[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

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.