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RE: crocs eating hadrosaurs (was Gr. 9 sci proj)
Nathan, I think my response to Bruce Thompson addresses this (tries
anyway). But I will make some additional comments.
On Thu, 9 Jan 1997, Nathan Myhrvold wrote:
> This comment implies that gigantism was bad, and ultimately unfit. I don't
> see the evidence. Giant dinosaurs dominated the earth for 150 million years
> - twice as long as the period of mammilian domination. Dinosaur did become
> extinct, but not because of gigantism - after all, the small dinos (and many
> small creatures other than dinos) went extinct at the K/T event as well.
Dinosaurs were the best at what they did for as long as you say. My
comments were not meant to imply the reason for dino demise was bigness.
Instead, I argue dino bigness was a response not of creative evolution to
exploit an available niche (because much smaller mammals do that just aswell or
better today). Rather, it was a strategy of defence which, I maintain,
was somewhat pathological with respect to physiological stresses. I also
argue that mammal strategy is superior since, whatever the reason for
dino demise, no big open-field egg layers have evolved to challenge
mammalian (placental at least) dominance. Also, the duration of
dinosaurian dominance says nothing about the respective strategies. The
dominant weapons in most of human history were swords and arrows.
The gun has been around just a fraction of this time. Choose your weapon!
> The larger a mammal gets, the smaller the litter size
> (usually just one for large mammals), the longer the gestation period,
> and the longer the period a mother must care for the young afterwards.
> All of these directly reduce fecundity.
Am I right in saying that an animal bearing one baby which survives has
higher fecundity than another which has 20 but they all die? We cannot
census dino populations, but surely the teeming Serengeti plains are
evidence of healthy mammalian fecundity. I claim that large clutches in
dinos are evidence for high predation rates on eggs 'n offspring, not of
teeming Laurasian plains.
> The hypothesis is that this scale dependent fecundity effectively
> limited gigantism in terrestrial mammals. Dinosaurs appeared to have
> high fecundity, irrespective of their size. Even the biggest dinosaurs
> seem to have had the fecundity of a rabbit (loosely speaking).
Rabbits need lots of babies because lots of them get eaten. This was
probably true for dinos as well. And it still doesn't argue for
> Note that did not MAKE them giants - it just didn't stop them from
> moving in that direction. Presumably other evolutionary pressures
> favored gigantism.
See my post to Bruce. I look forward to your response (but not Ron