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RE: Theories on the extinction of dinosaurs



> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> Dave Hardenbrook
>
> >My personal opinion is that each contributed significantly to change the
> >climatic patterns, which combined with other ecological pressures
> >(alteration in the dominant flora, mammalian expansion etc.) to make the
> >latter half of  the Cretaceous a pretty damn difficult time to be alive.
>
> I know there is widely believed to have been a decline in dinosaur
> diversity before the _coup de grace_, but it wasn't for the whole
> *latter half* of the Cretaceous was it?

Correct: it was not for the whole latter half of the Cretaceous.  (As a
reminder to folks, the Cretaceous is longer than the whole of the Cenozoic
Era!).

Arguments for a decline in dinosaurian diversity largely concern shifts in
lineage diversity from the mid-to-late Campanian (around 81-71 Ma) to the
late Maastrichtian (68-65 Ma).  This is all at the tail end of the
Cretaceous.

> Besides, wasn't there a similar ecological crisis that wiped
> out many species at the end of the Jurassic?  (The dinosaurs --
> even the non-flying ones -- weathered *that* storm okay.)
>
It is true that all Period boundaries are based on extinctions (of marine
inverts).  In fact, as you mention, dinosaurs surived the J-K boundary fine.
Despite commentary to the contrary, essentially every suprageneric clade
(including traditional "families") of dinosaurs present in the Morrison or
Tendaguru is also found in the early part of the Early Cretaceous.

                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