine extinctions.  Why mosasaurs and not crocodiles?  Why plesiosaurs 
and
not sharks?

* the aerial extinctions.  Why pterosaurs and not birds?

* the fact that _every_ dinosaur other than birds disappeared.  Small ones, 
large
ones, tall ones, short ones, herbivores, carnivores, insectivores, they were 
wiped
out to the last individual.  Champsosaurs were as big as small dinosaurs.  Crocs
were as big as medium or larger size dinosaurs.  Why did they survive where the
dinosaurs didn't?  No answer for that in the asteroid scenario.

* the fact that North American ecosystems did manage to survive, albeit without
dinosaurs.  The impact firestorm allegedly swept all across North America, 
cooking
animals in their tracks and turning trees to carbonized skeletons.  Yet studies
show a continuous fossil record across the K-T boundary in northeastern Montana.
There's no hiatus that could represent the dead zone, before the region was
repopulated by migrants from elsewhere.

* the high rate of survival among amphibians.  "Asteroid winter" should hit
ectotherms heavily, because it deprives them of the sunlight they need for
warmth.  Yet frogs and salamanders, which no one has ever accused of being
anything but ectothermic, did better than endothermic dinosaurs across the K-T
extinction.

* There are no known dinosaur bonebeds at or above the iridium layer.  Surely,
_somewhere_ there must have been a few herds of herbivores that dropped dead in
situations conducive to fossilization.

* the fact that the ammonoid cephalopods, one of the extinction's major victims,
had _nearly_ vanished several times before, but survived in only a handful of
species.  There's no need to invoke an impact to explain their disappearance.

-- Jon W.