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Re: Theories on the extinction of dinosaurs



I've gotten to some more of the messages I've been archiving for the last
couple of weeks, but this subject still seems to be active.  The discussion
sure seems to highlight to difficulty in making interpretations of
uncontrolled data (i.e., non-experimental).  

I wonder if we really have a good enough record of the fortunes of dinosaurs
in the latest Cretaceous to know whether the whole clan was in decline.  As
Dinogeorge said, some groups were doing fine.  The fossil record from the
Western Interior of the US and Canada suggests both.  But what about in
Africa, Europe, and South America at the same time?  The distribution and
extent of environments were changing in the Western Interior at that time
(but then, they always were, everywhere), so there may have been more
selection with time for groups that lived in the settings that are
preferrentially preserved, and, preservation may be better (maybe more
likely) in some environments.  Perhaps some of the groups that seem to have
dropped out in the Western Interior were still thriving in the tropics or
elsewhere.

What about the Early Cretaceous record, or that of the early Late
Cretaceous.  The quality of those records is less than that of the latest
Cretaceous.  Perhaps the fortunes of dinosaurs were waxing and waning all
the time everywhere, and so there is no special significance to a perceived
decline near the end of the Cretaceous in the Western Interior.  However, if
we don't have as good a fossil record from the Dakota (Early to Late
Cretaceous, depending on location) or Chinle (Late Triassic of the Colorado
Plateau), for example (and elsewhere in the world at the same time; and how
"same" is "same," just the same stage--Mesozoic stages lasted for millions
of years) we can't make good enough comparisons to know if our perceptions
reflect history accurately.

Previous comments here show we don't really have a good grasp of how intense
the impact effects were.  Perhaps they were intense enough that it would
have been irrelevant whether dinosaurs were in decline (again, as some have
suggested here, but others think it was just the straw that broke the
camel's back).

Perhaps a very diverse fauna, such as those in moist tropics today would
have been more vulnerable to any environmental perturbation, because of
narrower adaptive range.  Great diversity may mean more specialization,
while less diversity may mean more versatility--the survivors were the best
at adapting to rigorous conditions.  So, how do we know that we shouldn't be
thinking that because dinosaurs were becoming less diverse (seemingly!),
they should have been able to survive such a perturbation relatively well?

I'm always concerned about over-interpretation of data.  But what should we
do with all the data we have--just let it sit there without interpretation?

I'm rambling again.