Re: The extinction of small dinosaurs (long again)

[Michael Bruce Habib <mbh3q@virginia.edu>]

> Well, this is an eminently testable hypothesis!  But, let 
> me warn you...full flowering forests are found fairly 
> close to the K/T (Paleocene,I believe).  

Here's the ref if anyone is curious:

Kirk R. Johnson and Beth Ellis 2002.  A Tropical Rainforest 
in Colorado 1.4 Million Years After the Cretaceous-Tertiary 
Boundary Science June 28; 296: 2379-238

> Invasions have caused much extinction today...new birds either evolving
> sympatrically or allopatrically may have developed new strategies that
> were effective against little dinos...And, I find the 
> claim that nothing changes in the biota unless a 
> catstrophy occurs to be unfounded...stuff happens all the 
> time.

I have to disagree slightly here.  The K/T event was a 
global extinction event that killed many higher taxa.  
Invasions are involved in regional extinctions all the 
time, but there is no evidence that they can be a primary 
killer in a global extinction event that kills all 
populations of thousands of species in a short period of 
time.  Also keep in mind that such invasions (of which 
there are many presently) are essentially migration or 
dispersal events.  Speciation and divergence patterns are 
far too slow to constitute a true biological invasion...  

Reason:
Your example above requires that there be no adaptive 
response from terrestrial dinosaurs.  It also requires that 
the same competitive advantage exist everywhere that the 
competing species meet, and that it is significant enough 
among different groups to increase extinction risk across 
entire families. To date, there has been no strong data to 
show that invasions work in this manner.

You do not need a major disturbance to cause extinction, as 
HP Bois points out; invasions and other processes cause 
changes in biotas consistently.  However, to kill major 
groups on a global scale in a short time period _does_ 
require some major shift in conditions.

I would also like to throw in the idea that resistance to a 
bolide disturbance could be much more simple than we're 
making it out to be.  It could be something as simple as 
population size.  Small populations (and relatively large 
species, tertiary predators, etc all have somewhat small 
populations, in general) die more easily.  Kill enough 
organisms and they go first.

--Mike