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Re: Dinosaurs to birds




On Fri, 22 Jan 1999, Stanley Friesen wrote:

> At 10:54 PM 1/21/99 -0500, John Bois wrote:
> >Then how do you explain the disappearance of enantiornithines?  More bad
> >luck? 

> That is certainly possible.  The exact factors that differentiate survival
> and non-survival in a mass extinction are not known, and are probably
> complex.  

Indeed it is not even known if there _was_ a mass extinction event in the 
lives of birds.  As I have tried to argue, the speciation and extinction
of enantiornithines and neornithines seems to have taken place at a time
remote from any "event".
What then?

> It is very likely that many traits that are adaptive in ordinary
> times have little significance during mass extinctions, and it is possible
> that accidental traits, that are selectively neutral most of the time,
> become critical to survival.  I would call that luck.

OK.  But this is absolutely hypothetical, right?  Whereas I can use the
fossil record to show trends in extinction and possible adaptations that
influenced those trends, can you show any evidence to support your
hypothesis of luck?  And if not, why should luck be the default
hypothesis?

> In addition, many sorts of stress have an unpredictable aspect to them.
> Even in areas otherwise stripped of life by the Mt. St. Helen's explosion,
> there were small, protected sites where a few plants (and presumably
> animals) survived.  Presence in such spots is certainly largely a matter of
> accident.

OK to Mt. St. Helens.  And OK to the idea.  But there is no evidence of
any kind connecting any event to any extinctions at the K/T!  Again, why
is luck being advanced as a default hypothesis in the face of
evidence of cross-K/T radiations of species (mammals and birds), rigid
patterns of extinctions, and the apparently consistent pre-K/T decline  
of non-avian dinosaurs?