Re:

["David Marjanovic" <david.marjanovic@gmx.at>]

> On Tue, 18 Dec 2001, John Bois wrote:
> > The article makes a good case for pre K/T diversity of neornithes.

Though Cracraft's phylogenies may overestimate it, e. g. he gets moas +
kiwis rather than rheas as basalmost ratites, and then says the former must
have walked to New Zealand as long as that was possible because it is most
parsimonious to assume that the last common ancestor of all ratites was
already flightless. The latter is a case where IMHO parsimony can't be
usefully applied -- why should it be so improbable that only by coincidence
all living ratites are flightless. Furthermore, he gets rheas and ostriches
as sister groups, and he thinks ostriches are fundamentally African, so he
still thinks they must have diverged in the Early Cretaceous when SA and
Africa separated. AFAIK ostriches first appear in Eurasia, so they may IMHO
have drifted there on India straight from Antarctica. Let's find some
fossils :-)

> > 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
> > 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.

You assume "successful usurping", Cracraft and AFAIK the rest of the world
don't...

> > In any case, why, if a considerable
> > diversity of birds survived in the south,

In Antarctica, not just the southern hemisphere.

> > 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!

Let's consider the easily predictable effects of darkness alone: All green
plant parts die off, therefore the herbivorous dinos die off, therefore the
hypercarnivorous dinos die off. Dromaeosaurids can probably be regarded as
the latter. Seed-eating birds probably won't die off because of darkness
alone, neither will insect-eaters, as long as the insects don't depend on
green plant parts, but they will certainly suffer great losses that won't
let them unscathed either.

> Things aren't quite that simple. Even rather narrow water gaps are
> actually rather strong barriers to bird dispersal, especially for
> landbirds. The avifauna on either side of Wallace's line or the
> Mocambique channel are very different. Note for example that no
> woodpecker has yet made it to either Australia or Madagascar despite
> ample empty niche space.

Not exactly empty. In Madagascar there's the famous aye-aye, in New Guinea
at least there is a very similar possum. In Messel there were convergent
anagalid mammals, and in Liaoning there was the still undescribed near-bird.

> Also in the Maastrichtian the continents were actually unusually
> isolated. New Zealand/New Caledonia, Madagascar and India seem to have
> been completely isolated. South America/West Antarctica/East
> Antarctica/Australia were probably only connected by isthmian links
> which would have acted as filters

in combination with ecology: Why are there no tree sloths in the USA?
Because there are no tropical rainforests there, or (counting Florida) at
least between there and southern Mexico.

> Actually there are some evidence for Late Cretaceous neornithines in the
> north. In addition to the "transitional charadriiforms" both
> presbyornithids and lithornithids have been reported, though not well
> published as yet. If the identifications are correct this implies that
> palaeognaths and galloanseres had a cosmopolitan distribution in the
> Maastrichtian.

(The validity of Galloanserae is disputed in the Ostrom Symposium volume on
both morphological and molecular reasons. Haven't read it.)

> As for the survival of birds at the K/T,  the fossil record is
> compatible with a scenario where _no_ birds, either enantiornithine or
> neornithine survived in the north and where only a few (perhaps no more
> than 10-15 species) of neornithines survived at middle to high latitudes
> in the south.

I agree.

> Note that there was definitely enanthiornithines in the
> south as well. They are well attested for South America and the
> Maastrichtian birds from Madagascar (Vorona and Rahonavis) are anything
> but neornithine.

In Antarctica, however, only neornithines have so far been discovered.

> As for why only neornithines survived there is evidence that
> enantiornithines were at least partly poikilothermic

Aw! You don't believe that, do you? There is a much, much better
explanations for their growth rings: they slowed down the basic theropod
style of growth to stay small, convergently with *Rahonavis*
(*Confuciusornis* had the "basic style" and probably just stopped growing
earlier than *Tyrannosaurus*). Refs are the 3 Nature articles on dinosaur
growth which I can't find at the moment.