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Re: Extinction scenarios



At 02:06 PM 8/18/98 -0400, John Bois wrote:

>> 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.
>
>But I think it _is_ fair to say that the world-wide adaptive radiation of
>placentals began in the late Cretaceous and continued (amplified on into
>the Tertiary.

I would agree with that: at least in terms of phylogeny, many of the
placental lineages found in the early Tertiary were already extant by the
Late Cretaceous (although they may not have yet acquired all the
characteristics later found in their Cenozoic representatives).

>This point, while not necessarily condemning the
>bolide-as-sufficient idea, is not a friend to it.

Actually, it is totally neutral to it.

>By the way, how would a paleontologist justify Archibald's data with the
>following favorite of mine (in Benton's Vert. Pal. text 1997 but from
>Sloan and Van Valen 1986):

[data clipped].

>I'm just reading these of a non-gridded graph.  But the trend is accurate.
>I'm assuming since Benton put it into his latest edition that the data is
>still valid.

Well, that's not always a safe assumption, since Benton covers his tail by
giving the original citation.  The way to check to see if its safe is to go
back to Sloan et al. (1986) and recheck what changes and additions have been
made to the data in the last twelve years.

For those interested, the reference is:

Sloan, R.E., J.K. Rigby, Jr., L.M. Van Valen & D. Gabriel. 1986. Gradual
dinosaur extinction and simultaneous ungulate radiation in the Hell Creek
Formation.  Science 232: 629-633.

I have to admit, it's been a few years since I've looked at that paper.  As
I recall, the "mammal" data are only for basal ungulates ("condylarths").

The more recent work by Archibald & Bryant (1990. GSA Spec. Paper 247:
549-562)), Archibald (1996, the aforementioned book _Dinosaur Extinction and
the End of an Era_), Sheehan et al. (1991. Science 254: 835-839), Sheehan &
Fastovsky (1992. Geology 20: 556-560), and Hulbert & Archibald (1995.
Geology 23: 881-884) include more recent data than the Sloan et al. paper.

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