Re:

["Steve Brusatte" <dinoland@lycos.com>]

On Sun, 02 Jun 2002 15:28:13  
 Sean Carroll wrote:
>I wonder if the original poster here knows about Robert Bakker's theory
>on the K-T extinction (that geographic barriers began to fall, for
>example the Bering Strait, and the intermixing faunas all started to
>catch new diseases they had no immunity too -- much like rinderpest in
>African cattle, brought over from England, or smallpox, brought to the
>New World by the European colonists).
>
>Of course, Bakker doesn't say that this 'explains the rapidity of their
>demise' -- in fact, he says that the evidence is strong that nonavian
>dinosaur populations were in decline (measured by a drop in species
>diversity) for a long time before the boundary. But he does (or did)
>claim that contagious diseases were the primary direct factor behind the
>extinction.

Does anyone take Bakker's hypothesis very seriously?  It fails in several 
categories:

1) As David mentioned, even if dinosaurs did spread diseases between one 
another, this does not explain the extinction of mosasaurs, rudists, ammonites, 
forams, etc.  I once asked Bakker about this in an interview and he didn't have 
anything to counter the argument.

2) The dinosaurs were a large, diverse, and abundant group.  Very few diseases, 
if any, would likely affect every living dinosaur.  Millions of years of 
evolution had made their respective immune systems quite different.  I can't 
think of a disease that, say, can kill every single mammal (which would be 
about equivalent to finding a disease that could kill every dinosaur).  Even 
several diseases being spread between different dinosaur groups is still a 
large stretch.

3) Were more geographic barriers really being broken in the Late Cretaceous 
than during other parts of the Triassic and Jurassic?  Continents have always 
been moving.  Land bridges have always emerged and disappeared.  Populations 
have always migrated.  Why was the Late Cretaceous any different?

4) Even during the most devastating outbreaks, such as the rinderpest outbreak, 
not every member of a population is killed.  Some seem to survive.  Not only do 
some survive, however, but those that survive are stronger.  It's survival of 
the fittest at its best.  A deadly disease offers organisms the chance to 
"develop" beneficial mutations that offer immunity.  This can be seen on any 
farm.  Insecticides are strictly designed to kill insect populations, but 
spraying always creates populations or strains that are more resistant.  The 
same thing should happen during any disease outbreak, unless we dismiss the 
process of evolution!

All-in-all, this hypothesis fails like so many others.

Steve

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