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Re: Extinction scenarios

At 06:03 PM 8/17/98 -0400, John Bois wrote:
>On Mon, 17 Aug 1998, Betty Cunningham wrote:
>> where are we getting the figures for 100% survival of mammals in
>> Montana?
>Archibald, J.D. 1996 Dinosaur extinction and the end of an era: what the
>fossils say.  Columbia U. Press pp. 126, a graph showing 100% survival of
>eutherians (placentals) over the K/T boundary in Eastern Montana.

Checking the earlier Table 5.1 (pp. 84-85) from which the graph on p. 126 is
derived, one can find that the eutherians concerned comprise only six
species in two families: the gypsonictopid _Gypsonictops illuminatus_ and
the palaeoryctids _Batodon tenuis_, _Cimolestes cerebroides_, _C. incisus_,
_C. magnus_, and _C. propalaeoryctes_.  Of these, all but _G. illuminatus_
are marked as "rare".

It should be noted that while it is fair to say that there is 100%
survivorship of known eutherian species in the Hell Creek into the Tullock
Formation, it is not fair to extrapolate from this 100% survivorship is
necessarily descriptive of all eutherian clades everywhere in the world.  We
know (from Archibald & others work, recently summarized in Dingus & Rowe's
_The Mistaken Extinction_) that many lineages of eutherians beyond the
gypsonictopids and palaeoryctids were present by the end of the Cretaceous.

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:th81@umail.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661