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re:K/T boundary in TX



John Alroy, et al.:

     I received, via Mickey Rowe, a transcribed version of Dr.
Ralph Chapmans appeal for closure on this K/T extinction debate
(I was temporarily unsubscribed when it was sent):  I agree that
we've reached an impasse where much of the discourse is on skewed
planes.  Just a minor technical point, of probably limited
controversy, to which I wish to respond:
                   ____________________


>>>>"In other words, unless the K-T is misplaced in this section,
there IS no gap at all between the Ir spike and the last
occurrence of dinosaurs. So much for the "gap" theory, unless, of
course, you want to argue about the number of centimeteres WITHIN
this paleosol that separate the dinos and the....."<<<<

Perhaps I'm out of touch, but I never claimed that non-avian
dinosaur remains disappear any distance stratigraphically below
the K/T boundary anywhere they are found. I'm not sure anyone
claims such. What is evident is that their *diversity* drops in
the later Maastrichtian and the *apparent population density*
(reflected in rare fossils) drops a meter or so below the
apparent boundary.  As we all have acknowledged, there are even
reworked dinosaur bones and teeth in Montana Tertiary channel
deposits: therefore, it is imposssible to claim absolute
disappearance at any point in the Maastrichtian since we cannot
know from which horizon these were originally derived.

pace,

David Schwimmer
schwimm@uscn.cc.uga.edu