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Re: New Cretaceous bird and other papers




On Sun, 17 Feb 2002, David Marjanovic wrote:

> But without a big mass extinction in between, unlike the K-T. Fossils
> regularly show enormous radiations after mass extinctions, molecular clocks
> _never_. Sort of suspect, no?

Maybe I'm misunderstanding your point, but morphological change (as seen
in radiations) should not necessarily be reflected in genes used for
molecular clocks.  Usually (I think) clock genes are relatively
stable--not subjected to selection--and indfependent of morphological
change (e.g., mitochondrial DNA).  Otherwise they would be of little
value.  In this respect how would a mass extinction be recorded in the
genome at all?

> But assuming almost the entire diversity of Neornithes in
> the Cretaceous is IMHO a stretch.

A bigger stretch is imagining how a limited neornithine diversity in LK
could survive while the _total_ diversity of enantiornithes is knocked out
by bolide magic bullets.