Re: K/T birds

[John Bois <jbois@umd5.umd.edu>]

On Wed, 12 Dec 2001, Daniel Bensen wrote:

> I just read the Natural History article about the Gondwanan origin of modern
> birds (VERY interesting, and I'd like to hear the List's opinions about the
> article).

The article makes a good case for pre K/T diversity of neornithes.  I take
issue with the bipolar division proposed for birds at the K/T.  Cracraft
is saying that the bolide hit affected North Hemisphere and that since
neornithes were largely Gondwana species, and since the Southern
hemisphere wasn't hit as hard, they inherited the Earth (rather than
enantiornithes).  My difficulty is that flight enhances dispersal.  This
makes it likely that succesful usurping of Southern niches should be
followed by the same for northern niches.  I know the fossil record
doesn't indicate this yet.  But, if and when it does, it will also
indicate that neornithes were more effective competitors, not the lucky
survivors of a fluke event.
In any case, why, if a considerable diversity of birds survived in the
south, didn't some of their non avian brethren share their good fortune.
I mean, presumably there is a great range of tolerance among the putative
bird survivors; and certainly a similar range existed for non avian
dinosaurs--was there no overlap, or was extinction event so precise so as
to intersect the precise division between the two taxa--that is a surgical
strike, indeed!