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Re: Vegavis gen. nov. - new anseriform in today's Nature
----- Original Message -----
From: "John Bois" <firstname.lastname@example.org>
Sent: Tuesday, January 25, 2005 12:54 AM
"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
...and no food.
This is only a factor at the start of that epoch -- and it is precisely
where the ability to subsist on seeds and/or insects comes into play.
_Of course_ the impact theory predicts that dumb luck mattered. It
continent-scale wildfires -- something may have been in places that
burn. It predicts humongous tsunamis -- something must have been in
where the tsunamis didn't reach. And so on.
But no enantis.
There could well have been some that survived all this. They would then have
entered the above scenario.
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
But you can't have it both ways.
I must have it in more than just two ways because the impact of such a huge
rock has more than two effects. Some of those kill everything with a more or
less equal probability, some don't. See above.
> I think species interactions are common and well-observed phenomena in
> extant communities. they cause extinction, etc., etc.
- They ae much less well observed and studied than you seem to think.
What does this mean?
Firstly, the big cases of what were once presumed to be cases of
competition-caused extinction are not all that well studied. The Great
American Interchange is an example. Secondly, competition on a small scale
has not been observed _so_ often either.
- They have never led to _mass_ extinctions in known cases.
Are you sure mass extinctions are that different. Or do they grade into
The question is wrong here. I'm sure you agree that some causes can only
lead to small extinctions while others can only lead to large extinctions.
Whether there are middle extinctions or not is irrelevant here. I think that
competition can (on a global scale) only lead to rather small extinctions;
C'est la vie. Pterosaurs were apparently a hermetically sealed component
of past ecology.
I'm just talking about the azhdarchids: *Quetzalcoatlus*, *Hatzegopteryx*,
*Arambourgiania* and the unnamed Spanish monster. No known bird was able to
compete with them. Sure, we may see "the ghost of competition past" here;
birds may have been the reason for why these pterosaurs got so huge; but
this is a different question.
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
out of many millions vs 0 out of many millions". There's practically no
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.
Hm... I'll try to visualize:
Imagine a box with half a million black and half a million white
balls in it. You take 5 balls out; if you draw a black ball, it symbolizes a
bird species that goes extinct, while a white ball is a surviving species.
How probable is it that all 5 are black and that all 5 are white?
I'm too lazy to do the actual math now, but in any case both probabilities
And now the interesting things start. What if, because of their
different ecological niches or whatnot, the ratio of black to white balls in
the box is indeed 1 : 1 for Neornithes, but 1 : 4 for Enantiornithes? Just
pulling numbers out of thin air (obviously), but I think it gets my point
across. And what if the total number of balls per box is unequal (which is
of course highly likely)?
They do it by simply knocking the eggs together!
OK. Anyway, I shouldn't have started this in the first place; ostriches and
rheas survive just fine...
I guess this is how ostriches survive in the presence
of _high_ predator diversity.
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.
Explain this to *Thylacoleo carnifex* (relevant for the last known
dromornithid, *Genyornis*)... and to the many large dasyurid and thylacinid
species found in Riversleigh (relevant for the famous *Bullockornis*).
That suffered extinction after the immigration of continental predators.
Explain this to *Titanis*, an immigrant to North America and the largest
known phorusracid, and to its unnamed contemporary in Uruguay. Both lived
some 3 million years _after_ the Great American Interchange.
And had survived the local mass extinction of South America that
happened shortly _before_ the Interchange, at the same time as an impact off
perhaps gastornithids count, too.
Possibly denizens of swamp lands, traditional refuge from mammalian
predators--became extinct after continental wetlands drained.
Ah, the continent-sized wetlands that people used to imagine fifty years
ago. One could become nostalgic. -- The distribution of gastornithids across
all three northern continents seems to be at odds with such a restricted
ecology. Besides, don't they co-occur with several "creodonts" each?
Read Pond for advantages enjoyed by placentals, for example.
Could you give me a more specific citiation? (And should I list some
advantages of marsupials over placentals?)
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!
What about "for all we know, they were tiny"? I _really_ think we can
_exclude_ the possibility that they were "huge", because, after all, the
impact of a 10-km rock _is_ The End Of The World As We Know It. Sometimes I
think you're trying to non-discuss the entire impact away.