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





> Date: Sun, 30 Jan 2005 18:27:46 +0100
> From: David Marjanovic <david.marjanovic@gmx.at>
> To: DML <dinosaur@usc.edu>
> Subject: Re: Vegavis gen. nov. - new anseriform in today's Nature

Bois said:
> > A good review of the effect of foxes, cats, rabbits, camels, goats, pigs
> > on
> > 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?

My ref. was a response to your astounding claim that predation has little
effect, little _observed_ effect.  In fact, if
foxes were not possible to control, they probably would have been even more
devastating than they already are.

> > 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.

Behaviors don't fossilize.  Extant birds and crocs have more fixed action
patterns than extant mammals.  Presumably behavioral flexibility is
advantageous, requires more computation, and is derived from vertebrates
with less neuronal sophistication.  Phylogenetic bracketing non avian
dinosaurs between crocs and birds would _infer_ fap's for non-avian
dinosaurs for a first order hypothesis.

> Tell me why mammals didn't outcompete each other...

You're kidding, right?

> 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.

I read a paper on pigeon vertical take off...seems a very specific, highly
derived ability.  But what leaves me nonplused is your outlook on
evolutionary process.  It is a kind of political correctness that argues for
all creatures to have equally valid abilities.  They exist where they are
because they got there first and have not yet been dislodged by a mass
extinction.

> These arguments appear so unreflected to me, so taken out of the 1950s...

Closer to the 1850's, probably.  Closer to Darwin than Gould--allowing for
evolutionary change occuring at many different rates, from many different
causes, with traits having specific value contingent upon specific niches
and specific guilds occupying them at specific times.  Change occurs through
invasion, through adaptive radiation into empty niches, and through
sympatric speciation.

> 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.

Why the focus on azhdarchids?

> 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.

Behavioral flexibilty, smarts, sensory acuity, vertical take-off, aerial
agility, greater protection and nutritional support of fetus, etc., etc.

> 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.

This all seems so _ad hoc_ to me.  Maybe you're on to something.  Do you
feel confident in your reasoning?  How would you know if you were wrong?

> > 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?

Read: Rowe, M. P.  2000.  Inferring the retinal anatomy and visual
capacities of extinct vertebrates.  Palaeontologia Electronica 3:43pp

> > 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".

This would be a very simple-minded ecologist.  In the face of so much
successful invasion into "occupied niches", I wonder how one could take this
claim seriously.

> 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...?

Oh...OK.

> > 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:

I was referring to Phor.  Sorry for confusion.

>...the (bolide) hypothesis is still falsifiable, and thus scientific. You
are
> invited to falsify it. Good luck.

But whenever I bring in a piece of evidence...as in: species x actually
survived but should not have...you respond with: "They were lucky".  How
does one falsify this?  How would you know if you were wrong?