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Re: cause of Gigantism in sauropods
On Feb 7, 2011, at 10:05 AM, "email@example.com" <firstname.lastname@example.org>
>>> Another is that many sauropods "overshot": they are far larger than
>>> required to be effectively immune to predation.
> Are they? Even adult African elephants, which are *at least* 20x the mass of
> lions, are occasionally killed by lions. Lone wolves can kill moose 10-15x
> heavier. Was any sauropod actually 20x or more heavier than the largest
> contemporaneous predator?
This why I used the term "effectively". Elephants are killed by very large
groups of desperate lions on very rare occasions. The effective rate of adult
mortality to predation among elephants is so small that the selective
coefficient for larger size to escape predation in those animals must
necessarily be tiny. I am not aware of confirmed accounts of lone wolves
killing healthy adult moose; any references there would be great (sounds
intense!). I suspect it is a very rare event, as well.
I get the impression that something in our general mode of thinking or culture
has made the idea of vertebrate predators regularly killing prey many times
larger than themselves seem intuitively reasonable, even though the data
indicate strongly otherwise. Rates of such events are a bit higher for flying
predators, but otherwise, cases of predators killing relatively giant prey
appear to be exceptionally rare. The only "common" cases I know of are at the
smaller end of the mammalian body size spectrum (weasels killing rabbits, for