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Re: Theories on the extinction of dinosaurs



In a message dated 11/22/99 11:42:07 AM Eastern Standard Time, 
nrlongri@midway.uchicago.edu writes:

<<  Of the three, the freshwater aquatic ecosystem is the least impacted; 
crocs, champsosaurs, turtles, various groups of fish, frogs, salamanders, 
etc. all seem to make it through relatively unscathed (again, relatively: 
they probably got only
 99% wiped out or something like that). >>

>From a documentary about cheetahs, I learned that a small breeding population 
did not have enough genetic diversity to be likely survivors.  Is the minimum 
breeding population known for any of these creatures?  Can the dna be tracked 
well enough for any animal(s) to determine whether the number of breeding 
individuals was ever comparatively small?
This might be an argument in favor of a single, widespread extinction event.

Also, NKing@usi.edu (King, Norm R) writes:
<< Perhaps some of the groups that seem to have dropped out in the Western 
Interior were still thriving in the tropics or elsewhere. >>

Dr. Holtz in a previous discussion described an equation which demonstrates 
that an animal need not be extinct to disappear from the fossil record at a 
certain location for a period of time.  Given this, is it ever possible to 
assume from the record that any animal has ever become extinct at a certain 
time?  I'm wondering about the period after as well as before the end of the 
Cretaceous.

As long as I'm asking, I wonder why if primitive birds were so close to 
dinosaurs that the boundary may have been crossed more than once, why 
flightless birds could not have re-evolved the traits which made carnivorous 
dinosaurs so effective, and so become the most successful predators after the 
Cretaceous?  Was the only difference really the proliferation of egg-eating 
mammals?   

Thanks!