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Re: Vegavis gen. nov. - new anseriform in today's Nature




On Sun, 30 Jan 2005, Graydon wrote:

> Ostriches are not more of an R-strategist than a hadrosaur -- ostriches
> definitely do care of the young, where that's only inferred for one
> hadrosaur...

And no sauropods.

> There's every possibility of variation in nest care among
> them.

Yes.

> As a general rule, clutch size ties tightly to mortality and resources;
> those big hadrosaur clutches indicate some mix of lots of mortality and
> plentiful food, or at least a mortality curve that stays under the food
> supply as a reliable matter.

Right.  There is nothing magical or superior about large clutch size or r
strategy _per se_.  But they do indicated high mortality--and high
predator pressure!  This is the conclusion also of TE Martin's study of
North vs. South hemisphere birds (greater clutch sizes in comparable n vs. s
clades reflects greater pred. pressure in Nth--from continental
predators).  The idea that often gets a free pass is that an endless
supply of babies as food somehow satisfies the predators allowing the
parents to keep a couple for their genetic endowment.  In the case of
ostriches, they exist thanks to the fact that are very
effective at hiding--because they are practically immune to all
population deepression as adults.  But this doesn't mean they will keep on
keeping on until the next rock falls from the sky!

Which leads me to ask if it is true that sauropod diversity declined?  And
why do we think they declined?