----- Original Message -----
Sent: Tuesday, March 21, 2000 12:44
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
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
that these arguments are not specific to an impact scenario - it is the
statistical properties of any KT mechanism that matter.
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
3) Southeast Asia was part of Angara or of