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RE: Dino Demise by Angiosperms



> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> Daniel Bensen
>
> >>(in North America at least) the gymnosperms increase sharply at
> the K/T-boundary (first the fern spike and then conifers replace
> angiosperms as dominant trees). <<
> What was the cause of the spike?  Reaction to a cooler world
> climate?  Is the
> ratio of angiosperms to gymnosperms still at the level it was
> just after the K/T
> extinction, or has the spike in gynosperms gone back down?
>
> Dan
>
>
The fern spike is a western North American phenomenon.  It seems to indicate
the sudden disappearence of FORESTS (both gymnosperms and angiosperms), and
subsequent pioneering of the  by fern "weeds".  The phenomenon represents a
VERY brief event: most likely the larger scale obliteration of forests in
western North America.

A somewhat similar event has been noticed at the Permo-Triassic boundary: in
this case, a marked increase in the amount of sediment in stream deposits in
southern Africa.  This is interpreted as representing the short-term
disappearance of ground cover, so that there is little left to bind the
soil.

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742
http://www.geol.umd.edu/~tholtz/tholtz.htm
http://www.geol.umd.edu/~jmerck/eltsite
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-405-0796