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



----- Original Message -----
From: "John Bois" <jbois@umd5.umd.edu>
Sent: Wednesday, January 26, 2005 6:57 PM

>> "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.


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.

Makes a good story, anyway.

Good or bad, it's a direct logical consequence of an impact of that size.

> But no enantis.

There could well have been some that survived all this.
They would then have entered the above scenario.

When does a good narrative become good science?

When it becomes testable.

...I'm sure you agree that some causes can only
lead to small extinctions while others can only lead to large extinctions.

Predation/competition could theoretically lead to small and large extinctions. Physical calamities ditto. So, no...I don't accept your premise.

Why shouldn't there be an upper limit to the effects of predation and competition? It's really hard to imagine a predator or group of predator species that could have an effect the size of the K-T mass extinction -- globally.


If pterosaurs did decline (if!) as a
result of species interactions, I would hypothesize that the predatory
environment got more intense over the K as a result of adaptations of
mammals and birds.  Some species were more able to withstand this
environment, ptereosaurs weren't.

Sorry for forgetting predation -- but what are those adaptations of mammals and birds, and why should azhdarchids first survive for some 60 million years and then die out at the same time as everything else does and a huge planetoid crashes down?


In this view, large body size has
little to do with it--except that, large bodied pterosaurs were more
likely to be able to nest in more remote locations..and that this
afforded them some protection.

Then why do you think something evolved precisely at the boundary that was able to plunder those remote locations as well?


...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)?

Has it gotten my point across? :-)

ostriches and rheas survive just fine...

Even after suffering greater than 90% nest/chick predation to the first year.

Yes, even then. They are r-strategists. Like, for example, sauropods.

> 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*).

What is your explanation for this astounding diversity of non-ratite big birds on these southern continents?

That those of the northern continents ( = Gastornithidae and seemingly Phorusrhacoidea) died out around the Eocene-Oligocene mass extinction. Respectively that dromornithids never got out of Australia. :-|


capable of global travel. Why not on Northern continents?

The first half of the first sentence is missing, so I don't understand that.

Perhaps _Titanis_ enjoyed immunity in the swamps.
Hey, perhaps gators inadvertently protected their
nests as they do other species today.

*Titanis*? In swamps? This was a grassland runner, with leg proportions like an ostrich. Plus, it was a top predator, certainly capable of defending its nest at least as efficiently as an ostrich (...known to kill lions with kicks).


Were gastornithids not thought to be wetland species?

Absolutely everything was thought to be a wetland species 50 years ago. And every sediment except the most obvious desert was thought to represent a wetland, even the Morrison Fm.


The story I read only about ten years ago was that these
species became extinct in NA and Europe at different times,
but both coincident with drying periods on their respective continents.

Up to the, say, 70s, people believed in continent-scale drying periods... do you happen to have a ref?


> 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 think we are coming together on this! Exactly. We _don't_ know.

We don't _need_ to know, and this is an important point. We know that _enough_ survived. Therefore all hypotheses that allow the survival of this minimum number, while allowing the survival of less than that minimum number of other clades, are a priori acceptable. The impact hypothesis fits between these brackets.


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.

Oh, no...we _do_ know.

We certainly know, within error margins, things like the kinetic energy of the impactor. We also have some good clues on what that amount of energy can do.