C. Rosser,
No, I'm sorry but you are off. We know that there is evidence of
exogenous shocks, most compellingly an asteroid hit, during the extinction
period. What we do not know is what that shock caused. Asteroid hits
don't kill a planet full of dinosaurs. Small dinosaurs survived well, yet
their cold tolerance is even worse than that of large dinosaurs. What
actually happened once the environment changed is a matter for
speculation. It could be that the environmental change merely prevented
the dinosaurs from coming back from an existing threat. We have
relatively little idea what plants were like at that time. There could
have been a dramatic shift in plant biology. New species with poisonous
defences could have sprung up. Trends in forestation could have been
responsible. The dinosaurs could have grazed themselves out of existence.
It's impossible to know.
The important thing is to keep an open mind. The message of
evoutionary biology is that things *always* change.
peace
