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Re: Jurassic Predators vs. Cretaceous Predators


I've no quibble with most of what you wrote, and these predator prey 
ratios are interesting numbers (though they are of course quite 
tentative, and based on assumptions that may well be false.)

But there are a couple of points:

In the middle of your discussion you noted that the Cretaceous
predators were: "the animals that descended from the allosaurs
(i.e. tyrannosaurs), and the ones that evolved (i.e. dromaeosaurs 
et al)."

I think you'll find that a good number of people have their doubts
about such a direct relationship between tyrannosaurids and 
allosaurids.  It may well be that all large Cretaceous predators 
evolved from much smaller Jurrasic ancestors, instead of being 
retreads of the allosaurs.

As to why the environment needed another predator, take a look at
what we have today.  Canids and felines represent two distinct
and diverse groups of predators.  They often overlap in territory
and prey -- even though their design and size may be very different.
Predators aren't "needed" by the environment, predators just 
survive.  If they can get enough food in their bellys, they're not
as likely to notice that the environment wasn't advertising for
new help.  On the other hand, predators die when they don't get
food.  With the exception of exotic predators rapidly expanding 
into a restricted environment, they're not likely to have a
devastating impact on prey populations.  When you grow up in the
same neighborhood with the local bully, you learn how to get away.