RE: Extinction

["Thomas R. Holtz, Jr." <tholtz@geol.umd.edu>]

An important reference on non-avian dinosaur extinction in the western U.S.:

Lillegraven, J.A. & J.J. Eberle.  1999.  Vertebrate faunal changes through
Lancian and Puercan time in southern Wyoming.  Journal of Paleontology 73:
691-710.

An update of the actual observed fossil record near the K/T boundary.  The
diversity of Lancian verts (including non-avian dinos) remains very high
until right up to the boundary: there are bones and teeth of dromaeosaurs,
ornithomimids, tyrannosaurs, thescelosaurs, hadrosaurs, ceratopsines, and
ankylosaurs in the stratigraphically highest fossil-bearing layers in the
Cretaceous part of the Ferris Formation.  The "missing meter problem" of the
1980s (really a non-issue at the time anyway) is even less of a problem then
before.

HOWEVER, on the flip side, there remains the observation that many clades of
typical Campanian and early Maastrichtian dinosaurs (centrosaurines,
lambeosaurines, etc.) have yet to be observed in any confirmed Lancian beds,
despite the fact dinosauriferous Lancian beds are known from Saskatchewan to
Texas and sample a wide variety of environments.  There is strong evidence
that some groups of dinosaurs had suffered extinction prior to the K/T
event.

Hope this helps.

                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): 301-314-7843