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Re: Vegavis gen. nov. - new anseriform in today's Nature
A good review of the effect of foxes, cats, rabbits, camels, goats, pigs
Australian native faunal diversity can be found in:
What do you suggest to introduce _to the entire world_ at the end of the K
to kill off some 3/4 of species?
It's a bleak picture...and without management would
lead to close to a mass extinction.
- It's by no means global.
- Even if it were global at the same death rate, it would _at most_ be
comparable to the Eocene-Oligocene transition (which took much longer and
consists of more than one event).
Sorry for forgetting predation -- but what are those adaptations of
mammals and birds...
Behavioral flexibilty, smarts, sensory acuity, vertical take-off, aerial
agility, greater protection and nutritional support of fetus, etc., etc.
Aha. Interesting. Then tell me what the behavioral flexibility of any
non-neornithean dinosaur were, for starters. Tell me why mammals didn't
outcompete each other, not to mention everything else, considering how
different their methods of protection and nutrition of the fetuses are.
(BTW, this is a point where it's easy to make an argument that marsupials
have an advantage over placentals.) Tell me why you think enantiornithines
and pterosaurs were incapable of fast and/or vertical take-off. Tell me why
you think they were less agile. Tell me. Bring it on.
These arguments appear so unreflected to me, so taken out of the 1950s...
...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
planetoid crashes down?
That's an easy one...it was predation/competition
from rapidly evolving neornithines.
Either that or it was the planetoid.
Neornithines? The famous "heavy-bodied ground bird", which is basically what
*Vegavis* is, predating on or competing with azhdarchids at _any_ stage of
the latters' life cycles??? That's hard to imagine. You'll need something
more similar to *Harpagornis* to get that point across.
> 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
able to plunder those remote locations as well?
Borrowing your logic style for a second: because that's when they
Well... there's a way out of this logical circle. We already know that the
Chicxulub impact coincided with the mass extinction, Keller notwithstanding.
We don't know if the evolution of any "key apomorphy" coincided with it.
Sorry I left this bit out. No. What you are saying is that there is a
higher susceptibility to extinction in Enantiornithines.
Indeed I say that at least some enantiornithines were more susceptible to
the effects of the impact than at least some neornithines. Again, here's
why: The avisaurids and especially *Enantiornis* were rather large. There's
some evidence that both belong to a clade of predatory birds -- if so, they
were likely terrestrial, and more or less top predators, which means they
were in the end dependent on green plant parts, and having smaller
populations to begin with. "Heavy-bodied ground birds" able to live off
seeds and insects should be expected to fare better. No known
enantiornithine seems to have had such an ecological niche. *Lectavis*, if
indeed a wader, and *Yungavolucris*, if indeed a diving bird, could have
been parts of freshwater ecosystems, thus much less directly dependent on
green plant parts and thus more likely to survive; but don't ask me if I
interpret too much into these leg fragments.
>>> > 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
>> species found in Riversleigh (relevant for the famous *Bullockornis*).
Things you probably already know:
Population density in one area does not indicate continental density.
I'm not even talking about population densities. I'm just mentioning the
presence of big, powerful predators.
Australia's soil and increasingly arid climate was not condusive to
continent-wide high predator density.
Fine -- rainforests usually or always grow on horrible soil, and Australia
was not yet arid in Riversleigh times.
Now, either the marsupials were not competent in this respect,
or the dromornithids were superior defenders.
Look at the beak of *Bullockornis* and tell me about the latter possibility.
Dromornithids, if they were like most birds, could not see at night.
It is _quite_ hard to believe that birds should be so night-blind unless
specially adapted (owls...). Could you explain this in more detail?
But, if dromornithids are geese they had a global distribution! The
question is: why didn't geese evolve this morphology in other
parts...specifically, in Northern continental parts.
The first answer you'll hear from an ecologist will be "because the
ecological niches of dromornithids were already occupied by other animals
outside of Australia". It would be quite helpful if we could agree on what
those niches were, though... there aren't any nitrogen isotope analyses of
dromornithid bones, are there...?
See above comments on nest defense. I'm trying to argue a general
principal. You are refuting it with an exception...a short-lived relict
a once grand adaptive radiation.
Excuse me... ostriches never had a "grand adaptive radiation". AFAIK there
were never more than 2 or 3 species at the same time all over the Old
World. -- Phorusrhacids are another story. They did have a radiation:
This shouldn't take our focus away fromthe
central question: what caused this radiation to implode.
For phorusrhacids, I suspect South America's local mass extinction 3.3 Ma
ago, plus humans killing off the prey of the survivors. Sure, the evidence
is thin for the latter part... but the Pleistocene *Titanis* and the unnamed
one from Uruguay don't go away.
> 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?
I think it was this: Andors, A.V. 1988 Reappraisal of the Eocene
Diatryma [Aves: Anserimorphae]. Pages 109-125in K. E. Campbell, Jr., ed.
Papers in avian paleontology. Honoring Pierce Brodkorb No. 36 Science
Series Natural History Museum of Los Angeles County.
Ah, thanks. I remember various harsh criticiques of that paper, though I
don't know if anything about habitats was among them...
We don't _need_ to know, (exact population survival data) 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.
This is indeed the ideal hypothesis! A Teflon hypothesis.
Again: Anything that fits between the constraints is fine. If you find more
narrow constraints, please tell me, and we'll see if the impact hypothesis
still fits between those.
Competition and predation, however, seemingly fail at allowing only
the survival of less than the minimum of _most_ clades.
We certainly know, within error margins, things like the kinetic energy
the impactor. We also have some good clues on what that amount of energy
OK...but relating all of this to specific survivorship is a weakness.
So what? I can turn this on its head -- in fact, I _should_: it's a sign
that the hypothesis is still falsifiable, and thus scientific. You are
invited to falsify it. Good luck.