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Re: Upper size limits in dino...

>why is it that large animals often
>seem more prone to extinction?  Comments anyone?

     Well, large creatures show an extreme adaption.  They are a very
specialized adaptation that would tend to suffer more during natural
disasters that directly affected their particular niche.  
     If only a little of their food was gone, or the others of their kind
were seperated from each other (preventing mating with smaller but related
species), or the water (in the case of whales) got too hot to disperse heat
comfortably, or the creature in question's habitat became more crowded, it
would more quickly affect a large creature than a small creature.  The
numbers a niche will support of a community of large creatures is smaller
than the numbers a niche would support of the same species in a smaller size,
therefore there are fewer creatures to survive a catastrophe.
    I think it's just a question of numbers.   If you have a poacher go out
and kill 6 elephants, and those are all the elephants in that valley, there
are no more elephants.  If the same poacher goes out and kills 6 rabbits,
there are still hundreds of rabbits in the valley.  If some elephants
survived, it would take 2 or more years to replace those elephants by
breeding more elephants.  The rabbits would be replaced in one litter.
   I've been curious for a while why gigantism seems to reoccur often enough
in the gene pool, yet extinction seems imminent for such a specialisation.
 Of course dinosaurs had millenia of a relativly uneventful weather pattern;
just continents moving around to bother them, but are they an exception?
 Giant birds came and went,  giant mammals came and went (whales are probably
going), why did dinosaurs survive as long as they did without becoming
extinct sooner?  If the smaller dinosaurs such as Compsygnathus or such were
extinct at the time of the Late Cretaceous, then the dinosaurs were all of a
gigantic type at the time.   Did the presence of a niche of small dinosaurs
lead to the long term survival of dinosaurs as a genus throughout all those
millenia?  On the timeline that was wandering around this mailing list a
while ago, it seems that each small extinction was followed by a smaller
species becoming gigantic to fill an open niche, rather than a gigantic
species proliferating other niches left open by an extinction.  Is this
possible?  Am I misreading something?  Did we get gigantic species spreading
out to other niches, or were these splitting into species and subspecies done
in a period of genetic and geologic calm (such as the ceratopian splitting
into subgroups, or the saurapod splitting into subgroups)
  I'd love to hear more comments.

   Thanks-Betty Cunningham(Flyinggoat@aol.com)