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Re: Extinction scenarios




Jeff Hecht wrote:

>  Maybe the real threshold for extinction was
> tolerance to CO or some other toxin from the wildfires?

The problem with this is that this would tend to kill off not just the dinos but
the small mammals, birds, etc.  Atmospheric toxins would not be very selective 
and
would affect the smaller animals as much or more than larger ones. That is why 
the
old miners crough canaries into mines with them.  The birds would die from gas
buildup long before the men would notice it.

Really, I think it makes the most sense to say that with declining populations 
of
dinos (yes I know this is still under debate by some), the Deccan lava flows, 
the
drying of the interior seaways, etc, that there is good evidence that the faunal
ecosystem was undergoing large scale change even before the impact.  The 
asteroid
may simply have delivered a severe enough blow to accelerate the process.  Toby
White made the excellent suggestion that the ability to recover quickly from the
effects of the impact maybe more important in terms of recapturing the niches 
than
the deaths directly caused by the impact. One other final little niggling thing,
the biggest predators after the impact werent mammals from what I understand.  I
seem to recall the diatrymids held that spot for a while, if the Denver Museum 
is
at all accurate.  This would indicate to me that the terrestrial dinos that
survived were outcompeted in the post-impact environment lending credence o 
toby's
suggestion.

Joe Daniel