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Jurassic predators vs. Cretaceous Predators (we've got a



        Hello!
        I guess it has been a while since I last wrote (the last time lead
to a discussion about dinosaurs and the (in)convienience of having hair on
their chests :-)).  However, I'm back now, and had a question that
eventually brought up some more questions.
        Anyway, I was lying down one day, flipping through a copy of
Bakker's _The Dinosaur Heresies_.  I noticed that he said in one chapter
that the predator/prey ratios for Jurassic animals were very low (I believe
that 1%-5% predators in a population was the the statistic).  Cretaceous
animals were slightly higher.  Then, I noticed something else about jurassic
carnivores.  Bakker argued that they were warm-blooded, of course, and would
therefore have to consume mass amounts of food to keep warm.  A ceratosaur
would take five years to grow up, and the amount of food to supply its needs
throughout its life would be equivilent to 30 tons of meat.
        So I did a little thinking, and set up an entirely fake jurassic
environment for testing.  Assume that on some little, insignificant island,
there are only 1,000 dinosaurs, each of the herbivores weighs 1 ton.
According to the ratios of carnivores and herbivores, 10-50 of those 1,000
dinosaurs would be predators.  Assuming they are warm-blooded, and none of
the dinosaurs reproduce, this means that during the lifetimes of the
predators, they consume 300-1,500 animals weighing one ton each.
        To me, that seemed amazing.  There were practically no predators at
all.  Only a mere 1/100 or 1/20 (max) of the population was composed of
carnivores.  But the tiny population could still control populations better
that most animals today.
        However, in the cretaceous, things get a bit more complicated.  You
have a few major groups of predators.  You have the animals that descended
from the allosaurs(i.e. tyrannosaurs), and the ones that evolved (i.e.
dromaeosaurs et al).  So the large carnivores would have to be warm-blooded
if their ancestors were, and they would probably do a great job of
controlling populations assuming that they followed in the footsteps of
their relatives.  However, you also have the 'new' groups of dinosaurs.
They were built to kill, and probably good at it.  But did the environment
really need another predator?  Was there enough food to go around?  Did this
'ecological mishap' really occur, and if so, did it make the dromaeosaurs
defunct before the end of the cretaceous?  Oh, dear!  It goes on forever! --
>From _Through the Looking Glass_, Lewis Carroll

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Nick Reiman                       
Paleontology Collections Assistant-- **  Future (next year) student at
Mullen High School
Denver Museum of Natural History    **  WWW--The Unofficial Dinosaur Homepage--
E-mail--shasta@rmii.com                       **  http://www.rmii.com/~shasta
--------------
   "My God," Ellie said softly.  They were all staring at the animal above
the trees.  "My God."
   Her first thought was that the dinosaur was extraordinarily beautiful.
Books portrayed them
as oversize, dumpy creatures, but this long-necked animal had a
gracefulness, almost a dignity,
about its movements.  And it was quick--there was nothing lumbering or dull
in its behavior.
The sauropod peered alertly as them, and made a low trumpeting sound.  A
moment later, a 
second head rose above the foliage, and them a third, and a forth.
   "My God," Ellie said again.
                        --From Michael Crichton's _Jurassic Park_
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