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

Re: Viva Neornithine Birds!



> Of course, not all species are equally susceptible
> to the various effects of
> impacts, and I think this is what we are looking at
> here. Arboreal birds
> will run into trouble when all the trees burn, for
> example. This --
> exaptation for impact conditions -- seems to be what
> you have never taken
> into account so far.

I guess it's a fairly certain thing that the
Avisaurids, if their presently known distribution is
worth anything, didn't stand a chance, for example.
Wrong place, wrong trophic niche, habitat was less
than ideal too. Probably wrong life history: if the
theory that E's had a prolonged growth phase and
therefore more often than N's would occupy subsequent
trophic niches throughout ontogeny is good (which
seems so), this would make them more vulnerable.

The pattern of *extinction* rather than survivorship
might also be looked into. There have been many
dedicated studies for modern taxa (not only birds)
too, FWIW.
 
> > Assuming equal numbers and distribution of
> neornithines and
> > enantiornithines, the probability is .5 ^10 that
> they would _all_ be
> > neornithines.

Equal distribution?? I wouldn't want to assume that.
Ecologially, for most outside factors e.g. Polarornis
was more similar to a sea otter than to a
Maastrichtian galliform in any case, so a simple
geographical analysis is only half the effort.

> >> Well, (the "shorebird" hypothesis) was wrong.

Not... quite... 60-70% of surviving neoavian
*lineages* being some sort of shore-, sea-, or
otherwise "amphibian" bird seems fairly likely. I'd
put the span of reasonability from 50-80%.

> > And it's glib because it inspires glib
> > hypotheses (e.g., the fanciful crab-cracking of
> shore birds).
> 
> Never heard of that one.

Possible but highly unlikely. Marine ecosystems in the
upper oceanic layers (zone of primary production)
should be affected worst in a global comparison
(excluding polar regions), in a broad girdle
stretching throughout the Tropics and again northwards
in the arid areas (which lay further polewards then),
and from there got mixed into the atmosphere. The
subantarctic region landmasses were very likely
retaining most functioning habitat in proportion to
total area, considering that atmospheric dynamics were
unlikely to differ qualitatively from those today.

The air masses of the N and S hemisphere do not mix
quickly; i.e., the S hemisphere Hadley cell got far
less than the 45% of the aerial pollution it would if
the stuff had spread evenly N and S from the Yucatan.

On the contrary, the landmass distribution allowed for
all that gunk to nicely disperse all over the *oceans*
quickly by comparison. Add to that the carcasses of
much of the marine primary producers, and you can
guess what happened: the oceans basically all but
rotted away for some time. This is is barely OK for a
crab, but if you feed on crabs and depend on them
being plentyful, though chance.

The IPCC report reminded me that it should be possible
by now to seriously do some good modelling on this.

It is interesting to think that in some places of S
Australia, the impact effect on (terrestrial)
ecosystems was probably less serious than when humans
entered the scene, and that in these areas,
semiarboreal landbirds might have actually stood the
best chance of survival. There was definitely some
wild weather for many generations anywhere, and some
Very Bad Rain in the first months of the Paleogene,
but quite obviously, entire forests survived
*someplace* judging from the botanical continuity. And
a shrubland, "warbler"ish sort of bird can so much
shrug off a mega-earthquake, and has good odds not to
fall victim to brushfires.

As far as species-level or higher lineages are
concerned, the main dieoff probably took place some
generations into the Paleogene rather than in the
first hours. Survivor populations that weren't
resilient enough went extinct as the remnants of
habitat imploded or changed. For the fossil record, 1
year of 1000 years until a lineage fails is not much
different.

Are there any guesstimates about at what time of the
year the impact happened?

Eike


                
___________________________________________________________ 
Telefonate ohne weitere Kosten vom PC zum PC: http://messenger.yahoo.de