Re: "But What About The..." arguments (longer again...)

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

OK -- back to dinos:

----- Original Message -----
From: "John Bois" <jbois@umd5.umd.edu>
Sent: Thursday, June 06, 2002 5:25 AM

> > > Things the bolide "null" hypothesis has yet to refute: Neornithine
birds
> > > outcompeted enantiornithine birds;
> >
> > First I'd like to have some evidence that they did, and a hypothesis
about
> > how they possibly did it.
>
> Evidence is enantis disappear and neos diversify.  Note: this is the same
> evidence for your preferred hypothesis.

Yes. Question is when that happens, and I'm not sure the fossil record is
good enough at the moment to test who's wrong here.

> But mine is more parsimonious
> since, a) competition/predation are observable phenomena and are in
> operation today;

That doesn't mean anything. That we can't observe a teraton impact, a flood
basalt eruption or a running animal that weighs 5 tonnes doesn't mean that
never happened, too bad for Lyell. The present is not the key to the past.
The past is the key to the present, and to the future.
        Wait. Competition is _hardly_ observable. The ghost of past
competition, as niche partitioning is called, is very easily observable, on
the other hand.

> and 2) the mechanism proposed for bolide-induced enanti
> extinction requires a lot of angels dancing on pins, viz., enantis and
> neos--both perfectly capable of dispersal (one would expect)

We've been through that discussion. Lots of bird species refuse to fly over
water.

> --have to be hermetically sealed in seperate
> hemispheres, i.e., neos only in the south.

It _helps_ when there are only neos in Antarctica and both everywhere else.
But the key factor may be ecological. Birds less dependent on green plant
matter won't die out as easily in an impact. Shorebirds that can eat
carrion, or chicken-like birds that can eat seeds, are expected to fare
better than arboreal ones that eat herbivorous insects (erm... especially
when all trees have burnt down).

> If neos did ascend via competition, myriad possibilities
> exist for how, including: behavioral advances, reproductive advances,
> flight characteristic advances, etc., etc.

Then go on and make a testable hypothesis out of that.

> > > marsupial extinctions were due to
> > > competition/predation from eutherian invaders;
> >
> > Metatheria and Eutheria coexisted from their divergence early in the K
to
> > the K-T throughout Asiamerica; after it Eutheria diversified, while
> > Metatheria hardly did -- but it held on far into the Miocene throughout
> > Laurasia. Metatheria lost much of its diversity at the K-T, so probably
did
> > Eutheria, but its fossil record is even worse.
>
> OK.  But replacement by invaders is documented in Van Valen paper of
> 60's.  (ref. if needed).

And nowhere since... looks like I don't need that 40-year-old paper. In
addition, I'm sure Van Valen only looked at NA, or only at the Hell Creek,
and didn't know about the current concepts of therian phylogeny. Where is
that Asian clade of Eutheria, where is Deltatheroida in the Cenozoic? Where
are the Asian members of Stagodontidae? Where are *Asiatherium* and
*Marsasia* (OK, the latter IIRC is Coniacian)? Are there any palaeoryctids
(like *Cimolestes*) or leptictids (like *Gypsonictops*) in K Asia? I don't
know of any. If there really weren't any, said groups can't have immigrated
from Asia to NA.

> All sorts of reasons why marsupials may have
> fared better in some places rather than others...

All discussed over and over onlist. I think your point is thoroughly
defeated.

> > > pterosaurs were barely
> > > hanging on (i.e., diversity was lowest ever _before_ K/T);
> >
> > Given the few presently known fossils, I'll believe that their diversity
in
> > the Maastrichtian was the lowest ever; but I'm not sure I'd call the 3
> > biggest flying animals ever "barely hanging on". I also don't know how
old
> > things like *Ornithostoma* are.
>
> But the disappearance of smaller forms is _very_ important.  Creatures
> don't just surrender niches.  The smaller forms were kicked out.  Birds
> must be prime suspect.  Again, bolide not a player.

Whatever happened, it happened long, long before the K-T boundary and so has
nothing to do with it. Other candidates: the Aptian-Albian and the
Cenomanian-Turonian mass extinctions. Looks like really small _adult_
pterosaurs have always been rare.

> Have we finished with the eggs in China, and the hadrosaur bone in SW
> NA?

Yes. The former simply occur below Paleocene mammals, and the K-T boundary
is not preserved. :-) The latter has been contended onlist repeatedly.

> By the way, if it's the paper I've been talking about (Bajpai
> and Prasad 2000) they're not saying therapod bones are Paleocene--since
> they were found with Late K ostracods--they are saying that the teeth,
> shells, are above the iridium layer.

Ah, so they say the boundary layer is below the boundary in that place!
Very, very strange, as it is _at_ the boundary _everywhere else in the
world_.

>  Anyway, we have found bones so close to the
> boundary, Signor Lipps says their existence in P. is a cinch.

Signor-Lipps says _nothing_ in that direction. What it says is only that
unless we sample really hard and the fossil record is good enough, we can't
tell a gradual from a catastrophic mass extinction, because both look
gradual.

> Absence of drastic teleost extinctions;

I know much too little about that. All I know is Ichthyodectidae is absent
from the Cenozoic. :-]

> spotty angiosperm extinctions (i.e., local effects);

I don't think we know that. I mean, in earlier times paleobotanists seem to
have done it that way... "that leaf looks like *Platanus*, that leaf looks
like the oddest living species of *Quercus*, that leaf looks like
*Viburnum*, that's *Acer*... yay, we had the whole modern flora in the
LK!!!" (At least it comes out that way in the popular literature, in
artistic reconstructions and in most texts I've seen so far.) Well, we don't
know if anything K that looks modern is modern. Pollen -- not found
associated with leaves -- seem to suggest otherwise. See
http://www.dinosauria.com/jdp/misc/hellcreek.html.
        Didn't Cheirolepidiaceae, the Mesozoic tropical conifers, die out
then?

However, plant survival is expected in the form of seeds that can remain
dormant for decades.

> low and declining diversity of ammonites

Wrong.

> and their turtle friends;

Sure?

> possible disappearance of smaller dinos;

Well, the only known really small certainly adult dino is *Microraptor*.

> slight relaxation
> in size constraints for pre-K/T mammals (in NA, at least);

*Repenomamus*! *Gobiconodon*! *Kollikodon*! All EK.

> failure of
> dinosaurs to re-establish dominance in post-K/T world

That's IMHO very good evidence that no viable populations survived the K-T.

> (i.e., other species
> make life for otherwise fab body plan miserable

Hardly testable.

> --this may provide an inference for pre-K/T dinos
> especially if bird and mammal hypos pan out)

I don't understand that.