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Re: Dinosaur Extinction (Again
John Bois wrote...
> My initial challenge was for someone to match extinction hypotheses with
> the known terrestrial data. I'm not even claiming it can be done. But
> what I am saying is that so far describing the weather at the time, or
> the sea level, or even the cosmic visitors doesn't begin to explain it.
Why not? And why does your single aggravating factor carry MORE
weight, in terms of either evidence or the impact it wpuld have, than global
climate changes or an asteroid impact in causing extinction?
> ammonites died out but vertebrates survived relatively well.
Some vertebrates did. So did most invertebrates. I don't THINK there
is any evidence that K-T extinction was generally speaking especially
favorable toward either vertebrates or invertebrates. The vertebrate
extinctions are just more famous.
And in any case, you seem to think that the fact that dinosaurs went
extinct means there was a HUGE difference in the number of
dinosaur species that went extinct and the number of other vertebrate
species that went extinct. The dinosaurs may have thier numbers
reduced just a LITTLE bit more than other groups, and that was the
difference between recovery and extinction. An environmental aggravation
like an epidemic or disease does not have to kill ALL the memebers of a
species to make it go extinct. If numbers are reduced enough, the a
second peice of bad luck may wipe out the survivors, or they may just be
so reduced in terms of numbers and genetic diversity to recover. The
dinosaurs may have just squeaked a little bit farther across the safetly
line than other vertebrates. So what if most vertebrates survived? They
were all HIT. By what? Coming up with a bunch of global coincidences
that effect a huge number of organisms at once is child's play compared
to coming up with completely different sets of concidences to make a
bunch of different organisms all get hit at the same time. Its even
more concidental consdiering they all occurred ABOUT the same time.
The point is:
1) The dinosaurs weren't the only vertebrate group to go extinct.
2) Most of the groups that survived seem to have had at least SOME
reduction in thier numbers at the same time.
3) I don't THINK there is any evidence that invertebrates, either
terrestrial or marine, were hit less or more severly than vertebrates
as a whole. Some went extinct, some didn't (I'm talking in terms of
PERCENTAGES to all invertebrates: I'd expect that the TOTAL number of
invertebrate species to die was greater than for vertrates, just because
they are more common, but I don't really know what I'm talking about.
The point being that global changes crossing ecological and
environmental boundries are NEEDED to adequately explain most mass
extinctions, including the K-T extinction.
How quickly and abrubtly did climate change start to move during the
Maastrichtian? A world-wide cliamte shift could temporaily leave a LOT,
maybee even ALL species vulnerable until they adapted a little bit. That
would be a really bad time to get hit with an asteroid.