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Re: Vegavis gen. nov. - new anseriform in today's Nature
On Fri, 21 Jan 2005, Graydon wrote:
> > Right, but it does show that the ancestors of ducks were present, that
> > the genes in them survived into modern ducks.
> Doesn't show that at all; it shows that the point of common ancestry
> between modern ducks and their next closest non-duck relative is back in
> the K somewhere.
I'm honestly confused and could use some clarification. How are these
positions contradictory? Thanks.
> But you're looking at this as though there was no loss of diversity, and
> we can be sure there was a substantial one, both through finding
> Cretaceous birds that don't have post-K/T descendants, on the one hand,
> and through noting that the extant neornithine bird clades represent a
> small fraction -- and not the most populous fraction in the Cretaceous
> -- of the Cretaceous bird diversity.
There are no data on diversity or population sizes.
> I think you've got 'spared birds' where you should have 'a few bird
> species survived'. There was a massive loss of bird diversity.
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
> People are generally proposing 'dumb luck'; a very few neornithine
> species made it over the boundary, along with maybe *one* Gondwanan
> ratite species. (Or maybe more, but not a dozen.)
Let's for argument's sake say 5 neornithines and 0 enantiornithines made
it across the boundary. What are the chances that this was the result
only of luck: chance of 1 neo and 0 enanti = .5; 2 to 0 = .25...5 to 0 = 1
in 32. Good luck, indeed!
> Every available evidence from the Cretaceous indicates that neornithines
> were not ecologically dominant at that time. Maybe some small portion
> of the then-extant neornithine species were more suited to survive, or
> maybe they just got lucky. It's important to remember that everything
> to do with a mass extinction event does not have a neat casual reason;
> dumb luck *matters*.
Were crocs just lucky? Mammals? Lizards? etc., etc. Or is it just
birds? It seems luck must be invoked when everything else fails. 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.
> Motor-gliders, rather than continuous flappers, ill equipped to cope
> with a month of global storms.
Or, they were already gone.
> > nor enantiornithines; nor would it protect any organism from the
> > proposed conditions e.g., heat radiation from re-entering ejecta.
> Hence the 'dumb luck' part. Sometimes, something would be diving, or in
> a wet marsh, or behind a big tree and then escape the resulting fire.
Curse of the enanti's not to share this luck.
> 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.