Re: Post-K Aussie Dinosaurs

[Tom Holtz <tholtz@geochange.er.usgs.gov>]

>I've been reading this thread with interest and expectation that it might
>turn to post K dinosaur finds in general.
>
>In *Dinosaurs Past and Present, Vol II*, J. Keith Rigby, Jr. begins....
>
>"Six locations have now producted Paleocene dinosaur remains, primarily
>teeth and more rarely bones, form screen-washed matrix obtained from the
>upper part of the Hell Creek Formation, McCone County, Montana.  These
>fossils are thought to represent primary Paleocene deposition and are not
>derived from Cretaceous bank sources..........."
>
>I am curious about the disposition of Rigby's findings.  Have his
>conclusions received additional attention?  Have they been discredited?
>Ignored?  His extensive field work and lengthy supporting arguments seem, to
>this lay person, to be quite convincing.
>
>Comments?

Well, I won't go into too much of the details (since some of the authors on
the following research are lurking on the net, and can post more fully if
they wish), but here is the general post-1987 take on the "Paleocene"
nonavian dinosaurs:

All of the alledged post-Cretaceous dinosaur material are isolated
fragments (teeth, bone fragments, etc.) found in channel beds.  These could
have easily have been washed out of the sediment banks (of Cretaceous age)
and redeposited in Paleocene rivers.

None (to my knowledge) of the dinosaur fossils from the Paleocene have been
found in lake deposits, nor in aeolian (wind-produced) deposits, nor in
nearshore marine environments.  No articulated bones (which would imply
little-to-no disturbance post-deposition) nor footprints (which would
require a living animal to produce) have been found above (or at the same
level) as indisputable Paleocene markers (pollen, mammals, etc.).

This all strongly suggests that the material currently described from the
Paleocene was all reworked Cretaceous fossils.

However, I don't think even the most extreme catastrophist thinks that
every last individual of nonavian dinosaur was dead by the time all of the
iridium dust fell out of the impact blast.  If the K-T boundary is defined
on the iridium spike, then it is (in my opinion) not unlikely that a few
individuals of some of the late Maastrichtian species survived the blast.
However, there is no evidence yet of breeding populations of nonavian
dinosaurs in the Cenozoic, so the last of their lines may have only made it
a few decades into the Paleocene.

                                
Thomas R. Holtz, Jr.                                   
tholtz@geochange.er.usgs.gov
Vertebrate Paleontologist in Exile                  Phone:      703-648-5280
U.S. Geological Survey                                FAX:      703-648-5420
Branch of Paleontology & Stratigraphy
MS 970 National Center
Reston, VA  22092
U.S.A.