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Re: Dino size: go on, laugh at me



> On Mon, 26 Jan 1998, Sue Blakey wrote:
> > A second grader in Spain has requested the answer to this question: Why
are 
> > dinosaurs so big?

I should know better than to stick my cervical vertebrae out where I have
no references, but I remember reading one hypothesis for this amazing
phenomenon...

The story goes that the herbivorous dinosaurs -- at least up until the
Cretaceous burgeoning of the angiosperms -- ate food which was high in
fiber, but poor in nutrition.  The largest of these, the sauropods,
flourished mostly before the advent of flowering plants (although, as we
know, a number of Cretaceous sauropod fossils have been found).  The poor
quality of the available foods (conifers, cycads, cycadeoids, ferns, club
mosses, etc.) required considerable processing by the herbivores, who
developed capacious guts (especially the sauropods and the ankylosaurs) for
the purpose of maximizing intake and longer term digestion of the foods. 
Larger herbivores then led to selection for greater size in the theropod
dinosaurs who hunted them, and perhaps there was a mutual escalation of
selection pressures to attaining greater size among carnivores and
herbivores alike.

I don't know how valid this hypothesis is, considering that today's
folivores (leaf eaters), hoatzins and koalas for example, do not attain
gigantic size.  I believe that Robert Bakker's _The Dinosaur Heresies_ may
discuss this topic (though you may need to take some of his arguments with
a grain of sodium chloride).

Ralph Miller III <gbabcock@best.com>

"It's just a possible hypothesis."  (Spoken by Nicholas Geist in response
to objections to his presentation on _Sinosauropteryx_ fibers as subdermal
features supporting a sea snake-like frill at the October 1996 SVP
meeting).