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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.