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Re: K-T selection event



jamolnar@juno.com wrote:

<snip>
> 
> You're not the only one who feels this way!  The problem is, the
> extinction was very selective, and yet there doesn't seem to be an array
> of consistent traits in the survivors.  Plus, people are still tallying
> the survivors.

Which is a big reason why I think there's still a missing element.  For
a hundred years people have been trying to find a single coherent
explanation for the K-T extinction, land, sea, and air, and no one has
ever managed it.  To me, that indicates a strong possibility that we're
asking the wrong question -- that we can't find one cause for _all_ the
extinctions because they didn't all have the same cause.  Maybe
dinosaurs got the chop because of some massive upheaval in land
ecosystems, while marine groups got taken out for different reasons. 
Ammonites pose the least mystery of all -- they'd gone through mass
extinctions several times in the Mesozoic, and in at least one of those
cases they were down to just two or three genera.

> One idea for the land critters might be that there were climactic
> extremes that would take out large animals of intermediate metabolism.
> Aridity was increasing, there was intense global volcanism, global sea
> levels were falling, and the inland seaway in North America disappeared.
> This could have made for more seasonal swings in temperatures and
> rainfall.  The low metabolism animals could hibernate through the crisis,
> the high metabolism animals could migrate away quickly to refuges.  Maybe
> the "in betweeners" couldn't do either of these effectively.  

I've not heard of high-metabolism mammals like shrews and mice being
able to hibernate or migrate real well.  

> Another idea I've seen is that small animals, birds and mammals could
> find refuges from the acid rain from the volcanism, and dinosaurs may
> have had sensitive skin.  But that wouldn't explain why many amphibians
> survived (most of which are acid sensitive and dependent on freshwater).

Maybe whatever was raining was rendered harmless by freshwater?  Or
maybe the rain wasn't acidic but alkaline?

> But my problem with all of these musings is that we can't just ignore the
> extinctions in the air and the sea.  There was so many extinctions going
> on all over, we can't just focus on one set of ecosystems and ignore the
> rest, because they are all linked.  

Are they?  I'm not so sure of that.  It seems like an obvious
conclusion: all the extinctions happened at about the same time,
therefore they have a mutual cause.  It's almost too obvious, in fact. 
In keeping with Murphy's ninth law (in any collection of data and/or
ideas, the one that seems most obviously right is the one most likely to
be wrong <g>), I keep thinking that throwing out that conclusion could
lead to some new and productive approaches to the problem.

-- JSW