Re:

[Tom Holtz <tholtz@geochange.er.usgs.gov>]

>Perhaps
>Keller is right and what we are looking at is the meteor (or volcanic
>eruption) delivering the coup de gras to a world which had been ecologically
>stressed for hundreds of thousands of years.

Or millions of years.  Both my own data on dinosaurs (sorry) and various
others on rudists, inoceramids, forams, some plant groups, etc.  show a
stepwise extinction pattern on the grand scale, with major lineage
terminations in the Campano-Maastricthian boundary and at the
mid-Maastrichtian.  These stepwise events may be associated with the
Maastrichtian regression (for those of you out there who don't know, the
last 6-8 million years of the Cretaceous were marked by a major draining of
the continental seas).

                                
Thomas R. Holtz, Jr.                                   
tholtz@geochange.er.usgs.gov
Vertebrate Paleontologist in Exile                  Phone:      703-648-5280
U.S. Geological Survey                                FAX:      703-648-5420
Branch of Paleontology & Stratigraphy
MS 970 National Center
Reston, VA  22092
U.S.A.