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Re: Response to Nick Pharris: Patterns

From: Thomas_R_HOLTZ@umail.umd.edu (th81)

 > While this is likely, it is not certain.  _Purrusaurus_, an
 > alligatorid as large or larger than any of the Cretaceous crocs, is
 > from the Miocene of Amazonia, where the largest prey items were 3 m
 > long fish, ...

And among the survivors of the K-T transition in the Hell Creek
area were some of the largest freshwater fish in existance -
fish whose descendents can still be found in the Missouri-Mississippi
river system: sturgeon, pike, bowfin (I mean Amia).  I rather think
even fairly large crocs could manage on sturgeon.

 > Which was long extinct at the K-T boundary.  Why would a _Troodon_
 > or a small hypsilophodont nest be so hard to conceal?  Surely one of
 > these little guys could hide under the brush.

And very likely did so.

 > Also, as stated before, there is no evidence that Mesozoic birds were
 > tree-nesters.

I would venture many were island and/or wetland nesters, however.

 > Actually, some Mesozoic mammals DID have to consider this, since
 > some (the ancestors of monotremes, and possibly all taxa up to the
 > metathere-euthere divergence) were egg layers.

Probably including the abundant and diverse Multituberculates, which
survived quite well until the Eocene.

 > Not directly, actually.  There is abundant evidence that extinctions
 > are correlated with times of climate (and thus habitat) fluctuation.
 > In the case of modern extinctions, however, the ultrapredation of
 > humans does seem to be a major factor.

Not in all of them.  Stephen Gould has written about one (obscure)
recent extinction that was apparently unrelated to human activity.

It was exacly as you say - it was due to environmental fluctuation.
In particular a run of unusual weather in the are where this snail
lived eliminated its narrow habitat temporarily. Bing - its gone.
No predation involved. This mode of extinction is probably a major
one in the absence of oddities like humans.

swf@elsegundoca.attgis.com              sarima@netcom.com

The peace of God be with you.