re: Paleocene dinos

[Norm MacLeod <nm@xxxxxxxxx>]

In response to C.N. Trueman's query:

There are several tests which can be applied that use positive 
evidence to test the reworking hypothesis.  I'm revising a paper on 
this topic right now.  It would take too long to go over all the 
methods but I think you are on a very robust research track by 
looking at geochemical indicators.  In the Paleobiology paper Gerta 
and I review and slightly extend Barerra and Keller's (1990) method 
of comparing the stable isotopic signal for occurrences across the 
boundary interval.  If Danian occurrences of "Cretaceous" species 
are reworked they should have Cretaceous isotopic signals.  
Barrera and Keller (1990) showed that Herterohelix globulosa 
occurrences in the lower Danian had very different signals when 
compared with Upper Maastrichtian occurrences of the same 
species in the same section.  These data have convinced many that 
this species survived (it was previously considered to be restricted 
to the Cretaceous).  Keller and her colleagues have been working on 
this problem for several years now.  They have a lot of data and, as 
you might expect, a lot more survivors from several different 
boundary sections/cores.  Some of the data is out and some is still in 
press.  We've been considering writing a review paper later this 
year to bring all of the isotopic evidence together.  This technique 
should work on bone.  You have to be careful about  diagenesis and 
possible metabolic effects (see the Paleobiology paper) but 
I think geochemistry represents an excellent line of positive 
evidence.  There are other tests for reworking but none that are as 
definitive as the geochemical / isotopic approach.  I'd be very 
interested to learn what you are investigating along these lines.


Norm MacLeod