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>>He seems to be saying [and I agree -
Correct me if I'm wrong, Nathan], that ANY _major_ cause of the extinction (or
multiple causes) will result in the complete extinction of some groups, and the
near-extinction of most of the rest of the groups. (Just speaking about
statistics).<<
I'm uncomfortable with the idea that the cause
of extinction had random effects. Mr. Myhrvold said:
>>It is estimated that whatever caused
the KT extinction killed 90% of extant taxa in all groups in the biosphere (i.e.
land and sea). Whenever you do that, you are bound to kill 100% of some
groups and < 100% of some other groups - purely by random chance.
ANY method that randomly kills 90% of all taxa will cause extinction in some
families and not in others, without any additional explanation because it simply
is random.<<
The problem is the selection mechanism is NOT
random. It presents a certain set of problems, and the taxa that survive
are those best able to cope with those problems because of some advantage,
biological, geographical, or some other. The alternative, random selection
of survivors, is that the mechanism should have killed 100% of taxa, but by
random chance a few individuals were spared. In that case, there would be
an absence of pattern in the survivors. The observation that there
appears to be some pattern in the survivors makes it likely survival was not a
random event.
To clarify, take a
lottery, for example. (You knew I'd get to this.) Any number has an
equal chance to be the number drawn. Given enough outcomes to
discount flukes, you'd be able to demonstrate that the event producing the
numbers was selecting those numbers randomly. That's not the case
here. (Ok, some survivals/extinctions might be random, but I'm speaking in
general.)
In fact, it seems an effort is being made to
use the survivor patterns to discern the outlines of the selection
mechanism. Your discussion of size and hibernation is an example. By
definition, that effort would fail if survival was purely random.
Dismounting from my
hobbyhorse...
----- Original Message -----
Sent: Tuesday, March 21, 2000 12:34
AM
Subject: RE: Extinction
Joao:
I think you are missing some of
the idea behind Nathan's list of reasons. He seems to be saying [and I
agree - Correct me if I'm wrong, Nathan], that ANY _major_ cause of the
extinction (or multiple causes) will result in the complete extinction of some
groups, and the near-extinction of most of the rest of the groups. (Just
speaking about statistics). Also, the bias towards the survival of
smaller animals is very important, especially concerning
dinosaurs.
As to the small dinosaurs, it is
possible that the only surviving small dinosaurs WERE the birds, possibly
due to their greater mobility.
Curiously, I first suggested
hibernation as a potential differentiator in the survivors around 12-13 years
ago, when I was teaching a course about dinosaurs at the Academy of Natural
Sciences of Philadelphia. As Nathan said, hibernation and small size
seem to be the best explanation for the survivors.
If you check back in the Dino List
Archives, you'll see that we've had several detailed discussions on this
topic. Somewhere in my personal collection of these messages, I have a
few long lists as to why I think that the extinction was TRIGGERED by the
impact of something very large. [If I finally recover my old hard drive
(hopefully next week - 'Search & Rescue' has been a god-send!), I have
them stored there - and I can send you a copy of the most complete of
them].
Allan
Edels
OK. And the lesser dinosaurs? Your
arguments are strong, but dinosaurs were a highly polymorphic group. Did
randomic extinction destory all dinosaurs? Why did the birds
survive?
And the plants? Everyone say...meteor
falling...dust.. sunlight blocked...plants die...herbivorous dinosaurs
die...etc
There's some evidence that plants were
affected?
All frogs hibernated? All lizards? All
turtles?
I think still there's much to be discovered.
The records in Southern continents are still so poor. I think S America,
Sotheast Asia, Australia, S Africa and India are the keys to new
findings.
Thanks for the reply
Joao
----- Original Message -----
Sent: Tuesday, March 21, 2000 12:44
AM
Subject: RE: Extinction
There are many arguments about this, but here are
those I find most compelling.
1. It is estimated that whatever
caused the KT extinction killed 90% of extant taxa in all groups in the
biosphere (i.e. land and sea). Whenever you do that, you are bound
to kill 100% of some groups and < 100% of some other groups - purely by
random chance. ANY method that randomly kills 90% of all taxa
will cause extinction in some families and not in others, without any
additional explanation because it simply is random.
2. There seems to have been a
systematic bias against animals of large body mass. So, it was
not a completely random 90% - your odds of survival were greater if you
were smaller.
3. There may be (this is more
controversial) a bias in favor of survival for animals that
hibernate, have a dormant life cycle for part of the year, or
burrow. This includes many small mammals, and it also includes
many frogs and amphibians.
Taken together, these three effects - random
chance that some groups would have some survivors, and a bias against body
size and a bias toward burrowers/hibernators are probably the best
explanation to date.
Note that these arguments are not specific to an
impact scenario - it is the statistical properties of any KT
mechanism that matter.
Nathan
1)Thank you all who answered
me.
2)Nobody can convince me about this
"meteor-destroying-dinosaurs". It's sure there was a meteor impact on
KT, but why it destroyed only dinosaurs, pterosaurs, ammonites and
marine reptiles? Why it did not kill frogs, or turtles? The mystery
continues.
3) Southeast Asia was part of Angara or of
Gondwana?
Joao SL
Rio
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