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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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