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Re: Vegavis gen. nov. - new anseriform in today's Nature
On Sat, 22 Jan 2005, David Marjanovic wrote:
> The difference is small. *Vegavis* must have acquired some mutations since
> it split from its last common ancestor with ducks; those genes are gone.
Oh, right. Of course.
> > But this is _not_ known. As has often been pointed out on this list, bird
> > fossils are so rare as to provided only a sliver of insight into K/T
> > ecology.
> Then why do you make a strawman and say "spared birds"?
Don't understand the question. Birds weren't supposed to be spared,
except for a freak, lucky, single flock, as I remember Feduccia's
crab-cracking shore birds. But it seems to be more complex than this now.
If enough _different_ birds made it across, they were, in a sense, spared.
> > Let's for argument's sake say 5 neornithines
> > and 0 enantiornithines made it across the boundary.
> Five what? Individuals? Populations? Species? (Five species are the minimum
> currently required by the fossil record; this could mean 5 populations, but
> never just 5 individuals.)
Five whatever neornithines vs. zero whatever enatiornithines
> Certainly to some extent. Why did "pediomyids" die out but other shrew-like
> mammals survive?
I know luck plays a role. But I'm not sure why one would invoke it in any
specific instance--I mean, one would have to rule out other causation--and
we know so little.
> > It seems luck must be invoked when everything else fails.
> The impact theory _predicts_ that dumb luck mattered.
I think not, unless you mean dinosaurs were unlucky to require big amounts
of food. Otherwise there is a kind of surgical strike quality about it.
> > Sure, luck could have spared some birds--but this is just another
> > hypothesis for now. I think we ought to be careful how far we go
> > to prop up causal hypotheses. Skepticism, and all.
> That's all fine. Assumptions of dumb luck are indeed very hard to test. You
> are invited to come up with a better idea.
I think species interactions are common and well-observed phenomena in
extant communities. they cause extinction, etc., etc. I think they
played a large role in these extinctions...hard to test also.
> Why should they have been? Competition with known birds is impossible,
> competition with unknown birds quite improbable, predation is likewise very
We have discussed this long and hard before. Don't think you have
absorbed/validated any of my points.
> > Curse of the enanti's not to share this luck.
> Perhaps you are exactly right.
Again, it is highly unlikely that several members (pops) of one clade made
it through and none of another did.
> >> Note that *nothing* terrestrial with an adult body mass over 10 kg made
> >> it. That says a great deal about food availability.
> > Sorry. It doesn't "say" anything. It is a piece of evidence; can be
> > _interpreted_ many ways.
> How do you interpret it?
In the presence of extant mammals and birds, large egg layers are unable
to make a serious go of it. Large egg layers have not _surrendered_ these
niches, they are unable to enter them. There are exceptions to this--but
they tend to be in places of low predator (mammal and bird) density. I
think the revolution in bird and mammal abilities toward the close of the
Cretaceous had something to do with it...and that they continue to have an
influence in reducing the viability of > 10 kg. egg layers. 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!