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Re: dino extinction

Wayne Anderson writes;

>What about Bakker's theory of catastrophic disease? Has this been
>discredited, or is it still in the running? Catastrophic diseases DO
>emerge from time to time -- e.g., bubonic plague and Dutch Elm disease
>-- and can easily be selective about who or what they attack. This may
>very well be why New Zealand has no native mammals, and might also be
>applied to dinos -- no?

The big problem with the catastrophic disease theory is that, while the
disease will weaken the population, it will not be able to kill *every*
animal.  In the study of ecology, there are two main groups of variables
that help determine population dynamics: density independant and density
dependant.  Density independant variables always have the same effect on a
population, regardless of the actual size of the population.  For example,
lifespan (Species X lives for 7 years, this doesn't change as the
population rises and falls).  Density dependant variables are those aspects
who's effect is based on the size of the population.  For example,
predation (a carnivore is going to be more likely to feed on Species X, if
there are a lot more of Species X around).  In ecological terms, disease is
considered to be a density dependant variable.  By definition, even the
most virulent of diseases won't be able to reach every organism in the
species, and it's effect will be lessened as the population drops.  Disease
can weaken a species, but the coup de grace will be delivered by some other

One other problem with the disease theory is that most diseases tend to be
species specific, affecting only a few species, leaving the rest untouched.
Rabies is the only exception I can think of at this time.  Despite how
Bubonic Plague ravaged human populations, I am unaware of any other species
that were affected to the same degree (were the rats that carried the
plague-fleas killed as readily?).  Because of this, I am skeptical of any
major disease wiping out EVERY dinosaur species.

Rob Meyerson
Orphan Vertebrate Paleontologist

"If you're falling from a cliff, you might as well try to fly."