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Re: dinosaur copulation?



>swf@elsegundoca.ncr.com wrote:

>What would the selective advantage be of growing to such large size
>after reproductive age?  Remember, natural selection deals in
>*reproduction* only.  An extreme adaptation can only evolve if it
>improves *reproduction*.  Thus, a non-reproductive gigantic post-
>adult would nt be selected for under most circumstaances.

And yet, somehow, humans have _evolved_ so that their individual lifetimes
_do_ exceed their reproductive lifetime, as least as far as the female half
goes - and, considering the ramp-down in libido, etc, with advancing age,
arguably in males as well.  This kind of stuff _can_ be selected for _if_
the creature is very social - in humans, it obviously was an advantage for
a mother to stop having babies at an age when she was still capable of helping
provide for her children and grandchildren, possibly because she was then
removed from the dangers of childbirth and thereafter able to bridge survival
information to a wider generation band.  The larger size of older dinosaurs
might have made them more formidable in defense of the herd, pride, or what-
ever, and so be selected for despite the early shutdown of the reproductive
system because they can protect the herd (and their progeny) better and longer
if relieved of the brooding instinct.

Another possibility: dinosaurs never grew "up".  Maybe, like fish and
reptiles, they never reached an absolute upper limit in size, but just
continued to grow throughout their lives at a decreasing, but continuing
pace, until they either met a violent end, or until their skeletal structure,
hormone system, nervous system, or whatever was overwhelmed by the demands
of the huge body, which would lead to a fairly quick decline and death.  In
that scenario, "breeding" age might be the middle sizes, and become impossible
later either through the sheer mechanical impossibility or because of declining
hormones versus weight, or both.  In fact, if this is anything close to the
truth, "mature" dinosaurs were much smaller than we presume - a t-rex might be
"adult" and reproducing at 1 ton, and perhaps 20 feet from nose to tail, others
correspondingly smaller. A 30 footer might no longer be able to gestate an egg,
and might no longer have an interest in doing so, but is "coasting" in
evolutionary terms, continued longevity due to a simple side-effect of
metabolic organization.

Larry Smith
larrys@alpha.zk3.dec.com