Re: K-T Theories

[larrys@zk3.dec.com]

>I went to Dr. Bakker's lecture last Friday here in Portland, Or.  He promotes
>the disease theory of the K-T boundary.  I still don't find it reasonable, and
>would like to hear from someone who either promotes the theory or at least
>understands it.

I don't know that I _agree_ with it, but having just finished Dr.
Horner's book, I think I _understand_ it.  Let me take a crack at
it, and then we'll let the experts touch it up.

As I understand his logic, the major dinosaur groups evolved more
or less in isolation on the various continents over a long period
of time.  When the continents came together, or were otherwise
linked, the different populations had opportunity to mix for the
first time in many millions of years.  Each population had a pool
of diseases that developed with them in isolation, and to which
that group had a high degree of immunity, but that immunity was
very specific.  Mixing allowed disease organisms access to new
population that had evolved _no_ immunity to _them_, since their
immunity was specific to _their_ own diseases.  And, of course,
vice versa.  So every dinosaur population was exposed to pathogens
which they had not evolved with or met before, and to which they
had no immunity.  Not _one_ disease - hundreds, maybe thousands.
What happened to the dinosaurs, by this theory, was a magnified
version of what the white men did to the indians in the US - many
more died from smallpox, plague, whatever, from Europe, than ever
did from bullets.

Horner bases this idea on the fact that the KT boundary is a time
when continents were linking up again, either by land bridge as
the sea levels changed, or by outright collision.  I gather there
is some correlation between such linkups and previous, less spec-
tacular die-offs.

Myself, I think he makes a good case, but there _was_, undeniably,
a major impact in the Yucatan.  My guess is the dinosaurs, after
a hundred million years of ascendency, ran into a string of bad
luck, meeting up with an asteriod at a time when disease and per-
haps other factors had pushed them into decline, as with previous
extinctions.  But this time, there were no dinosaurs left to pick
up the pieces.

Thanks for talking about dinosaurs.

regards,
Larry