[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
Re: Vegavis gen. nov. - new anseriform in today's Nature
On Sun, 23 Jan 2005, David Marjanovic wrote:
> "Enough different birds" means one viable population per species, of at
> least 5 species. This can amount to _very_ few individuals. Especially if
> you take the postapocalyptic world into account -- practically no predators,
> no competition.
...and no food.
> _Of course_ the impact theory predicts that dumb luck mattered. It predicts
> continent-scale wildfires -- something may have been in places that didn't
> burn. It predicts humongous tsunamis -- something must have been in places
> where the tsunamis didn't reach. And so on.
But no enantis. What are the odds?
> The best comparison might be: Line up a lot of people along a wall. Then
> give the execution squad imprecise shotguns that strew a large amount of
> small bullets in rather random directions. Give them one shot. Someone is
> going to survive because no pellet happened to hit a vital organ of theirs.
But you can't have it both ways. It's quite laughable, really. And
circular. When you can't lay the extinction to a specific susceptibility,
and since you know the mass extinction was caused by a certain event, the
species that survived must have been just plumb lucky--why? Because the
mass extinction event happened. Again, there is no
non-circumstantial evidence linking _any_ event to any extinction.
> > I think species interactions are common and well-observed phenomena in
> > extant communities. they cause extinction, etc., etc.
> Problems are:
> - They ae much less well observed and studied than you seem to think.
What does this mean? We recently discussed island extinctions caused by
species interactions. Phenomena can always be studies in greater detail.
Current evidence, however suggests that species' interactions are
> - They have never led to _mass_ extinctions in known cases.
Are you sure mass extinctions are that different. Or do they grade into
> > Re: Pterosaurs
> >> Why should they have been? Competition with known birds is impossible,
> >> competition with unknown birds quite improbable, predation is likewise
> >> very
> >> improbable.
> > We have discussed this long and hard before. Don't think you have
> > absorbed/validated any of my points.
> I have understood your points, and none comes close to convincing me.
C'est la vie. Pterosaurs were apparently a hermetically sealed component
of past ecology.
> No, it is not, because your calculation has a serious thinking error. It
> isn't "how probable are 5 out of 5 vs 0 out of 5". It is "how probable are 5
> out of many millions vs 0 out of many millions". There's practically no
> difference there.
Doesn't it reduce to the same thing? Say, a million enantis and a million
neos randomly distributed. Chance of getting a neo is still .5.
> I'm going to tell you something. Another listmember has recently seen a
> lioness on TV that tried to crack an ostrich egg. She just managed to clamp
> her jaws around it, but found herself incapable of biting -- her jaw muscles
> were so overstretched. Eventually she dropped it unharmed. Now please
> explain how a mammal the size of _at most a cat_ is supposed to crack a
> hadrosaur or sauropod or tyrannosaur egg.
Proof that you haven't absorbed any of my ideas! Black-backed
jackals--smaller than lions, and Egyptian vultures--are prime predators of
ostrich eggs. Very small armadillos are the main predators of rhea eggs.
They do it by simply knocking the eggs together!
> I guess this is how ostriches survive in the presence of _high_ predator
Indeed, ostriches nest in regions of _low_ predator density--arid
grasslands...one nest per km^2...very difficult to find...islands of low
> And then come the success stories of dromornithids,
An argument can be made that the predatory regime was milder in Australia.
Certainly, continental immigrants are currently kicking the home team's
That suffered extinction after the immigration of continental predators.
> perhaps gastornithids count, too.
Possibly denizens of swamp lands, traditional refuge from mammalian
predators--became extinct after continental wetlands drained.
> Now, where is the revolution in bird and mammal abilities toward the close
> of the Cretaceous? *Cimolestes magnus* is much smaller than *Repenomamus
> giganticus* which lived some 70 million years earlier.
Size is not all it's cracked up to be! Seriously, I am being conservative
when I claim that end K birds and mammals were advanced relative to their
earlier relatives. Read Pond for advantages enjoyed by placentals, for
> > I recognize the importance of the bolide, the instability of the
> > global habitat. But I think it lacks predictive power, especially
> > now that birds seem to have survived in greater numbers!
> Those numbers are still tiny, as I've tried to explain several times
And I have explained that there is _no_ information on population sizes
from the K/T. For all we know, the surviving populations of "ducks" and
"chickens" were huge!