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Re: dinosaur->bird when?



>From: pwillis@ozemail.com.au (Paul Willis)
 > 
 > >        I belive that in many ways dinos were already one their way out
 > >millions of years before the boundry and the extinction happened over a very
 > >;ong period of time, you didn't just wake up one morning and find all the
 > >dinos gone.
 >
 > I have seen this claim on other occassions and have to ask; how good is the
 > data on the great dinosaur fade? 


First, even under the best *possible* circumstances, the dating could
get no better than a resolution of a few millenia, at least for large
beasties like dinosaurs.

 > Surely marine invertebrates or the various
 > microfossils would be a much better source of data for population trends in
 > the late Cretaceous and, from what I understand, they show no signs of
 > population fades. So just how good is this dinosaur data?
 > 
Actually, the data is complex, and difficult to interpret.  At the
main boundary layer there is always some apparent staggering of species
disappearances, but this could easily be a statistical artifact.

Secondly, when larger spans of time are covered, there is often some
evidence of *stepped* extinctions, with the steps well seperated in
time.  This pattern *may* also apply to the dinosaurs.  Certainly,
the diverse Early Maastrichtian dinosaur faunas were replaced by
low diversity faunas dominated by just 2-4 species.  (Note, total
*number* of species may not have dropped, but almost all species
were rare except for the few dominants).

swf@elsegundoca.attgis.com              sarima@netcom.com

The peace of God be with you.